Traffic calming: vehicle noise emissions alongside speed ...
50
TRL Report 180 Traffic calming: vehicle noise emissions alongside speed control cushions and road humps by Phil Abbott, John Tyler and Roger Layfield
Transcript of Traffic calming: vehicle noise emissions alongside speed ...
TRL Report 180
Traffic calming: vehicle noiseemissions alongside speed control
cushions and road humps
by Phil Abbott, John Tyler and Roger Layfield
The Transport Research Laboratory is the largest and most comprehensive centre for the study of roadtransport in the United Kingdom. For more than 60 years it has provided information that has helped
frame transport policy, set standards and save lives.
TRL provides research-based technical help which enables its Government Customers to set standards
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encourage good traffic engineering practice.
As a national research laboratory TRL has developed close working links with many other internationaltransport centres.
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TRANSPORT RESEARCH LABORATORYAn Executive Agency of the Department of Transport TW*L
~m Wmm—
.
TRL REPORT 180
TRAFFIC CALM~G: VEHICLE NOISE EMISSIONS ALONGSIDESPEED CONTROL CUSHIONS AND ROAD HUMPS
by Phil Abbott, John Tyler and Roger La~leld
Prepared for: Project Record: UG24 Speed Control HumpsRequiring Authorization
Customer: Driver Mormation and TrtiIcManagement Division, DOT (Mr E H E Wyatt)
Crown Copyright 1995. The contents ofthis report are the ~sponsibihty of tie authors and the ChiefExwutive of~.They do not nwessarily represent the views or poficies of the Dep-ent of Transport.
Transport Research LaboratoryCrowthorne, Berkshire,RG456AU1995
ISSN 0968-4107
CONTENTS
Executive Summary
Abstract
1. Introduction
2. Experimental design
2.1 Vehicle selection
2.1.1 Light vehicles
2.1.2 Buses
2.1.3 Comrnercid vehicles
2.2 Roadprofiles tested
Page
1
3
3
4
4
4
5
5
5
2.2.1
2.2.2
2.2.3
2.2.4
Speed control cushions(A,B,C,D,G,H and I) 5
Speed control humps @ and F) 6
Poorly maintained road (R and T) 6
Level road L)
2.3 Measurement method and anrdysis
2.3.1 Vehicle operation and speed
measurements
2.3.2 Vehicle noise measurements
2.3.3 Analysis
3. Results and discussion
3.1 Vehicle noise levels and road speed
3.1.1
3.1.2
3.1.3
3.1.4
Level road
Light vehicles (dl profiles)
Buses (dl profiles)
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7
7
7
8
8
8
8
10
12
Cornmercid vehicles (dl profiles) 12
3.2 Comparing vehicle noise levels atlocations alongside differentroad profiles 13
3.2.1
3.2.2
At a reference speed of 25~ 13
At a speed typical for the type
of road profile 16
3.3 Estimating changes in roadtraffic noise levels
3.3.1 Narrow cushions
3.3.2 Wide cushions
3.3.3 Speed control humps
4. Summary and conclusions
5. Acbowledgements
6. References
Appendix A: Photographs
A.1 Test vehicles
A.2 Surface profiles
Appendix B: Regression analysis of vehiclenoise and speed
Appendix C. Vehicle noise and speed for
buses and commercial vehicles
C.1 Buses
C.2 Commercial vehicles
Appendix D: Traffic noise prediction model
D.1
D.2
General
D.1.1 Basic equation for predictingtrtilc noise levels, LAW
Comparing measured and predictedchanges in traffic noise levels
D.2.1 Input parameters
D.2.2 Results
Page
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20
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25
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EXECUTIVE SUMMARY
Vehicle andtrtilc noise surveys alongside road humps and
speed control cushions have previously been carried out in
residential mess in Slough and York. These surveys showed
that following the introduction of the speed control meas-ures there was a reduction in the maximum noise emissionlevels from tight vehicles and in the overall tfilc noise
levels measured outside residential properties.
Mist these results were encoura@ng, the numbers ofcommercial vehicles and buses that could be included in
these surveys were insufficient to estabhsh the itiuence ofthe speed control measures on the noise emission levels forthese types of vehicles. It was, therefore, recommendedthat off-road trirds should be undertaken to examine therelationship between vehicle noise emission and vehicle
speed for a wide range of vehicles traveling over a range of
speed control cushions and road hump designs.
A study to investigate these factors was carried out on the
TM test track during the period November 1994 to Febru-
ary 1995. The work was funded by the Driver hforrnationand Trtilc Management Division, DOT.
The objective of the study was to compare the noise
emission levels for a range of vehicles travelhng over
different designs of speed control cushions and humps. Alevel road surface, typical of a road in good condition, anda road surface with a trench and ramp, simulating a poorlymaintained road, were dso included for comparison pur-
poses. The range of vehicles included a passenger car andrnik float; a midi, a single-decker and double-decker bus
and a totrd of 6 commercial vehicles with gross weightsranging from 16t to 38t. The selected commercial vehicleswere chosen to be representative of the current fleet in the
UK but prone to generate above average levels of body
noise (i.e. noise generated mainly from rattfing body pan-els, metd-to-metd impacts in the suspension etc.).
Initially comparisons were carried out with the vehicle
noise levels normrdised for a given road speed of 25 M
(16 mph). A further comparison was made, with vehiclenoise levels normtised to road speeds chosen to be typicalfor the particular design of speed cushion or hump, so thatchanges in vehicle noise levels following the installation ofthese measures could be estimated. The results obtainedwere then used as input to a prediction model to estimatechanges in traffic noise levels for different proportions ofcommercial vehicles in the trtilc stream.
Overall tr~lc noise level
As expected from previous work, it was found that where
the trtilc stream consisted mainly of fight vehicles, there
were substantial reductions in traffic noise levels. The
estimated reduction in trtilc noise was about 5 ~(A)
alongside the speed cushions and about 7 ~(A) alongsidethe road humps. However, as the percentage of commercialvehicles and buses increased, the mticipated acoustic ben-
efits gained from instdfing the various types of cushionsand humps dramatically deteriorated.
For example, when the traffic stream consisted of 10 percent commercial vehicles and 1 per cent buses, the esti-mated change in traffic noise levels was zero alongsidenarrow cushions (width less than 1700mm) and an increase
of 7 ~(A) alongside wide cushions (width greater than1700mm). The acoustic performance of the two road humpdesigns dso differed, with the ‘flat-top’ hump causing anincrease of about 6 &(A) and the ‘round-top’ hump asso-
ciated with a more gradud deterioration in performanceand still able to maintain a reduction of about 1 ~(A) in thelevels of traffic noise.
Interestingly, where the trtilc stream consists of more than
109o commercial vehicles the estimated change in noiselevel becomes less sensitive to changes in the proportion of
commercial vehicles in the traffic stream. For example, inthe case of the ‘flat-top’ hump the estimated change intrtilc noise level altered by about 13@(A) as the propor-tion of commercial vehicles increased from O to 1090compared with only a further 2~(A) change when theproportion of commercial vehicles increased from 10 to20%.
1
VeMcle noise emissions
For the car and buses, there was httle difference in averagevehicle noise levels at a reference speed of 25 W be-
tween the narrow and wide speed cushions categories and
the ‘round-top’ and ‘flat-top’ humps. However, vehiclenoise emission levels over the road profiles which simu-
lated a poorly maintained road (i.e. the ramp and trench)
were on average between 4 to 6 W(A) higher than com-pared with noise levels measured on the level road surface,
and alongside the road humps and speed control cushions.
In the case of corrunercid vehicles, average noise levelswere about 8 ~(A) higher alongside the wide cushions andthe ‘flat-top’ road hump than alongside the narrow cush-ions and the ‘round-top’ hump. It was dso found that the
differences in noise levels between the two hump designswere speed dependent, with higher speeds resulting insmaller differences in vehicle noise. Furthermore, vehiclenoise levels were, on average, about 11 ~(A) higheralongside the ramp and trench compared with noise levels
generated at the same speed on the level road, and alongsidethe narrow cushions and ‘round-top’ hump.
Comparing vehicle noise levels within each of the two
speed cushion groups showed little variation in noise levels
at a given reference speed for each vehicle catego~. Small
differences in noise levels of about J.5 ~(A) were foundbetween cushions constructed of different materials (as-
phalt and moulded rubber) and similarly differences ofabout 2 ~(A) were found between single cushions anddual cushions, spaced in single file and 4 metres apart. Atthese low speeds (25~) differences were not statisti-
cally significant and their rank ordering depended on thevehicle category being considered.
Estimates of the change in vehicle noise levels before and
after instdhng speed control cushions indicate that for boththe car and bus categories, the noise levels alongside thewide cushions were, respectively, about 2 and 1.5 ~(A)lower than compared with the narrower cushions. Simi-larly, noise levels alongside both types of humps were
about 4~(A) lower than compared with the narrower
cushions. However, the noise levels for the commercirdvehicles were, on average, about 6 &(A) higher alongside
the wide cushions and about ~(A) higher alongside the‘flat-top’ hump than at the narrower cushion. In addition,for dl the vehicle categories, noise levels alongside the
‘round-top’ hump were about 4 ~(A) lower when com-pared with the narrow speed cushions.
The conclusions from this work are timited by the type of
vehicles included in this study, particularly with the selec-tion of commercial vehicles which were chosen to demon-
strate possible ‘worst case’ effects since these vehicles
were known to be prone to the generation of body noisewhen driven over uneven surfaces. Furthermore, the results
of the estimated change in noise levels following the
installation of the various speed controlling measures refies
on accurately estimating the change in vehicle road speeds.
This is particularly important in the case of the ‘round-top’
hump where the slope in the relationship between noise and
speed for commereid vehicles is large. A small error in
estimating the reduction in road speed for commercialvehicles, following the installation of ‘round-top’ humps,may lead to significantly different results from that re-
ported here.
All the commercial vehicles were tested unladen and dlhad metal suspension systems. A further off-road trial isbeing conducted at TN and will investigate the influenceof load on noise emissions from commercial vehicles andwill include a selection of vehicles with air suspension
systems which are known to have significantly lowersuspension related noise when compared with conven-
tional steel sprung suspension systems.
It will be possible to use the spee~evel functions deter-
mined for the narrowest cushion in these off-road trials (i.e.
width 1500 mm) to predict changes in noise levels once
suitable ‘before’ and ‘after’ speeds are available from testsites on the pubhc roads. The speed and noise measure-ments currently being carried out at the trunk road traffic
cahning scheme on the A49 in Shropshire should give anindication of speeds at these cushions and an opportunity tocheck predicted changes in noise levels with measuredvalues.
In summary, the results of this work indicate that, if thereare any commercial vehicles in the traffic stream, trafficnoise levels may increase after the installation of widecushions or ‘flat-top’ humps but they will be less affectedby the installation of narrower cushions or ‘round-top’
humps, particularly where the proportion of commercialvehicles exceed 570 of the totrd trtilc flow.
2
TRAFFIC CALMING: VEHICLEALONGSIDE SPEED CONTROLROAD HUMPS
ABSTRACT
Various trfilc calming schemes have been introduced bylocal authorities to slow trtilc but the most effective
usually involve some form of vertical deflection, normallyin the form of a road hump or speed cushion. Although,
vertical deflections are effective at reducing trfic speed
there has been concern raised by some local authoritiesabout disturbance to residents from vehicle noise and
ground vibrations as well as discomfort to road users.
The objective of this study was to compare the noiseemission levels for a wide range of vehicles traveling over
different designs of speed control cushions and humps; thevehicles included: a car, different types of buses and a range
of commercial vehicles (gross weights 16t to 38t) whichwere chosen to demonstrate possible ‘worst case’ effectssince these vehicles were known to be prone to generateabove average levels of suspension related noise and bodyrattles etc. when driven over uneven road surfaces.
The results have been used to predict the change in trfilcnoise levels following the instrdlation of such speed control
measures for different proportions of buses and commer-
cial goods vehicles in the trtilc stream. Predicted changesin trtic noise levels were shown to be in good agreementwith site measurements.
