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Traffic calming measuresfor bus routesBus Priority Team technical advice note BP2/05September 2005

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Transport for London (TfL) continues to introducea variety of initiatives to make bus journeysreliable, quick and comfortable. Bus usage inLondon is growing at its fastest rate since 1946and bus passenger numbers are at their highestsince the 1960’s. Each day over 6 millionpassenger trips are made on a network of 8,200buses, running on roads which vary in terms ofcharacter and function.

Alongside the drive to enhance bus services is the on-going need to improve road safety. TfL supports a range of traffic calming measuresto reduce the number and severity of accidentson both the Transport for London Road Network(TLRN) and borough roads. The introduction of well designed traffic calming measures on bus routes, such as speed cushions, can improveroad safety while having little or no adverseeffect on bus passengers and services.

This technical advice note replaces ‘TrafficCalming Measures for Buses’, which waspublished in 1999. Since then, a number ofchanges have affected the operation and deliveryof bus services in London including the formationof TfL in 2000, under the control of the Mayor,and the replacement of London’s bus fleet with

fully accessible low floor vehicles. Accordingly,the previous guidelines have been fully revisedand enhanced to reflect these changes anddevelopments in traffic calming techniques.

The main changes include the acceptance of1700mm wide speed cushions on bus routes and new advice on traffic calming measures forarticulated bus services. TfL has worked closelywith London’s local authorities to develop theseguidelines, including a current trial of VehicleActivated Signs (VAS) on a bus route to assesstheir impact on traffic speeds, without the use of vertical or horizontal carriageway deflections.This complements the road safety campaignaimed at educating people to drive responsibly.

TfL and London’s local authorities continue to work together with bus operators to improveservices and these guidelines make a valuablecontribution to reconciling public transport and road safety. The London Technical AdvisorsGroup (LoTAG) and The London Bus OperatorsCommittee have endorsed these guidelines,recognising that London’s streets can be made safer for all without unduly affecting public transport.

Foreword

Peter Hendy, Managing DirectorSurface Transport, Transport for London

Barry Arnold, ChairmanLondon Bus Operators Committee

Traffic calming measures for bus routes

Gareth Davies, ChairmanLoTAG Transportation Working Group

Transport for London | 3

IntroductionIn recent years a number of new traffic calmingmeasures and bus types have been introducedresulting in a need to update TfL’s guidance fortraffic calming on bus routes. The most notabledevelopment in bus type is the introduction ofarticulated buses, which has raised issuesregarding their operation along roads wheretraffic calming measures exist.

These guidelines were produced taking intoaccount the latest research regarding buses andtraffic calming. Trials to determine suitable trafficcalming on routes used by articulated buses werecommissioned as part of this work.

It is increasingly important that traffic calmingschemes are seen as a piece of urban design, sothat they can make a positive contribution to thestreetscene. Well designed and implementedtraffic calming schemes can add dramatically tothe quality of the public realm.

The purpose of these guidelines is to provideadvice to highway authorities on how they caninstall new traffic calming measures withoutcompromising road safety or inconveniencing bus passengers. In some cases the design ofexisting traffic calming schemes may no longer be compatible with bus operation and highwayauthorities are urged to consider amending suchschemes to comply with these guidelines, in particular on routes operated by low-floor or articulated buses.

Where proposed traffic calming schemes do not follow these guidelines, particularly in termsof size and numbers of vertical measures, TfL’sRoad Safety Unit and Bus Priority Team will workclosely with the highway authority to identify anacceptable solution. Accident data and analysisshould be available to ensure that traffic calmingschemes are properly justified.

Key points1 Horizontal deflections are generally

acceptable, except on routes where articulated buses operate.

2 Speed cushions are the preferred verticalmeasure on bus routes and are acceptable in small numbers when used as part of a combination of traffic calming measures.

3 Speed tables and raised junctions areacceptable in small numbers at key locations, preferably as part of a series of traffic calming measures.

4 Care should be taken to site parking at a sufficient distance from traffic calmingmeasures to avoid hindering bus operation.

5 Round-top road humps are not acceptable on bus routes in London.

6 Trials are currently underway to assess the impact of Vehicle Activated Signs on traffic speeds along bus routes.

7 The cumulative effect of all traffic calmingmeasures must be taken into account regarding increased discomfort to drivers and passengers.