1. INTRODUCTION
Trfilc cting schemes have been introduced by manylocal authorities in Great Britain with the aim of reducingspeeds md injury accidents. Various measures have beenused to slow trtilc but the most effective usually involve
some form of vertical deflection, normally in the form of aroad hump or speed cushion. Speed cushions are aimed atreducing the higher levels of passenger discomfort found in
large vehicles at road humps, and differ in design from roadhumps in that they do not extend over the whole width of theroad. They are raised areas in the carriageway which are
designed so that cars which have comparatively narrow
tracks cannot avoid them and have to slowdown to preventdiscomfort. Larger vehicles with wider tracks, such as
buses, fire appliances and ambulances, can straddle theraised area and cross the cushions relatively unimpeded.
While vertical deflections are effective at reducing trtilcspeed Webster, 1993), there has been concern raised bysome local authorities about disturbance to residents from
NOISE EMISSIONSCUSHIONS AND
vehicle noise and ground vibrations as well as discomfort
to road users. Driver Information and Traffic ManagementDivision, DOT has funded research at ~into vehicle and
traffic noise levels, and ground vibration levels at roadhumps and speed cushions.
The introduction of a speed reduction measure such as a
road hump or speed control cushion
can itiuence trtilc noise levels in a number of ways. Forexample, lowering the speed of vehicles may mean thatvehicle noise emission levels are lowered. In addition, after
the measures are installed trtilc flows may be reduced,
leading to further reductions in noise levels. However,vehicle noise emissions may dso depend upon the way the
vehicle is driven; with a passive style of driving, at a lower
but constant speed, contributing to lower noise levels; andan aggressive style, with excessive braking and accelera-tion between speed control devices, giving rise to a highlyfluctuating noise level which can contribute to noise distur-bance to residents. In addition, the use of road humps andspeed cushions to reduce trtilc speed may give rise to
vehicle body noise (e.g. body rattles, suspension noise etc)which may be a cause of noise disturbance.
Vehicle and traffic noise surveys have been carried out
alongside speed control humps in Slough and speed controlcushions in the City of York in 1993 and 1994 (Abbott,
Philfips and Layfield, 1995). These surveys showed that
following the introduction of such speed control measures
there was a reduction in the maximum noise emissionlevels from tight vehicles @assenger cars ad small vans
with unladen weight less than 1.5 tonnes) at sites alongside,and between, the speed control humps or cushions. Thereduction in fight vehicle noise levels was found to be
consistent with that expected due to the drop in vehiclespeeds. Overall trtilc noise levels at these sites were dsoreduced and the lower trtic noise levels could be ac-
counted for by the subsequent reduction in the volume oftraffic, composition and speed.
However, whilst these results are encouraging the numberof commercial vehicles (unladen weight greater than 1.5
tonnes) and buses in the survey were insufficient to estab-tish the influence of the speed control measures on the noise
emission levels for these types of vehicles. It was therefore
recommended that off-road trials should be undertaken to
examine the relationship between vehicle noise emissionand vehicle speed for both types of vehicles traveling overa range of different cushion and hump designs.
3
A study to investigate these factors was carried out on the
TRL test track during the period November 1994 to Febru-
ary 1995. A range of vehicles was tested including a car, 3
different types of buses, and 6 commercial vehicles se-lected from types known to be susceptible to the production
of body noise. The humps and cushions tested included
designs usedin urban traffic cahrdng schemes and a narrow(1500mrn wide) cushion which is being tried out as part ofa package of trfic calming measures for use on trunkroads through villages.
In addition to examining the ifiuence of different designs
of speed control cushion and road humps on vehicle noise
emissions, the results have been used to estimate the changein trtilc noise levels following the installation of such
speed control measures for different proportions of buses
and commercial goods vehicles in the traffic stream.
This report describes the experimental methods used in the
investigation of noise levels and gives a summary of theresults obtained and the conclusions reached. Further re-
search at TRL into the levels of ground vibrations at road
humps and speed cushions is planned for autumn 1995.
2. EXPER~ENTAL DESIGN
The aim of the study was to measure the noise from eachvehicle as it travelled over different designs of speed
control cushionfiumps for a range of vehicle speeds. The
cushionshumps were constructed in the Central Area of the
TRL test track. In addition measurements were carried out
with each vehicle traveling over a level road surface, to
provide basetine noise levels, and two further surfaceswhich contained surface irregularities designed to be rep-
resentative of typical road surface features that might beencountered on pubhc roads in poor condition.
2.1 VEHICLE SELECTION
Table 1 hsts the different types of vehicles used for this
study. Vehicles were classified into three categories: tightvehicles (unladen weight less than 1.5 tonnes); buses; and
commercial vehicles (unladen weight greater than 1.5
tonnes). The width between the wheel tracks is dso givenin Table 1. Each vehicle was given a code name for easy
identification and a photographic record of each vehicle
together with the code name is included in Appendix A. 1.
2.1.1 Li@t veticles
The tight vehicle catego~ consisted of a typical passengercar - a Ford Escort 1.6 titre petrol engine saloon ~ 1) anda Smith electric mik float (V2). The rnik float was in-
cluded to represent a vehicle hkely to generate impactnoises from the empty rnik crates when crossing thecushions.
TABLE 1
Vehicles used in the study
Vehicle Wheel track
category and Description width
code name (inside tyres) mm
Front Rear
Light
V1 Passenger car (1.61 petrol) 1270 1260
V2 Mik float 1200 1200
Buses*V3 Midi-single decker 1690 1200
V4 Single-decker 1830 1270
V5 Double-decker 1830 1270
Commercial vehicles*V6 2-axle rigid curtain-sided, 16t gvw 1790 1210
V7 2-axle rigid drop-sided, 16t gvw 1840 1240
V8 2-axle rigid box body, 16t gvw 1750 1240
V9 2-axle skip lorry / empty skip, 16t gvw 1800 1250
Vlo 3-axle rigid tipper, 24t gvw 1820 1340
Vll 2-axle artic skeletal trailer with Tractor 1770 1180
empty containers, 38t gvw Trailer 1240
. . . . .* All buses had air suspension whilst the comrnercla vetucles had metal suspension
4
2.1.2 Bus=
The bus category included a Mercedes 21-seater midi-bus
(V3), a DAF single-decker bus (V4) and a DAF double-decker bus (V5). All three types of vehicles had air suspen-sion systems.
2.13 Commercial vehicles
A total of 6 commercial vehicles were selected with grossvehicle weights ranging from 16t to 38t. The selection was
based on the findings from a separate survey, carried out at
TRL, to examine the generation of body noise from a
sample of commercial vehicles. The selected vehicles were
not modified in anyway and were chosen to be representa-tive of the current fleet in the ~ but which wem suscep-tible to the generation of high levels of body noisel. All sixtypes of vehicles had metal suspension systems.
2.2 ROAD PROF~ES TESTED
The different types of road profile tested in this study (i.e.
speed control cushions, road humps, a trench and ramp tosimulate a poorly maintained road surface and a level
surface typical of normrd road conditions) have been di-vided into 5 profile groups with a separate code letier to
identify each individud design. Table 2 gives a brief
description of each profile group together with the indi-
vidud code letter for each design. A photographic record of
each road profile is given in Appendix A.2. together with its
code letter for identification.
2.2.1 Speed control cushions (A,B,C,D,G,Hand I)
The general design features of the speed control cushionsexamined in this study are shown in Figure 1. The overall
‘ Body noise refers mtinly to the noise generated by metal-to-meti impacts in tie susknsion, container, body panels and loosely fittingcomponents such as handles etc, ad by vibration of body panels.
TABLE 2
Description of each road profile including the specification of speed control cushions
and humps constructed on TRL test track
Dimensions
Profile group and code Construction Overall Overall Height Otioff Side wdlwidth length gradient gradient(mm) (mm) (mm)
Narrow cushions(width e 1700mm)
B Asphalt 1600 2000 75 1:8 1:4c Asphalt 1600 3500 65 1:8 1:4D Asphalt 1500 3500 60 1:8 1:4
Wide cushions
(width > 1700mm)A Asphalt 1900 2000 75 1:8 1:4
G Moulded rubber 1900 1950 75 1:8 1:4H Moulded rubber 1880 2380 80 1:5 1:5I Asphalt Same as A but two cushions in single file 4m apart
HumpsE (’flat-top’) Asphalt 4000 7800 75 1:12 1:4
F (’round-top’) Asphalt 4000 3700 75 ‘round-top’ profile
Poorly maintained road
R (ramp) Plywood 3000 600 Ramp: vertical drop 25rnmT (trench) Concrete 3000 1200 Trench: max. depth 40mrn
LevelL Asphalt Hot Rolled Asphalt (HRA) and
Fine Textured Asphalt ~A)
5
Directionoft ravel
+ off
Side wall
Podiumwidth I(Pw)
1
Side wall
On Overallwidth(Ow)
/ \ —
D
Overall lengthI
(OL)
Fig. 1 General design of speed control cushions
specifications for each type of cushion is shown in Table 2.The cushions have been divided into two profile groups:
narrow cushions where the overall width is less than
1700mm and wide cushions where the overall width is
greater than 1700mm.
(a) Narrow cmhions @,C and D): The narrow cushionsvaried in width from 1500rnm (D) to 1600mm (B C) and in
height from 60mm @) to 75rnm @). All the narrow
cushions were constructed from asphalt and had odoffgradients of 1:8.
(b) Wide cushions (AJ,G and H): The wide cushionsvaried in width from 1880mm ~) to 1900mm (A, I & G)
and in height from 75rnm (A, I&G) to 80mrn ~). CushionI consisted of two cushions laid in single file 4m part, eachwith a similar specification as cushion A, both constructed
from asphalt. Cushions G and H were proprietary designs
constructed from moulded rubber. Cushions A, I & G hadodoff gradients of 1:8; cushion H had a rounded odoff
ramp profile with an average gradient of 1:5.25.
2.2.2 Speed control hmps (E and F)
Two types of speed control humps were included in this
profile group, both 4000mm wide and 75mrn high. E had a‘flat-top’ profile and with a plateau length of 6 metres
(overall length 7.8 metres) and an otioff gradient of 1:12.
F had a ‘round-top’ profile with an overrdl length of 3.7
metres, as shown in Figure 2(a).
2.2.3 Poorly maintained road (R and T)
A further profile group was included to represent typicalprofiles of poorly maintained roads. The ramp (R) and
trench (T) were designed from survey measurements ofsurface irregularities where the road had been poorly rein-
stated after road works had been carried out watts 1988,1989), see Fig 2@) and Fig 2(c).
2.2.4 Level road (L)
The find profile group was included to represent a typicallevel road. The hot rolled asphalt @RA) surface waslocated on the Long Straight section of the TRL track and
designed specificrdly for high speed motorway conditions
with maximum stone size aggregate of 20mrn. The materirdspecification is given in BS 594 @ritish Standards Insti-
tute, 1985). A further surface was selected in the Central
Area where the humps and cushions were laid. This surfacewas a fine textured asphalt VA) surface. The texturelevels for atypical residential road surface would norrndly
fdl within the range of textures of the two types of surfacesincluded in this study.
6
(a) ‘Round-top’ hump (~
2.3
2.3.1
t
3700mm
i
(b) Ramp (R)
1-600mm
Ii
Direction of traveli +
25mmI
I\450
(c) Trench (C)
I 1200mm I
I 40mm
Fig. 2 Profiles of ‘round top’ hump, ramp and trench
~AS~~NT ~THODAND ANALYSIS
VeMcle operation and speedmeasurements
Prior to each test session the tyre pressures for each vehicle
studied were checked and the vehicle driven for about 10minutes to ensure that the engine components and the tyreswere at norrnd operating temperature.
For each road profile each vehicle being studied was driven
through the test site under power and at a steady speed. Thetarget speeds encompassed the range 15-40 ~ and were
chosen to cover a reasonable range of operating conditionsin practice. Prior to the main testing, appropriate gearselections were made for each vehicle and for each targetdrive-by speed. The gear selected was chosen so that the
engine was not operating at either an unduly high enginespeed for the gear selected nor was the vehicles enginelabouring to achieve the required speed. The gear eventu-
rdly selected for each target speed for a particular vehiclewas not rdtered throughout the total test period covering the
range of profiles studied.
Speeds were monitored at the trackside using a portableradar gun giving a digital read out of speed. A diagramshowing the layout of the test site is shown in Figure 3. The
direct readings of speed were relayed to the driver of the
vehicle using track radios which acted as an aid to the driver
to adjust the speed setting during the approach to the testsite. In this way the correct target speed was achieved as thevehicle passed through the site. The drivers were instructed
to keep the centre of the vehicle positioned along the centrehne of each test site throughout the pass-by event. Thus, thevehicle would pass over the speed cushions with either
wheels on both sides on (or o~ the cushions (depending on
track width) and not with wheels on one side on and on the
other side off.
2.3J Veficle noise measurement
Noise measurements were taken with a microphone located
7.5m from the centre of each test site and at a height of 1.2m
above the track. This microphone location was selected asit is generally accepted as a reference position for measur-ing vehicle noise emissions (1S0, 19@). An additionalmicrophone was located 4.5m from the centre of the speedcontrol cushion sites when the passenger car was tested.This was to enable the results to be compared with resultsfrom the York surveys where a sifilarly located micro-
phone position was used. The microphone was fitted witha standard foam windshield to reduce the influence of windturbulence around the microphone affecting the measurednoise levels, although dl tests were only conducted during
cdm weather conditions when the test surface was dry. Ford] the measurements each vehicle approached the test areawith the microphone on the nearside.
7
Speed cushion Test vehicle
---- ---- ---- ---- ---- ---- -- -\---------------
Fig. 3 Vehicle noise measurement layout
During each drive-by test the signal from the microphonewas relayed to a precision sound level meter configured to
capture the maximum A-weighted noise level dB(A) witha response time set to F weighting (British StandardsInstitution, 1994). This noise level together with the vehicle
speed was recorded.
The microphone and sound level meter system was crdi-
brated before and after each measurement session using aprecision lMz tone c~brator.
2.33 Analysis
Using standard computer software the maximum noiselevel recorded during each drive-by together with thelogarithm of speed were plotted and a linear regression
analysis using the method of least squties was carried outfor each individurd road profile.
Figure 4 illustrates the method of analysis used. The Figure
shows a typical plot of the maximum noise level with thelogarithm of vehicle speed together with the regression fine
for the passenger car traveling over hump F.
The relationship between vehicle noise level and thelogarithm of vehicle speed operating under steady
speed conditions is often referred to as the speedllevel function.
3. WSULTS AND DISCUSSION
The results of the regression analysis carried out on eachvehicle and for each road profile are given in Appendix B.The regression analysis statistics have been tabulated sepa-
rately for each vehicle and are given in Tables B. 1 to B. 11.
The results showing the variation in vehicle noise level
with speed are presented in Section 3.1 commencing with
the results obtained for the level road profile in Section3.1.1. This is followed by the results for the remaining
profile designs separated into different vehicle categoriesin Sections 3.1.2 to 3.1.4.
A comparison of vehicle noise emissions for the vtious
profile designs is initially examined in Section 3.2.1 for areference speed of 25M. A further comparison is car-ried out in Section 3.2.2 using vehicle speed information
gathered from existing traffic calming schemes wherecushion and humps have been installed.
Finally in Section 3.3, a prediction method is describedwhich uses as input the spee~evel finctions @ven inAppendix B to provide a broad indication of the Wely
change in trtilc noise levels following the introduction of
speed control measures for a range of traffic scenarios.
3.1 VEHICLE NOISE LEVELS ANDROAD SPEED
3.1.1 hvel road
Before comparing the vehicle noise levels for different roadprofiles it is interesting to understand the relationship
between vehicle noise and speed for the different categories
of vehicles traveling on a level road.
Figure 5 shows, for each vehicle catego~, the regressionfine indicating the measured variation in noise level withspeed. For both the bus and commercial vehicle categoriesthe data for each vehicle within the respective categories
have been combined to obtain the overall regression. Datafor the mik float has been excluded from this analysis due
to it being an atypical vehicle. The noise levels for both the
8
A Datapoint
Regressionline
\
A
Correlation coefficient (r) = 0.986
I I I10 20 30 40 50
Vehicle speed (km)
Fig. 4 Example illustrating regression analysis of noise leveland speed for the car traveling over hump F
Commercial vehicles
\~
--.0-0 ---0
----*---
---0
-----0-”
----
/Buses
Cars
L
10 20 30 40 50
Vehicle speed (km)
Fig. 5 Variation in noise level with speed for different vehicle categoriestraveling on a level road (HRA)
9
commercial vehicles and buses were higher than for the car,
as would be expected, but the noise levels for the car were
more dependent on speed than for the other vehicle catego-
ries. For the car category, as vehicle speeds increase the
noise generated by the impact of the tyres with the roadsurface begins to dominate the overall vehicle noise level,whereas for buses and co-ercid vehicles, the dominantnoise source is from the engine and exhaust system which
is less influenced by changes in vehicle speed.
The data in Figure 5 shows that provided the introduction
of speed control measures does not significantly alter thespeetievel function for the various categories of vehicles
then, the reduction in overall trtilc noise will be highly
dependent on the number of commercial vehiclesbuses inthe @lc stream both before and after such measures areintroduced. For example, the estimated reduction in overall
trfic noise level from reducing vehicle speed from 40 to
20M would be about 10 dB(A) for a traffic stream
consisting of dl cars whereas a reduction of only about 2dB(A) maybe expected ifthetrtilc stream is dotinatedby
commercial vehicles. In addition, the use of physical trafficcahning measures such as humps and cushions whichvertically deflect the vehicle may cause additiond body
noise to be generated which may therefore offset anyacoustic benefit gained from a reduction in speed. The
purpose of the trials on the TMtest track was to investigatethe overall effect of the humps and cushions on vehiclenoise, particularly for buses and heavy goods vehicles
80
which are known to be susceptible to significant levels of
body noise from previous surveys carried out at T~.
3.12 Li@t veticles (d profdes)
The results from the regression analysis of noise level andspeed for the tight vehicles travelhng over the humps,cushions, and irregular surfaces are given in Appendix B.
Tables B. 1 and B.2 are for the car and rnik float, respec-tively.
(a) Passenger mr: The regression tines showing the vari-ation in noise level with speed, measured at a reference
distance of 7.5m, for the passenger car travelhng over the
various profile designs, are shown in Figure 6.
The results show that for the five different types of profiles
the slopes of the regression fines were on average similarindicating that the change in noise level with speed was
essentially independent of the road profile.
Noise levels for the car travelhng over the ramp weresi~ficantly higher than for the other profiles by approxi-
mately 9dB(A) and illustrates the importance of properly
reinstating the road so that the surface profile is level.Although both the spee~evel functions for the wide cush-ions and the trench are similar and marginally give higher
noise levels than both the narrow cushions and the humpsfor a given road speed, these differences are small, between
Narrow cushions: width c 1700mmWide cushions: width > 1700mm
Ramp (R)
f
\
Narrow cushions
Wide cushions(AIGH)
Humps (EF)
5010 20 30 40 50
Vehicle speed (km)
Fig. 6 Noise level from a car traveling over different profiles
10
■ Gale Lane data■
n■
*■
■
■
Regression line for light vehicles ● L“alongside cushions (width: 1700mm) n A-in Gale Lane, York
●
1
.*■ b
:0*.*
-“~#-
■ ##-*- Regression line for passenger car
alongside narrow cushions(width: < 1700mm) at TRL test track
T-Regression line for passenger caralongside wide cushions(width: > 1700mm) at TRL test track
■■
■■
■
10 20 30 40 50
Vehicle speed (kti)
Fig. 7 Comparing vehicle noise levels measured alongside a speed cushion in Gale Lane,York and TRL test track
1 to 2 dB(A), and of the same order as the average standarddeviation of the regression hnes, see Table B. 1 for theregression statistics.
In addition to noise measurements at areferencedistance of7.5m from the centre of the vehicle pass-by, measurementsat 4.5m were dso undertaken to simulate the measurementlayout used in the survey carried out in Gde Lane, York so
that the results from the off-road trial could be comparedwith actual survey data.
Figure 7 shows the noise levels and speed values forindividud fight vehicles measured alongside speed control
cushions in Gde Lane, York (Abbott et d 1995) togetherwith the regression hne drawn through the data points.
Included in the Figure are the corresponding regressionhnes derived for the passenger car from the off-road trials
carried out at TN for both the narrow and wide speedcontrol cushions.
Comparing the regression tines shows that the noise leveland speed functions derived for the single passenger carfrom the off-road trials are in good agreement with actualsurvey data using different tight vehicles drawn from thetrtic stream. The shghtly higher noise levels in the Yorkstudy compared with the off-road trial is expected; the Yorksurvey was carried out in a residential area where reflectioneffects from houses may have contributed to the overall
noise level, whereas, in the off-road tids there were no
such reflecting surfaces present.
(b) Mflk float: The regression analysis statistics shown inAppendix B, Table B.2, for the mik float indicate that therewas generally poorer correlation between vehicle speedand noise for this type of vehicle traveling over the various
profile designs compared with the other vehicle types. Thisis perhaps not surprising due to the hmited speed range ofthe vehicle (maximum speed 23 M). However, d-althoughthe correlation coefficients were in general not high
there were some notable exceptions: hump F, cushion G
and the level road profile L, where the correlation coeffi-cients were 0.94, 0.87 and 0.71 respectively.
As the correlation between speed and noise is not signifi-
cant for this vehicle type it is perhaps only possible tocompare the influence of the various profile designs onnoise levels by examining average values. Included inTable B.2 are the average speed and noise levels measured
during each session for each profile design. Interestinglythe average noise levels for both the hump designs, E andF, together with cushion D gave the lowest values rangingfrom 64.9 to 67.4dB(A), comparable to the noise value forthe level road profile, L, of 67dB(A) at a speed of 19 ~.
Noise levels for the rnik float were higher than comparedwith the passenger car for similar average speeds. Included
11
in Table B.2 are the corresponding differences in noise there were significant differences in noise levels betweenlevels between the two vehicles averaged for each profile the two types of hump designs E andF, particularly with the
group. The mik float gave higher noise levels than the car double-decker bus, where the speed level function for the
by 6.6dB(A) for the level road surface to 19.7dB(A) for the ‘flat-top’ humpE was about 5dB(A) higherthanfor ‘round-
trench profile. The corresponding values for the other top’ profile hump F. However, for the single-decker bus,
profiles were in the rmge 10.7 to 14.OdB(A). hump F gave noise levels higher than hump E of between
3 to 5dB(A). For the rnidi-bus the different hump designs3.1.3 Buses (dl profiles) gave similar noise levels.
The results from the regression anrdysis of noise level and
speed for buses are given in Appendix B: Tables B.3, B.4
and B.5 for the rnidi, single-decker and double-decker
buses, respectively. The regression tines illustrating the
general relationship between vehicle noise level and thelogarithm of speed for each vehicle are shown in Appendix
Cl, Figures C.1-C.3
Figure 8 shows the average variation in noise level with
speed for dl the buses studied. Generally the results for thebuses indicate that on average the relationship betweennoise level and speed were sitila for both the narrow andwide cushions together with both the hump designs, a trendwhich was dso noted for the passenger car. The overallaverage noise level for the buses were higherthm the car by5 to 15dB(A) with the difference in noise levels increasing
as speed reduced.
Examining the individud spee~evcl functions for eachvehicle shown in Figures C. 1-C.3, however, shows that
Both the trench and the rmp, w~ch simulated a PoorlY
maintained road surface, generated higher noise levels for
the buses than the humps and cushions by between 5 to
15dB(A). The largest differences were noted at the higher
speeds. Again, this illustrates the importance of properlyreinstating the road so that the surface profile is level.
3.1.4 Commercial veficles (dl profiles)
The results from the regression analysis of noise level andspeed for the comercid vehicles are given in Appendix B:Tables B.6 to B.11. The regression fines illustrating thegeneral relationship between vehicle noise level and thelogarithm of speed for each vehicle are shown in AppendixC.2, Figures C.4 to C.9.
Figure 9 compares the average spee~evel functions for
each profile group across dl the vehicles studied. For thisrange of conunercid vehicles and over the speed range
studied, i.e. 15 to 40W, the noise level from vehicles
Narrow cushions: width c 1700mmWde cushions: width > 1700mm Ramp (R)
Narrow cushions
r
. . . .
Wde cushions Humps (EF) Level HA sutiace(AIGH) (estimated)
(T
20
Vehicle speed (kM)
30 40 50
Fig. 8 Average noise levels from all buses traveling over different profiles
12
Narrow cushions: w’dth c 1700mmWde cushions: width> 1700mm #e
#4
4
Trench (T)
Ramp (R)
Humps (E)
## ●.
. .●. -,
.**.-
--
/
..-. . --~--..” ---
..* *-”
Wde cushions-.
(AIGH).“OO ---
●.” - -
*-.-. -- .**
\
. .~.“ Level HA sutiace
Narrow cushions(estimated)
(BCD)
10 20 30 40
Vehicle speed (ktih)
Fig. 9 Comparing average noise levels for commercial vehicles alongside different road profiles
traveling over the narrow speed cushions (width less than1700mm) were generally significantly lower than com-
pared with the other profile designs apart from the ‘round-top’ profile hump Fat low speeds (i.e. less than 20 ~),where the average noise levels were similar. For example,
comparing the noise levels for the narrow and wide cush-
ions show differences of about 9dB(A).
Examining in more detail the speeflevel functions for theindividud vehicles shown in Figures C.4 to C.9 of Appen-
dix C, these illustrate the wide variation in the regression ofnoise level and speed for this vehicle category and range ofprofile designs examined. It should dso be noted that thetype of vehicles were dehberately chosen to be representa-tive of the type which are susceptible to high levels of bodyrattle noise in service. Care is therefore needed in using this
data to estimate changes in vehicle noise emissions due tothe installation of a particular speed control device forvehicles classified within this diverse category.
3.2 COMPAR~G WHICLE NOISELE~LS AT LOCATIONSALONGS~E D~FERENTROAD PROF~ES
Having established the relationship between vehicle noiselevel and speed for each vehicle and profile category the
maximum noise emission levels for a given vehicle/surface
profile can be estimated for a given speed. With thisinformation vehicle noise levels at sites alongside different
profiles can be compared.
The initial comparison, described in section 3.2.1 belowhas been carried out assuming a reference speed of 25M
h which equates approximately to the average speed ofvehicles after speed cushions were installed in the earfierYork trials (Abbott, Philhps and Layfield 1995).
A further comparison, given in section 3.2.2, was carriedout using average vehicle speeds collected at each of thesites where the different types of profile designs had beeninstalled.
3.2.1 At a reference speed of 2-
Table 3 shows the maximum noise level at a reference of25M derived from the spee~evel functions given inAppendix B for each vehicle category and each roadprofile.
(a) Car: Compting the noise level forthecartravelling onthe level ~ surface with noise levels for the narrow
cushions shows, surprisingly, that on average noise levels
on the level road were about 2.3dB(A) higher than alon-gsidethe nmow cushions and were significantly different
13
TABLE 3
Comparison of vehicle noise levels at a reference speed of 25ti
Profile Maximum noise level dB(A) at 7.5m and 25ti
grouplcode car Buses Commercial vehicles
bvel road
L2 64.4 75.3 78.6
~A3 62.7 71.4 78.4 (72.7)4
Narrow cushionsB 62.3 74.5 79.9
c 62.1 74.1 80.1
D 62.0 71.5 78.4 (73.5)5
Average 62.1 73.4 79.5
Wide cushionsA 63.1 74.6 88.2
I 64.5 72.7 89.3
G 64.7 73.7 86.8
H 63.8 72.5 87.4
Average 64.0 73.4 87.9
Humps
E (’flat-top’) 62.1 72.0 90.6
F (’round-top’) 62.4 71.8 82.7
Average 62.2 71.9 86.7
Poorly maintained roadR 71.3 79.9 90.7
T 64.3 76.5 92.6
Average 67.8 78.2 91.7
2 In addition to the hot rolled asphalt (~A) surface, measurements were carried out on fine textured asphalt ~A) sirnilm to the surfaceof the track where the speed cushions and humps were cons~cted.
3 Values in bold type are estimated noise levels, see text.
4 The value in brackets is the average of the maximum noise levels for two vehicles, V6 and V7, derived from the s~Mevel functionmeasured on fine textured asphalt (~A) similar to the surface of the track where the speed cushions and humps were constructed.
5 The value in brackets is the average of the maximum noise levels for two of the vehicles, V6 and V7, @aveUingover cushion D.
when compared with the standard deviation of the noiselevels with speed, shown in Table B. 1.
The higher noise levels recorded for the level HRA profilewere hkely to be due to the noise generated by the interac-
tion of the tyres with the road surface dominating overallnoise levels. The HRA surface is typical for high speed
trtic conditions with higher texture levels than comparedwith the type of surface where the cushionsfiumps were
constructed.
Aftierset of vehicle noise and speed level measurementswere carried out on the test track with the same vehicle but
where the surface was fine textured asphalt VA) and
similar to the track surface where the humps and cushionswere constructed. The regression analysis for this data set
is dso given in Table B. 1 and the results at the referencespeed included in Table 3. It can be seen that the noise levelat the reference speed for this surface was 62.7dB(A) whichwas, on average, only 0.6dB(A) higher than the corre-sponding results obtained with the narrow cushions.
Figure 10 summarises graphically noise levels given inTable 3. A value of 62.7dB(A) for the car category travel-
ing on the level road has been taken for comparison
purposes.
14
I Cars ■ Buses H Commercial ❑vehicles I
Levelroad
—Profile rode: L
Profile group:
Average for eachprofile group
n
1 23 4
Narrow cushions(width < 1700mm)
B
1
Mde cushions(width > 1700mm)
Humps
AIGH
2
EF
3
Poodymaintained
R T
4
Fig. 10 Comparison of vehicle noise levels for different road profiles at a reference speed of 25kfi
The results show that for the narrow cushions and the
humps the noise levels forthecar were similar at a referencespeed of25Wgivingvdues of62.ldB(A) and62.2dB(A),
respectively, and therefore, comparable with the value of62.7dB(A) obtained for the level surface profile.
For the wide cushions, noise levels for the car on averagewere marginally higher than the level profile by 1.30(A)
but compared with the standard deviation of 1.7dB(A) fromthe regression analysis for the profile group, (see TableB. 1), this difference was not statistically significant.
Comparing the designs which gave the lowest md highestnoise levels for the car within the group, cushions A
(63.ldB(A)) andG (64.7dB(A)), it is perhaps interesting to
note that although both cushions had identical dimensions
cushion A was constructed from asphalt, whereas, cushionG was constructed from moulded rubber. Differences innoise levels of 1.6dB(A) was not statisticrdly significant at
these low speeds, and for buses and commercial vehiclesthe noise levels at the rubber cushion G were shghtly less(about l~(A)) than at the asphalt cushion A. The’ noiselevels at the other rubber cushion H were similar (within
ldB(A)) to those of cushion G
The noise level for the carat cushion group I (two cushions
in single file 4m apart) was sfightly higher (1 .4dB(A)) thanat cushion A (single cushion with similar dimensions andmaterirds). A similar difference (0.9dB(A)) was observedfor commercial vehicles but for buses, the noise level atcushion group I was stightly lower (1 .9~(A)) than atcushion A.
Comparing noise levels from theprofilegroup representinga poorly maintained road @refile group 4) show that theramp profile produced significantly higher car noise levels
of 7 1.3dB(A) compared with 64.3 dB(A) for the trench and
62.7 dB(A) for the level surface profile.
In summary, therefore, noise levels for the car travelhng
over the vtious surface profiles at a reference speed of25~ were generally comparable with that obtained on alevel road surface of similar type, the exception was for theramp profile where noise levels were 8.6dB(A) higher than
compared with the level road.
(b) Buses: The average noise level for the buses travelhngon the level W surface was 75.3dB(A) and comparedwith the noise levels given for the other profiles (except forthe ramp and trench profiles) gave the highest noise level.
15
As was indicated from the car data, the higher noise levelsrecorded for the level ~ surface was Wely to be due to
the noise generated by the interaction of the tyres with theroad surface dominating overall noise levels.
For the purposes of comparing noise levels for the buses itwill be assumed that the spee~evel function derived forthe narrowest cushion, D, will approximate to the speedlevel function for the buses travelhng on a level surface of
similar type to where the speed cushions and humps were
constructed i.e. fine textured asphalt ~A). Therefore, avalue of 7 1.5dB(A) for the bus category traveling on a
level road has been assumed in Figure 10 to graphicallyrepresent the comparisons in noise levels given in Table 3.
The results show that comparing the average value derived
for each profile group (except for the ramp and the trench
profiles) the differences in noise levels at a reference speedof 25~ ranged from 0.4dB(A) higher for humps and1.9dB(A) higher for both cushion groups compared with
the estimated noise level for a level road surface of similartype. Compared with the standard deviations of between1.7@(A) to 3.9dB(A) derived from the regression analysisfor the profile groups of the individud bus types, see TablesB.3 to B.5, these differences in noise levels are not statis-
tically significant. Comparing noise levels from the profile
group representing a poorly maintained road, i.e. the trenchand ramp, showed significantly higher noise levels of78.2dB(A), about 6.7dB(A) higher than theestimatednoise
level for the level road.
In summary, therefore, average noise levels for the buses
havelfing over the various surface profiles at a reference
speed of 25ti were generally comparable with thatestimated for a level road surface of similar type i.e. fine
textured asphalt, the exception was for the poorly main-tained road profile where noise levels were, on average,
6.7dB(A) higher than compared with the fine texturedasphrdt level road.
(c) Commercird vehicles: Table 3 shows that the averageof the maximum noise levels from dl the commercialvehicles studied was 78.6dB(A) for the level profile wherethe road surface was hot rolled asphalt (~A). The corre-
sponding value for all the commercial vehicles measuredalongside the narrowest of the speed cushions, D, was78.4dB(A). As the design of this cushion was least likely toinfluence the spee~evel function for this category ofvehicle it could be argued that the spee”~evel function
derived from measurements using cushion D is representa-
tive of the corresponding spee~evel function for a level
profile where the surface is similar to the type where thecushionsfiumps were constructed. To support this view
additiond measurements using two of the commercialvehicles, V6 and V7, were carried out on a fine textured
asphalt ~A) surface similar to the surface type where thespeed cushion and humps were constructed.
The average of the maximum noise levels for these two
vehicles was 72.7dB(A) and similar to the average value of
73.5dB(A) measured for the same two vehicles on thenarrowest of the speed cushion designs, D. It is therefore
argued that the overall average of the maximum noiselevels for dl the commercial vehicles measured alongside
speed cushion design D, 78.4~(A), represents a goodapproximation to the corresponding vrdue for a level sur-
face profile similar to the type where the cushionfiumpswere constructed.
Comparing the estimated level profile noise value of
78.4dB(A) with the corresponding average noise levels foreach of the other profile groups given in Table 3 and shown
in Figure 10 indicate that on average noise levels from the
commercial vehicles traveling over the narrow cushionswere not significantly different from the noise for a level
road. However, for the wide cushions noise levels were
about 10dB(A) higher, whereas the corresponding averagevalue for the humps was about 8dB(A) higher comparedwith a level surface. The road profiles representing poorly
maintained road surfaces gave the highest levels with anaverage of 91 .7dB(A), about 13dB(A) higher than thecorresponding levels estimated with a level FTA surface.
Within each of the profile groups the noise levels associ-
ated with each design were fairly consistent except for thehumps where humpE, which was the ‘flat-top’ profile gave
significmtly higher noise levels of 90.6dB(A) compared82.7dB(A) for hump F which had a ‘round-top’ profile.
In summary, therefore, average noise levels for the com-
mercird vehicles traveling over the various surface profiles
at a reference speed of 25W were generally lower for thenarrow speed cushions compared with the other profiles
and comparable with that estimated on a level road surfacewith similar surface texture characteristics. The other pro-
files studied gave significantly higher noise levels withaverage values some 8- 10dB(A) above the corresponding
levels estimated for the level ~A surface. However, itshould be noted that hump E with the ‘flat-top’ profile gavenoise levels which were higher by some 8 dB(A) than the
corresponding levels obtained alongside hump F with the‘round-top’ profile. The profiles representing a road in poorcondition gave the highest levels which were, on average,13 dB(A) higherthm the levels estimated for the level FTAsurface and fufiher illustrates the importance of correctly
reinstating a road surface after road works have been
carried out.
3.2.2 At a speed typical for the type of roadprofde
An dtemative method for comparing noise levels for thedifferent vehicle types and profile groups is to use average
speeds which are typical for the type of road profile. Thespeeds have been derived from previous surveys whereeach of the different profile types have been installed. It is
16
anticipated that this form of comparison will give a clearerindication of the change in vehicle noise level to be ex-
pected in practice following the installation of the speedcontrol cushion or hump.
Table 4 gives the average noise levels for each vehicle
category at typical speeds associated with each profile.These values are illustrated graphically in Figure 11.
(a) Car: For the level road profile the average maximumnoise level for the car traveling at 45 ~ (28 mph) was
71 .O~(A). The results show that instrdting speed cushions
or humps would lead to substantial reductions in vehiclenoise levels in accordance with a reduction in vehicle
speed.
The average reduction in noise level for the narrow cush-ions (width less than 1700rnm) was 6.6dB(A) at a speed of
30M (19mph) whereas for the wide cushions (width
greater than 1700mrn) and humps the corresponding reduc-tions were 8.7 and 10.2dB(A) respectively for a speed of
22M (14mph). This result agrees well with measure-
ments carried out in York where for a similar change in
vehicle speeds, the average noise for tight vehicles fell by
8.4dB(A) after instating speed cushions of width 1700mm
(Abbott et d, 1995).
(b) Buses:For the level road profile the average maximumnoise level for the buses traveling at 38W (24mph) was
73.7dB(A). The results show that instdting speed cushionswould not lead to substantial changes in vehicle noise
levels as compared with the car results. For both narrow andwide cushions, where estimated bus speeds are reduced to
34W and 24H respectively, changes in noise levels
are less than 1dB(A). For the humps, where vehicle speedsare lower than for the cushions ( 18~), then bus noiselevels may be reduced by about 3.6dB(A).
(c) Commercial vehicles: For the level road profile theaverage maximum noise level for dl the commercial vehi-
cles travelhng at 38W was 79.7dB(A). The results showthat instdting speed cushions or humps would lead gener-ally to an increase in vehicle noise levels from commercialvehicles despite reductions in vehicle speeds.
Notably, wide cushions and hump E indicate substantial
increases in noise levels of 7.9 and 6.2dB(A) respectively.
Narrow cushions gave a smaller increase of about 2dB(A).
TABLE 4
Comparison of vehicle noise levels for different road profiles at typicrd road speeds
Profile code Mtimum noise level W(A) at 7.5m6
car Buses Cornrnercid vehicles
Level road (M) 45 38 38L 71.0 73.7 79.7
Narrow cushions (M) 30 34 34B 64.7 75.7 81.9c 64.0 75.1 81.9D 64.6 73.2 80.5
Average 64.4 74.7 81.8(-6.6) (+1.0) (+2.1)
Wide cushions (W) 22 24 24A 61.7 74.5 87.7I 62.2 72.5 88.9G 62.9 73.6 86.4H 62.3 72.3 87.0
Average 62.3 73.2 87.6(-8.7) (-0.5) (+7.9)
Humps (M) 22 18 18E (’flat-top’) 60.7 70.0 85.9 (+6.2)
F (’round-top’) 60.9 69.8 77.6 (-2.1)Average 60.8 70.1 81.7
(-10.2) (-3.6) (+2.0)
c Values in brackets are average differences in noise level compared with a level road. Negative values indicate reductions in vehiclenoise levels for the speeds shown in itics.
17
Average vehicle speed for each profile group/code (kM)
Level (L) 1 2 3Cars ■ 45 30 22 22
Buses w 38 34 24 18
Commercial ❑ 38 34 24 18vehicles
AWER Mde cushionsAverage for each (width > 1700mm)
profile group
BEFORELevel surface
r
Profile code: L
Profile group: 1
I2
Narrow cushions(width < 1700mm)
r
r
B
3
D A
1
G
2
Humps
E
3
Surprisingly, hump F with the ‘round-top’ profile indicatedreductions in vehicle noise levels of about 2~(A). How-ever, as shown in Figure 9, the variation in noise level withspeed for the commercial vehicle category traveling over
hump F was highly sensitive to changes in vehicle speed.For example, doubling the vehicle speed of commercialvehicles on a level surface would cause an increase in noise
of about 2~(A) whereas noise levels would increase byabout
3.3
12@(A) for the hump F profile.
EST~T~G CHANGES ~
Fig. 11 Vehicle noise levels before and after installing speed control cushions
noise levels have been developed which have been found tocorrelate reasonably well with people’s dissatisfaction withroad traffic noise experienced in their homes.
The frost scale focuses on the statistical variability of thefluctuating noise level andisthe noise level that is exceededfor 10% of the time, L~lO.This scale is generally used in this
country for environmental assessment purposes for newroad schemes (DoT, 1994), and for determining entitle-ment to noise insulation under the Noise Insulation Regu-lations (1988).
ROAD TRAFFIC NOISELEVELS
The results so far have dedt with the itiuence of differentprofile designs on vehicle noise emissions for a range ofvehicle categories. Although the results show how vehiclenoise levels change with vehicle speed for the variousprofile designs it is difficult to assess the overall environ-mental impact of road traffic noise.
In general, trfilc noise at a given location is the combined
noise from individud time-varying noise sources, i.e. vehi-cles in a traffic stream. In assessing the impact of trafficnoise on the environment two scales for describing traffic
The alternative scale, LAW,is widely used in Europe and the
USA, is concerned with the energy content of the noise andis defined as a notionrd steady noise level which, at a given
location and over a defined time period, would have thesame acoustic energy as the actual fluctuating noise.
Although these two scales are very different in describingtraffic noise, surveys have shown that for the majority ofsituations of practical interest there is a direct hnear corre-spondence between the two scales with L~10 generallyexceeding L~q by about 3~(A) (Noise Advisory Council,
1978). Therefore changes in traffic noise level will gener-
ally lead numericrdly to the same value, irrespective of thescale used.
18
In this report changes in trtilc noise levels will be esti-mated using the LAq scale because, unlike L~lO, a simple
method exists which enables changes in traffic noise levels,LAW,to bepredictedfrom estimates of the change in vehiclenoise levels for each vehicle category (Noise Adviso~Council, 1978). Details of the method used for predictingchanges in traffic noise levels Lti, are given in Appendix D.
To illustrate the influence of the changes in vehicle noise
levels described in section 3.2.2 on overall trtilc noiselevels the prediction method described in Appendix D. 1
was appfied to various traffic scenarios. Table 5 describes
the different trtilc fix assumed for each scenario. Table
6 gives the predicted change in trtilc noise levels follow-ing the installation of the vtious types of speed control
measures. The predictions assume that changes in vehicle
speeds follow those described in Table 4 and that there is nochange in overall trtilc flow or vehicle composition before
and after the cushions and humps are installed.
Although these examples can only indicate broady thechange in trtilc noise levels it is encouraging that when
apphed to a red situation, as demonstrated in the example
given in AppendixD.2, the predicted change intrtilc noisefollowing the installation of speed control cushions are ingood agreement with measured values.
Scenario 1 examines the change in trtific noise levelswhere the tr~lc consists entirely of cars. The remaining
scenarios gradudly replaces up to 26% of the cars with 1Yo
buses and 25% commercial vehicles. The objective ofchoosing this range of traffic composition was to illustrate
the dramatic reduction in traffic noise levels after installing
the various cushions and humps where the trfic composi-
tion is only cars and the i~uence on noise levels fromheavier vehicles as they are gradudly introduced into the
traffic stream. The results are also shown graphically inFigure 12,
TABLE 5
Trtilc composition for various trtilc scenarios
Scenario Percentage of vehicle type in trtilc stream
cars Buses Commercial vehicles
1 100 0 02 98 1 13 94 1 54 89 1 105 84 1 156 79 1 207 74 1 25
TABLE 6
Estimated change in trtilc noise level, LAq dB, for each trtiIc scenario
following the inst~lation of different designs of speed cushions and humps
Trtilc Estimated change* in traffic noise level, LAq dBscenario Narrow cushions Wide cushions Humps
(B,C,D) (A,I,G,H) ‘flat-top’ ‘round-top’
@) T)””
1 -4.8 -5.7 -7.12 -3.3 +0.2 -0.5 -5.33 -0.9 +5.1 4.6 -2.64 +0.3 +7.0 +6.4 -1.35 +0.9 +7.8 +7.3 -0.76 +1.3 +8.3 +7.8 -0.27 +1.6 +8.7 +8.2 +0. 1
‘Negative values indicate a reduction in trtilc noise, LAWdB.‘* Changes in trtilc noise level is hig~y sensitive to changes in vehicle speed.
19
1
2
34
56
7 L100 0
96 1
94 1
89 1
64 179 1
74 1
01
510
1520
25
Narrow Wide Flat-top (E) Round-top (F)*
cushions cushions humps humps(width < 1700mm) (width > 1700mm)
Fig. 12 Estimated change in traffic noise level after installing different ~pes ofspeed control measures for a range of traffic scenarios
● (Changea in traffic noise levels are highly sensitive to changes in vehicle spd)
3.3.1 Narrow cushions
For traffic scenario 1, where dl vehicles are cars, thereduction in traffic noise would be expectedtobe 4.8@(A)
for the narrow cushions. As the percentage of buses andcommercial vehicle are introduced into the trtilc stream
then noise level reductions become smaller and may causea slight increase in traffic noise when the percentage ofcommercial vehicles exceeds about 10~0.
3.3.2 Wide cushions
For the wide cushions, rdthough there are substantidreduc-
tions of 5.7dB(A) where the traffic consists of all cars theintroduction of even a small percentage of buses and
commercial vehicles (about 170) rapidly alters the changein noise levels. Further increases in the percentage of
commercial vehicles causes traffic noise levels to increase
rapidy by up to 7dB(A) when the percentage of commer-
cird vehicles reaches about 10YO. However, further in-
creases in the percentage of commercial vehicles to 25%only increases noise levels by a further 1.7dB(A).
3.3.3 Speed control hups
The change in trtilc noise level for the humps as thepercentage of commercial vehicles increases would appear
to be dependent on the profile shape. The performmce ofboth humps E and F on changes in noise levels where thetraffic consists of dl cars is similar to that shown for wide
cushions, i.e. a substantird reduction of about 7dB(A). Asthe percentage of buses and particularly commercial vehi-cles are introduced into the traffic stream then the perform-
ance of hump E, with the ‘flat-top’ profile, is again similar
to the wide cushions, with rapid increases in the change innoise levels as the percentage of commercial vehicles are
20
increased up to about 1090 with further increases in the
percentage of commercial vehicles to 25% only adding a
further 1.8dB(A) to the ovedl noise level. Hump F, withthe ‘round-top’ profile, differs dramatically as expectedfrom the changes in vehicle noise levels shown earfier.
Although the estimated reduction in noise level diminishes
as the percentage of commercial vehicles increases, even at
the 10% level the estimated change in noise level stillindicates a reduction of about ldB(A), not until the percent-
age of commercial vehicles exceed 25% does noise levels
begin to increase.
Generally, where the trtilc stream consists of more than10% commercial vehicles the estimated change in noiselevel becomes less sensitive to changes in the proportion of
commercial vehicles in the traffic stream. For example, inthe case of the ‘flat-top’ hump the estimated change intraffic noise level altered by about 13dB(A) as the propor-tion of commercial vehicles increased from O to 10%compared with only a further 2dB(A) change when theproportion of commercial vehicles increased from 10 to
20%.
The results of the estimated change in noise levels follow-
ing the installation of tie various speed controlling meas-
ures rehes on accurately estimating the change in vehicle
road speeds. This is particularly importat in the case of the
‘round-top’ hump where the slope in the relationship be-
tween noise and speed for commercial vehicles is large, seeTable D.2. A small error in estimating the reduction in road
speed forcornmercial vehicles, following the installation of‘round-top’ humps, may lead to significantly different
results than indicated.
4. SUMMARY ANDCONCLUSIONS
An off-road trial to examine the relationship betweenvehicle noise emissions and vehicle speed for different
categories of vehicles travelhng over a range of differenttypes of road profiles including speed control cushions and
humps was carried out using the test track facility at ~,it should be noted that the road humps/cushions were
placed on level ground, and therefore the conclusions
drawn from this study may not be apphcable where the road
is at grade. Other types of profiles were dso included forcomparison purposes. These were a trench and ramp profilewhich were specifically designed to simulate a poorly
maintained road. Level surfaces typical of normal roadconditions were dso included in this study.
A range of vehicles grouped into three categories: fightvehicles; buses and commercial vehicles; were selected for
testing. The fight vehicles consisted of a passenger car anda rnik float. The buses included a midi, a single-decker anda double-decker bus, dl fitted with air suspension. A totrd
of 6 commercial vehicles were selected with gross vehicleweights ranging from 16t to 38t. The selected commercialvehicles were chosen to be representative of the currentfleet in the UK but susceptible to generate above average
levels of body noise. All six types of commercial vehicles
had metal suspension systems.
The objective of the study was to compare the noise
emission levels from vehicles traveling over each of the
different designs of speed control cushions and humps.
Initially comparisons were carried out with the noise levels
norrn~sed for a given road speed of 25W (16mph). A
further comparison with noise levels normtised to a roadspeed typical for the particular design of speed cushion orhump was included which allowed reductions in vehicle
noise levels following the installation of the particulardesign of cushion or hump to be estimated.
A method for predicting the change in traffic noise follow-ing the installation of the different types of designs of speedcontrol cushions and humps was described and used to
estimate the change in traffic noise for different trtilc
scenarios.
The following main conclusions can be drawn from this
study:-
WHICLE NOISE EMISSIONS
Comparing noise emission levels from vehicles travelhngover the different road profiles was found to be not onlydependent on vehicle category and vehicle speed. but dso
on how the effect on different designs of road profilesinfluence speed reduction and the incidence of body noise,
particularly, for commercial vehicles.
Li@t veMcles:
1. For the passenger car, the results of the regressionanalysis of vehicle noise level with road speed showed thatfor the five different profile types, i.e. level surface, narrow
cushion, wide cushions, humps and poorly maintainedsurface (the ramp and trench), the change in noise level with
speed was essentially independent of the road profile overthe speed range 15 to 40W (10 to 25mph). Comparing
the noise level and speed functions derived from the pas-senger car traveling over the speed control cushions in theoff-road trial with similar survey data collected alongside
speed control cushions in York showed very good agree-
ment.
2. By comparing the noise levels for the passenger cartraveling over the speed cushions, road humps and trenchnorrnahsed to a speed of 25~ (16mph) it was found thatthe noise levels were similar to those obtained for a levelroad where the surface was constructed with similar texture
characteristics, i.e. a fine textured asphalt WA). For theramp profile, the noise level was 8.6dB(A) higher com-pared with the corresponding noise level obtained dong-
21
side the level ~A surface. This result illustrates the impor-tance of ensuring that after road works are carried out the
road is properly reinstated.
3. The estimated reduction in the maximum noise emis-
sion levels from cars due to the speed reductions at narrowcushions (width less than 1700mm) was 6.6dB(A) com-pared with 8.7dB(A) for the wide cushions (width greater
than 1700mm) and 10.2dB(A) for the humps. These esti-
mates compare well with results from surveys of vehicle
noise emissions carried out alongside speed control cush-
ions (width of 1700rnm) in York, where reductions of
8.4dB(A) in the noise from cars were achieved after the
cushions were installed.
4. The difference in noise levels between cushions con-structed of different matends (asphalt and moulded rub-
ber) was small (about 1.5dB(A)) and was not statistically
significant at low speeds i.e. up to 25M. In addition, thedifferences were not consistent over the different catego-ries of vehicles. The difference in noise levels between asingle cushion and two cushions in single file spaced 4mapart was dso small (up to 2dB(A)). Again, these differ-ences were not statistically significantly different at lowspeeds, and not consistent over the different categories ofvehicles studied.
5. Noise levels for the mik float were higher comparedwith the passenger car for similar average speeds of about
15ti (lOmph): differences ranged from 6.6dB(A) forthe
level road to 19.7dB(A) for the trench with the correspond-
ing values for the other profiles in the range 10.7 to14.OdB(A).
BUSW:
6. Generally, averaging the results over dl the buses, therelationship between noise level and speed for both thenarrow and wide speed control cushions were similar withthose obtained for the hump profiles. Although for indi-vidud buses the type of hump design did influence noiselevels differently. In particular, for the double-decker bus,noise levels were about 5dB(A) higher for the ‘flat-top’
hump design compared with the ‘round-top’ hump profile.
7. Overall average noise levels for the buses travelhng
over the speed control cushions and humps were highercompared with the car by between 15dB(A) at low speeds,
15H (lOmph), and by about 5dB(A) at higher speeds,40M (25mph).
8. For the profiles which were included to simulate apoorly maintained road surface (the ramp and trench) noise
levels were higher compared with the other profiles bybetween 5 to 15dB(A). Generally the differences in noisewere greater as vehicle speeds increased.
9. Comparing the average noise level for the buses trav-eling over each profile norrntised to a speed of 25~
22
(16mph) gave similarresultsto those obtainedforalevel roadwhere the surfaces were of a similar type, i.e. fine textured
asphalt. The exception was for the profiles which wereincluded to simulate a poorly maintainti road surface. (the
ramp and trench) where noise levels were 6.7dB(A) higher.
10. Generally, the results show that installing speed cush-
ions or humps would not lead to substantial changes inmaximum noise emission levels for buses. For both narrow
and wide cushions changes in noise levels are estimated to
be less than ldB(A). For humps, where vehicle speeds are
further reduced compared with the cushions, then bus noise
levels may be reduced by up to 3.6dB(A).
Commercial veficles:
11. Comparing the average spee~evel functions for eachprofile group across dl the commercial vehicles studied
over the speed range 15 to 40~ (1Oto 25mph) indicatedthat maximum noise emission levels from vehicles travel-
hng over the narrow cushions (widths < 1700mm) weresignificantly lower compared with the other profile designsapart from hump F (’round-top’ profile) where at lowspeeds, less than 20ti(12mph), noise levels were simi-lar. For example noise levels for the narrow cushions(width less than 1700mm) were about 9dB(A) lower com-
pared with the wide cushions (width greater than 1700rrun).
12. Comparing the average noise level for commercialvehicles traveling over each profile norrnatised to a speed
of 25~ (16mph) gave, for the narrow cushions, similarresults to those estimated for a level road where the surfaces
were of a similar type, i.e. fine textured asphalt. The otherprofiles gave, on average, significantly higher noise levels
ranging from 10dB(A) for the wide cushions to 8dB(A) for
the humps and 13dB(A) for the poorly maintained profiles.Noise levels for hump E (’flat-top’ profile) were, on aver-
age, 8dB(A) higher than for hump F (’round-top’ profile).
13. Results show that instdhng speed control cushions andhumps would lead generally to increases in the maximumnoise emission levels for commercial vehicles despite thereductions in vehicle speeds. For narrow cushions (widthless than 1700mrn) and humps the overall average increasewas found to be about 2. OdB(A) compared with about
8.OdB(A) for the wide cushions (width greater than1700mm). However, it was found that the ‘round-top’hump provided areductionin noise level of about 2.OdB(A),
on average, compared with an increase in noise level of
about 6dB(A) for the ‘flat-top’ hump.
14. Examining in detail the spee~evel functions for the
individud vehicles within this category showed a widevariation in the regression of noise level and speed for the
range of profile designs studied. The vehicles were chosento demonstrate possible ‘worst case’ effects since thesevehicles were known to be prone to the generation of bodynoise when driven over uneven surfaces. Therefore, it isUely that for a more representative sample of the whole
commercial fleet, noise levels would be, on average, lower
than those measured alongside the various profile designs
included in this study.
T~~C NOISE E~SSION
15. A prediction method for estimating the change in
traffic noise levels after speed control cushions and humps
are instdld was developed using the spee~evel functionsderived from the off-road trials for different categories ofvehicles. The prediction method was tested using the be-fore and after trtilc parameters from a traffic noise surveywhere speed control cushions were installed in Gde Lane,York. The predicted change in Mlc noise levels was
estimated to be 3.8dB(A) compared with a measured value
of 4.3dB(A) and were therefore in good agreement.
16. The prediction method was used to estimate the changein traffic noise following the installation of different types
of speed control cushions and humps for a range of trafficscenarios where the percentage of commercial vehicles in
the traffic stream increased from O to 25% whilst that of
buses increased from Oto 1%. It was assumed that the total
flow of vehicles before andafterthe cushion or humps wereinstalled remained the same.
17. Where the traffic stream consists entirely of cars, the
prediction model estimates that for both humps and cush-ions, traffic noise levels, dB(A), would reduce followinginstallation. For humps the reduction in trtilc noise levelswould be about 7dB(A), whilst for speed control cushions,reduction in trtilc noise levels would be about 5dB(A).
18. As the proportion of commercial vehicles in the trtilc
stream increases, the reduction in traffic noise followingthe installation deteriorates drarnaticdly, particularly for
wide cushions and ‘flat-top’ humps where tr~c noiselevels, in fact, increase by about 7dB(A) when the propor-
tion of commercial vehicles reaches about 10Yo.
19. Estimates of the changes in trfic noise levels follow-
ing the installation of both narrow cushions and ‘round-top’
humps are less sensitive to changes in the proportion of
commercial vehicles in the trtilc stream compared withthe other two designs. When the proportion of commercialvehicles reaches 1590, the change in noise level is less thanldB(A) for both narrow cushions and ‘round-top’ humps,whereas, for wide cushions and ‘flat-top’ humps, noise
levels have increased by more than 7dB(A).
20. Where the traffic stream consists of more than 109o
commercial vehicles the estimated change in noise levelbecomes less sensitive to changes in the proportion ofcommercial vehicles in the traffic stream. For example, in
the case of the ‘flat-top’ hump the estimated change intrfic noise level altered by about 13dB(A) as the propor-
tion of commercial vehicles increased from O to 10%compared with only a further 2dB(A) change when theproportion ofcomrnercid vehicles increasedtim 10to 20%.
21. The results of the estimated change in noise levelsfollowing the installation of the various speed controlling
measures reties on accurately estimating the change in
vehicle road speeds. This is particularly important in the
case of the ‘round-top’ hump where the slope in the rela-
tionship between noise and speed for commercial vehiclesis large, see Table D.2. A small error in estimating the
reduction inroad speed for commercial vehicles, following
tie installation of ‘round-top’ humps, may lead to signifi-cantly different results than that illustrated above.
The conclusions from this work are timited by the type ofvehicles included in this study, particularly with the selec-tion of commercial vehicles. All tie cornmerciat vehicles
studied were tested unladen and dl had metal suspension
systems which were prone to high levels of body noise.These vehicle were dehberately chosen to give an indica-
tion of potential problems associated with the generation of
body noise. In order to obtain a more representative esti-mate of the influence of different vehicle speed control
devices afurtheroff-road trird is being conducted at TRL to
investigate the influence of load on noise emissions from
commercial vehicles and includes a selection of vehicles
with air suspension.
It will be possible to use the spee~evel functions deter-
mined for the narrowest cushion in these off-road trials (iewidth 1500 mm) to predict changes in noise levels oncesuitable ‘before’ and ‘after’ speeds are available from testsites on the pubtic roads. The speed measurements cur-rently being carried out at the trunk road tr~lc calming
scheme on the A49 in Shropshire should give an indicationof speeds at these cushions and an opportunity to check
predicted changes in noise levels with measured values.
5. AC~OWLEDGEMENTS
The authors would like to acknowledge the assistance ofMr G J Harris with vehicle selection and of Mr M
Biddiscombe with the analysis and to also thank Rediweld
Rubber Mouldings Ltd and B T M Somerford Ltd for theuse of their rubber speed cushions.
6. MFEUNCES
ABBOTT, P G, S M P~LIPS, and R E LA_LD(1995). Vehicle and trtilc noise surveys alongside speedcontrol cushions in York. TW Project Report 103. Trans-port Research Laboratory, Crowthome, England.
B~TISHSTANDARDS INSmTION, (1985). BS 594.
Hot rolled asphalt for roads and other paved areas, Part 1.British Standards Institution, London, England.
23
BW~SH STANDARDS INS~TUTION, (1994). BS EN
60651:1994. EC 651:1975. Specification for Sound levelmeters. British Standards Institution, London, England.
DEPARTMENT OF TRANSPORT, SCO~ISH OFFICE
INDUSTRY DEPARTMENT, WELSH O~CE and DE-
PARTMENT OF ENVIRONMENT FOR NORTHERN
IRELAND (1994). Design manual for roads and bridges,Volume 11: Environmental Assessment. HMSO, London.
INTERNATIONAL STA~A~S ORGANISATION
1S0 (1964). Measurement of noise emitted by vehicles.
Recommendation R362. Intemationrd Standards Organisa-tion.
THE NOISE ADVISORY COUNC~ (1978). A guide tomeasurement and prediction of the equivalent continuoussound level Lq. HMSO, London, England.
THE NOISE ~SULATION (AMENDMENT) REGU-LATIONS 1988. Statutory Instrument 2000, HMSO, Lon-
don, England.
WEBSTER, D C (1993). Road humps for controlhngvehicle speeds. Department of Transport, ~L ProjectReport 18, Transport Research Laboratory, Crowthome,
England.
WATTS G R (1988). Case studies of the effects of trtilc
induced vibrations on heritage buildings. TRL ResearchReportRRl 56. Transport Research Laboratory, Crowthome,UK.
WATTS G R (1989). The effects of traffic induced vibra-tions on heritage buildings - ftiher case studies. TRLResearch Report RR207. Transport Research Laboratory,
Crowthome, UK.
24
APPENDIX A: PHOTOGWPHS
A.1. Test Vehicles
(a) Light vehicles
Plate 1: V1Passenger car
Plate 2: V2Milk float
(b) Buses
Plate 3: V3Midi-single decker
Plate 4: V4Single decker
Plate 5: V5Double decker
25
(c) Commercial vehicles
Plate 6: V62-axle rigid curtain-sided 16t
Plate 7: V72-axle rigid drop-sided 16t
Plate 8: V82-axle rigid box body 16t
Plate 9: V92-axle stip lorry with empty stip 16t
Plate 10: V1O3-axle rigid tipper 24t
26
Plate 11: V112-axle artic with containers 28t
L
A.2 Sutiace profiles
(a) Narrow cushions (width < 1700mm)
Plate 12: BH: 75mm, L: 2000mm, W: 1600mm
Asphalt
Plate 13: CH: 65mm, L: 3500mm, W:1600mm
Asphalt
Plate 14: DH: 60mm, L 3500mm, W: 1500mm
Asphalt
27
(b) Wide cushions (width > 1700mm)
Plate 15: AH: 75mm, L:2000mm, W: 1900mm
Asphalt
Plate 16: GH: 75mm, L: 1950mm, W: 1900mm
Moulded Rubber
Plate 17: IH: 75mm, L:2000mm, W: 1900mm2 Cushions in single file 4m apart
28
Plate 18: HH: 80mm, L: 2380, W: 1880mm
Moulded rubber
(c) Humps
Plate 19: ‘Flat-top’ EH: 75mm, L:7800mm, W: 4000mm
Asphalt
(d) Poorly maintained sutiace
Plate 20: ‘Round-top’ FH: 75mm, L:3700mm, W: 4000mm
Asphalt
Plate 21: Trench TDepth(mm): 40mm, L:l 200mm, W: 3000mm
Pl~ood
Plate 22: Ramp RVertical drop: 75mm, L:600mm, W: 4000mm
Concrete
29
TABLE B.1
Regression analysis of vehicle noise and speed for passenger car @l)
Profile code Regression analysis statisticsConst Slope Corr Std Dev
(A) (B) (r) dB(A)
Narrow cushions
B 19.7 30.4 0.98 1.1
c 29.7 23.2 0.98 0.8
D 15.8 33.1 0.99 0.7Average 21.8 28.9 0.97 1.1
Wide cushions
A 27.3 25.6 0.98 1.0
I 6.8 41.2 0.95 2.2
G 20.2 31.8 0.99 0.9H 25.8 27.1 0.99 0.6
Average 20.2 31.3 0.94 1.7
Humps
E (’flat-top’) 14.4 34.5 0.94 2.1 ‘F (’round-top’) 23.8 27.6 0.96 1.4
Average 18.5 31.5 0.94 1.8
OthersRamp R 29.3 30.0 0.96 1.3
Trench T 24.4 28.5 0.97 1.1
Level L8 17.2 33.8 0.99(17.7) (32.2) (0.98) (::1)
7 Regression analysis of maximum noise level, L. dB(A) and the logarithm of vehicle speed, V M, takes the form:
L.= A + Blog,OV dB(A)
where Const = the constant term A.Slope = the slope of the regression line B.Corr = the comelation coefficient r.
and Std dev = the residud standard deviation.
8 Value in brackets refers to regression analysis for measurements carried out on fine textured asphalt surface
30
1
TABLE B.2
Regression analysis of vehicle noise and speed, including average values,
for mik float fully laden with empty rnik bottles (V2)
~ofile code Regression analysis statistics Average vehicle
spee~evelConst Slope Corr Std Dev Vehicle Noise level
(A) (B) (r) dB(A) w) dB(A)9
Narrow cushionsB 169.7 -84.4 -0.56 7.6 15 71.3c 119.0 -38.4 -0.45 5.7 17 71.9D 63.5 1.1 0.08 0.9 16 64.9
Average 107.7 -31.7 -0.32 5.8 16 69.4 (12.8)
Wide cushionsA 46.5 23.9 0.17 12.2 17 76,0I 32.5 44.3 1.00 0.9 12 80.3G -51.0 114.5 0.87 6.4 15 83.5H 0.6 61.4 0.43 11.1 17 76.1
Average 40.6 30.6 0.45 9.1 15 79.0 (14.0)
Humps
E (’flat-top’) 76.1 -7.6 -0.10 3.4 14 67.4F (’round-top’) 26.6 31.0 0.94 0.9 19 65.9
Average 63.2 2.9 0.09 2.8 16 66.7 (10.7)
~hersRamp R 94.2 -14.5 -0.14 3.2 14 77.7 (14.0)Trench T -50.2 108.7 0.52 10.4 15 77.7 (19.7)tivel L 49.9 13.5 0.71 1.3 19 67.0 (6.6)
9 Values in brwkets refer to the difference in noise levels between the fik float and the passenger car at the indicated average speed.
Positive values indicate that the noise level for the fik float is higher than for the car.
31
TABLE B.3
Regression andysis.of vehicle noise and speed for rnidi-21 seater bus (V3)
fiofile code Regression analysis statistics
Const Slope Corr Std Dev
(A) (B) (r) dB(A)
Narrow cushions
B 60.1 9.4 0.54 2.3c 61.5 8.2 0.50 1.9D 62.7 7.0 0.46 1.9
Average 61.2 8.4 0.50 1.9
Wide cushionsA 62.1 7.9 0.53 1.8
I 62.4 7.5 0.58 1.5
G 64.5 6.8 0.42 2.0
H 61.4 8.8 0.65 1.5
Average 62.4 7.9 0.53 1.7
Humps
E (’flat-top’) 51.6 14.8 0.78 1.8F (’round-top’) 49.9 16.4 0.85 1.8
Average 50.9 15.5 0.81 1.7
OthersRamp R 51.5 21.3 0.94 1.2
Trench T 55.3 14.4 0.73 2.2Level L 56.8 12.6 0.78 1.7
32
TABLE B.4
Regession analysis of vehicle noise and speed for single-decker bus ~4)
Profile code Regression analysis statistics
Const Slope Corr Std Dev(A) (B) (r) dB(A)
Narrow cushionsB 55.5 12.6 0.72 1.9
c 55.8 12.0 0.74 1.7
D 41.3 18.4 0.94 1.1
Average 52.4 13.2 0.54 3.2
Wide cushions
A 64.2 7.0 0.46 2.2
I 37.0 24.7 0.91 1.7
G 44.8 26.0 0.82 2.4
H 29.9 28.1 0.84 3.1Average 42.9 20.6 0.70 3.3
Humps
E (’flat-top’) 37.9 21.6 0.89 1.7
F (’round-top’) 59.0 9.3 0.59 2.2Average 52.5 12.7 0.56 2.9
Others
Ramp R 39.9 27.8 0.93 1.7Trench T 58.5 12.3 0.68 2.2
Level L 56.3 13.5 0.78 1.8
33
TABLE B.5
Regression mdysis of vehicle noise and speed for double-decker bus (V5)
Profile code Regression analysis statistics
Const Slope Corr Std Dev
(A) (B) (r) dB(A)
Narrow cushionsB 72.1 3.6 0.29 1.9
c 71.6 3.6 0.36 1.4
D 56.6 13.1 0.57 2.8
Average 67.1 6.5 0.38 2.3
Wide cushionsA 77.8 -0.7 -0.06 1.8
I 73.2 0.4 0.05 1.3
G 86.3 -8.6 -0.51 2.0
H 61.9 9.3 0.51 2.4
Average 72.8 1.5 0.09 2.4
Humps
E (’flat-top’) 55.5 14.5 0.79 1.7
F (’round-top’) 47.5 16.5 0.69 2.6
Average 57.2 12.1 0.40 3.9
GthersRamp R 47.8 22.9 0.98 0.8
Trench T 66.5 8.5 0.62 1.7
Level L 66.3 7.3 0.78 0.9
34
TABLE B.6
Regression analysis of vehicle noise and speed for 2-ale rigid (V6)
Profile code Regression analysis statisticsConst Slope Corr Std Dev
(A) @) (r) dB(A)
Narrow cushionsB 46.1 25.4 0.86 2.4c 73.8 7.1 0.51 1.9D 47.3 21.0 0.73 3.2
Average 55.8 17.8 0.56 4.0
Wide cushionsA 78.1 11.7 0.52 3.0I 74.1 14.1 0.63 2.8G 81.9 8.2 0.50 2.3H 69.9 15.8 0.58 3.6
Average 76.1 12.4 0.53 3.0
Humps
E (’flat-top’) 52.4 30.2 0.96 1.5
F (’round-top’) 3.0 58.8 0.97 2.3Average 28.6 43.8 0.78 5.5
Ners
Ramp R 86.2 3.4 0.35 1.4Trench T 73.0 15.9 0.74 2.8Level L 68.3 8.2 0.82 1.1
TABLE B.7
Regression analysis of vehicle noise and speed for 2-role rigid (V7)
Profile code Regression analysis statistics
Const Slope Corr Std Dev(A) (B) (r) dB(A)
Narrow cushions
B 64.9 6.0 0.44 2.1
c 23.5 32.6 0.93 2.1D 54.6 11.2 0.74 1.8
Average 48.1 16.2 0.65 3.0
Wide cushions
A 32.0 34.7 0.89 3.0I 23.8 42.3 0.90 3.3G 29.1 35.9 0.88 3.3H 38.3 27.8 0.87 2.4
Average 32.1 34.2 0.82 3.7
HumpsE (’flat-top’) 8.0 51.9 0.97 2.1
F (’round-top’) 44.6 19.4 0.86 2.0Average 26.8 35.3 0.68 6.0
OthersRamp R 49.6 25.2 0.93 2.2Trench T 83.5 4.0 0.63 1.4Level L 65.0 9.0 0.81 1.1
36
TABLE B.8
Regression analysis of vehicle noise and speed for 2-ule rigid (V8)
Profile code Regression analysis statistics
Const Slope con Std Dev
(A) (B) (r) dB(A)
Narrow cushionsB 50.1 16.8 0.95 0.9c 50.3 16.6 0.95 0.9D 51.8 15.2 0.97 0.7
Average 50.7 16.2 0.95 0.8
Wide cushions
A 54.0 17.0 0.56 4.2
I 35.4 29.7 0.89 2.6
G 50.9 15.8 0.93 1.0
H 50.5 16.2 0.96 0.7
Average 48.8 18.8 0.66 3.3
Humps
E (’flat-top’) 8.4 52.8 0.96 2.5F (’round-top’) 50.8 16.4 0.96 0.7
Average 16.3 45.0 0.81 4.8
~hersRamp R 67.2 12.5 0.87 1.5
Trench T 56.1 20.4 0.91 1.9hvel L 60.4 10.9 0.94 0.8
37
TABLE B.9
Regression analysis of vehicle noise and speed for stip lorry with empty sbp (V9)
Profile code Regression analysis statistics
Const Slope Corr Std Dev(A) (B) (r) dB(A)
Narrow cushionsB 72.3 3.4 0.18 2.9
c 87.9 -5.2 -0.32 2.3D 69.9 7.2 0.68 1.2
Average 76.5 1.9 0.10 2.7
Wide cushions
A 61.6 19.6 0.77 2.6I 48.7 30.5 0.82 3.3G 50.2 27.8 0.81 3.2H 43.7 31.3 0.93 1.9
Average 51.4 27.0 0.79 3.1
Humps
E (’flat-top’) 36.0 40.1 0.97 1.7F (’round-top’) 5.5 60.4 0.93 3.4
Average 21.0 50.0 0.92 3.1
OthersRamp R 82.0 4.5 0.39 2.2Trench T 69.7 14.6 0.72 2.9Level L 58.7 14.0 0.82 2.1
38
TABLE B.1O
Re~ession analysis of vehicle noise and speed for 3-ale rigid (V1O)
Profile code Regression analysis statistics
Const Slope con Std Dev
(A) (B) (r) dB(A)
Narrow cushionsB 57.8 20.4 0.79 2.3
c 62.6 17.0 0.60 3.4D 64.8 14.0 0.55 2.8
Average 61.5 17.2 0.62 2.9
Wide cushionsA 53.8 23.9 0.73 3.5
I 63.1 17.7 0.80 2.1
G 58.9 20.7 0.89 1.6
H 71.2 14.1 0.69 2.4
Average 61.8 19.0 0.71 2.7
HumpsE (’flat-top’) 78.2 9.5 0.68 1.5
F (’round-top’) 61.1 16.4 0.87 1.3
Average 71.6 11.7 0.37 4.0
OthersRamp R 91.2 1.9 0.21 1.6
Trench T 101.4 -4.0 -0.38 1.8
Level L 89.3 -5.4 -0.59 1.3
39
TABLE B.11
Regression analysis of vehicle noise and speed for skeletal artic with containers (Vl 1)
Profile code Regression analysis statisticsConst Slope COK Std Dev
(A) (B) (r) dB(A)
Narrow cushions
B 60.4 19.5 0.60 4.1c 53.0 24.2 0.52 6.4D 49.4 26.0 0.58 5.9
Average 53.5 23.7 0.56 5.3
Wide cushions
A 47.4 37.5 0.68 6.4I 68.8 24.6 0.59 5.7G 39.8 42.1 0.72 6.8H 80.5 16.6 0.75 2.4
Average 59.2 30.2 0.63 5.7
HumpsE (’flat-top’) 74.4 20.4 0.86 2.0
F (’round-top’) 28.8 45.2 0.98 1.5Average 53.1 31.8 0.64 6.1
OthersRamp R 95.5 4.2 0.36 2.3
Trench T 89.4 8.2 0.42 3.7Level L 69.1 7.0 0.63 1.8
40
APPENDIX C: VEHICLE NOISE LEVEL AND SPEED FOR BUSES ANDCOMMERCIAL VEHICLES
BUSES
90
I I I
10 20 30 40 50
Vehicle speed (km)
fig. C.1 Midi single dscker bus ~3)
Narrow cushions (BCD) — — — — —(width c 1700mm)
Wde cushions (AIGH) -------(width > 1700mm)
Ramp (R) -------- ------
‘Fiat-top hump (E) —.—.—. .
‘Round-top’ hump (F)
Trench ~ -----
--1o 20 30 40 50
Vehicle speed (km)
Fig. C2 Singledecker bus (V4)
-------
.-” ----- ---
.<- -.F - /-
‘910 20 30 40 50
Vehicle speed (kti)
Fig. CS Double-decker bus N5)
41
C.2 COMMERCIAL VEHICLES
110
Narrow cushions (BCD) — — — — — ‘Flat-top hump (E) —.—. — . .
(width c 1700mm)
‘Round-top’ hump (F)Wde cushions (AIGH) -------(width > 1700mm) Trench (T) -----
Ramo (R) . . . . . . . . . . . . . .
. /“7
-“/ti*&-----
- *- F/~-d 4------------ -----------”
./.
----
------
10 20 30 40 50
Vehicle speed (ktih)
Hg. C.4 2-axle rigid curtain-sided 16t (V6)
10 20 30 40 50
Vehicle speed (ktih)
Fig. C.6 2-axle rigid box body 16t (V8)
-— --- -----. . . . . . . . . . ... . . . . . . . . . . . . . . . .
--- ----------------
----
6010 20 30 40 50
Vehicle speed (km)
fig. CA 3-axle rigid tipper 24t (V1O)
10 20 30 40 50
Vehicle speed (ktih)
Fig. C.5 2-axla rigid drop-aided 12t (W)
“o~
60 I I I
10 20 30 40 50
Vehicle speed (ktih)
fig. C.7 2-axle atip lorry with empty skip (V9)
110 I
. .&@-
“P-............/-----
10 20 30 40 50
Vehicle speed (km/h)
Fig. C.9 2-axle artic with containers 28t (Vl 1)
42
APPENDIX D: TRAFFIC NOISEPREDICTION MODEL
D.1 GENERAL
A method for predicting traffic noise using the LAWscale
was developed by a Working Party for the Technicrd Sub-
Committee of the Noise Advisory Council Noise Advi-
sory Council, 1978). This section briefly outies the method,
describes the input parameters and illustrates the method byway of an example breed on a trfilc noise survey carried
out in Gale Lane, York (Abbott et d, 1995).
D.1.l Basic equation for predicting tr~lcnoise levels, LAW.
The basic equation for predicting trtilc noise level, LAWisgiven by the following formula:
D.2 COMPAR~G MEAS~D ANDPREDICTED CWNGES ~TRAFFIC NOISE LEVELS
A vehicle and traffic noise survey was carried out along Gde
Lane, York in 1994 (Abbott et d, 1995). Traffic noise levels
we~ measured using the L~10,~~~ indexl”. Changes in noise
levels following the installation of speed control cushions
memured using this index will be similar to changes in the
traffic noise index L~w,18~~, as discussed in Section 3.3.
The first section D.2. 1 gives the values of the input param-
eters to Equation@. 1) both prior to and after the insola-tion of the speed cushions in Gde Lane. The followingsection compares the measured change in trtilc noise withthe calculated value.
D.2.1 Input parameters
r For each vehicle category, the vehicle flow (expressed as a, ,1
where N =
m=
P“ =
and L=n =
total traffic flow over a specified time
period
the number of different vehicle categories
thepercentageofvehicles inthetic streamwhich are classified as vehicle category n.
L- - lolog,ov
where L- is the maximum pass-by noise level from avehicle traveling at a speed of v H
L~“ is a measure of the total energy associated with a
single vehicle pass-by for a vehicle classified as vehicle
category n.
The find term C is a constant for a given location, sitelayout, and specified time period.
To calculate, using Equation @.1), the change in trtilc
noise level, L~q, after speed control cushions or humps areinstiled, requires the following input parameters for both
the before and after situations:
(a) the trtilc flow over a specified time period;
@) the number of vehicles in each vehicle categoryexpressed as a percentage of the total flow (Ye);
(c) the mean road speed -) for each vehicle cat-egory together with the maximum pass-by noise level,L_ti(A), at the mean road speed.
percentage of the total flow), mean speed (v W) and the
noise level L- ~(A) derived from the spee~evel func-tions developed from the off-road trials and shown in Table
D.2, are given together with the toti traffic flow over the
18-hour period both before and tier the speed control
cushions were installed.
D.2.2 Results
The design of speed cushions constructed in Gde Lane,York were similar to the speed cushion design used in the
off-roadtrids except the width of the cushions were 1700mmand therefore classified between the narrow (width lessthan 1700mrn) and wide (width greater than 1700mm)cushion designs. Predictions oftilc noise were therefore
carried out for both narrow and wide cushions and theaverage difference was then compared with the measured
change in trtilc noise level.
Table D.3 shows the results of the predicted change intrtilc noise following the installation for both the narrow
speed cushions (width less than 1700mm) and the wide
speed cushions (width greater than 1700mm) derived using
Equation Q. 1) with the input parameters given in Table
D.1.
For the narrow cushions the predicted change in trfilcnoise levels was 6.O~(A) indicating substantial reduc-
tions in tr~lc noise levels after instifing this design ofcushion.
For the wide cushions the predicted change in traffic noiselevels indicated a smaller reduction of only 1.6~(A)compared with traffic noise levels prior to the cushionsinstalled.
Comparing the average predicted change in trtilc noiselevel of 3.8~(A) with the measured value of 4.3~(A)
shows good agreement.
43
TABLE D.1
Input parameters for predicting change in traffic noise level, L~a dB.
Vehicle catego~ and trfic parametersll Before After12
Narrow cushion Wide cushion
Trtilc flow (veM18h) 11,646 10,296
cars mow (%) 94 97.8Mean speed (W) 52 28.8
L- dB(A) 73.1 64.0 65.9
Buses mow (%) 1 1.2Mean speed (~) 38 34 24
L- dB(A) 73.7 74.6 73.1
mow (%) 5 1Comrnercid Mean speed m) 38 34 24
vehicles L- dB(A) 79.7 81.8 87.6
Table D. 1 shows the input parameters used in Equation (D. 1) to calculate the change in trtilc noise due the installation
of speed cushions in Gde Lane, York.
10 The noise index L~,O,8~dB is derived from the arithmetic average of the eighteen one hour period values of L,, O,, dB over the periodfrom 06.00 to 24.00 ‘hours
11 Traffic flow and composition were derived from traffic counts taken through out the period when the traffic noise surveys took place,The mean vehicle speeds are based on traffic surveys carried out by York City Councfl. L- dB(A) values have been derived fromthe speeMevel functions shown in Table D.2.
12 The width of the speed cushions in Gale Lane were 1700rnm and hes between the widths of the narrow (width< 1700mm) and thewide (width > 1700mm) speed cushions defined in this report. Therefore calculations based on the speeflevel functions for boti tvmsof cushions have been de-fived and then averaged to give the fmd result.
. .
TABLE D.2
Regression statistics for the relationship between noise and speed fordifferent vehicle categories travelhng over different surface profiles
Vehicle Regression Average value of re~sion statistic for each vehicle -g~ and surf= pfle
categoq statistic
Level Narrow Wide
Cushions Cushions Humps
c) (BCD) (NGH) E F
car Slope 32.2 28.9 31.3 31.5Constant 17.8 21.8 20.2 18.5
Bus Slope 11.4 9.6 11.4 14.7Constant 55.7 59.9 57.4 51.6
Commercial Slope 7.5 16.8 25.1 34.1 41.3vehicles Constant 67.9 56.1 53.0 43.1 25.8
44
TABLE D.3
Comparison between measured and predicted traffic noise levels in Gde Lane, York
Change in traffic noise level for different widthof speed cushions ~(A)13
Narrow cushions Wide cushions
( width< 1700mrn ) ( width> 1700mrn )
Predicted 6.0 1.6
Average 3.8
Measured 4.3
13 Redicted traffic noise levels are based on the Lx ,W, @ index wtist tie measured value used the L~lO,l,,~ index.
45