8 The measures used should be suitable for the types of buses that use the route.

9 Appendix A provides a summary of theacceptability of traffic calming measures on bus routes.

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1. Traffic calming and buses - specialconsiderationsTraffic calming schemes raise a number of specialissues for the operation of buses. The followingconsiderations should be taken into accountwhen traffic calming schemes are being designedand installed:

l buses have firmer suspension systems, similar to most other large vehicles carryingheavy loads

l buses are less manoeuvrable than cars

l bus operators have a duty of care to theirpassengers, particularly the elderly anddisabled, who may be standing or movingaround the bus

l bus operators must take into account thehealth and safety of all bus drivers. In somesituations traffic calming can cause greatdiscomfort, especially if the bus service hasnumerous vertical deflections

l traffic calming can lead to increased wear and tear to buses and where they are drivenalong a traffic calmed road many times a day this can lead to damage or increasedmaintenance costs

l bus services operate to a timetable, reliabilityis important if customer confidence is to bemaintained; and

l traffic calming schemes should not causeexcessively increased journey times to busesby requiring diversions or slowing downsignificantly more than other vehicles.

2. Road classifications associated withtraffic calmingThe design speed of traffic calming schemes canvary according to the type of road and theactivities that take place along it. The Departmentfor Transport (DfT) publishes Traffic AdvisoryLeaflets, which give advice on the effectivenessand use of various traffic calming measures in avariety of situations. These leaflets are referredto as appropriate and further details are given inthe Bibliography at the end of this document.

The IHT have published a useful reference book(see Bibliography), which includes details ofmeasures and schemes introduced and theirimpact on traffic speeds and accidents.

Local roads in residential areasWhere appropriate, a speed of about 20 mph is becoming the common target for local roads in residential areas. Sometimes this speed can be achieved by incorporating traffic calmingmeasures into a designated 20 mph zone.Alternatively, 20 mph speed limit signs androundels can be used providing vehicle speedsare already at an appropriate level (see TrafficAdvisory Leaflet 9/99 for more details). In general, the buses which operate in theseareas are ‘local services’ and they should be able to operate at 15 to 20 mph. It is advisedthat bus operators consider an operational speed of 15 mph or less when crossing traffic calming,such as speed tables, to minimise discomfort(see Traffic Advisory Leaflet 10/00).

Distributor roadsOn 30 mph distributor roads, traffic calming aims to restrict speeds to within the speed limit and to deal with specific accident sites orlengths of road. Schemes with only horizontaldeflections have been successful in somelocations. The most serious problems for busoperations have occurred where excessivenumbers of speed tables and cushions have beeninstalled on important high frequency bus routes.


3. Traffic calming techniquesThere is now a broad range of traffic calmingtechniques in use. This section considers each in turn and discusses their implication for bus passengers.

A) Visual appearanceChanging the road appearance is an importanttechnique in altering a driver’s behaviour on theroad. Drivers can be encouraged to slow down by breaking up long lengths of wide road withvisual measures such as road markings. These can be used to create an impression of anarrowing or a speed hump in the carriageway.Coloured or textured road surfacing and physicalmeasures such as bollards, islands or treeplanting can be used to change the character of the road. This can improve the highwayenvironment for both road users and residents,but due consideration should be given to cyclists.Roads in new developments should be designedto incorporate this approach.

B) Speed cameras and variable signsCameras and new technology can providealternatives to humps and other verticaldeflections. In addition to the well-known‘Gatso’ spot speed cameras, time-distancecamera equipment is being developed. Thesetime-distance cameras use number platerecognition at sites a known distance apart,allowing average speeds over lengths of road to be accurately measured. Vehicles exceedingthe speed limit can then be identified.

TfL is currently working with time-distancecamera suppliers to develop equipment suitablefor use at the boundaries to residential areas to

aid enforcement of 20mph zones. The equipmentwill be appropriate for reducing speeds on anylinear stretch of road. Trials are planned inCamden and it is hoped the equipment willreceive Home Office approval by Autumn 2006.

Vehicle Activated Signs (VAS) that warn speedingdrivers, have also been effective at specificlocations (see DfT Traffic Advisory Leaflet 1/03).The signs, which have no negative impact on busservices, are currently being trialled by TfL on a bus route to determine their effect on traffic speeds.

Islands and Hatching

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C) Access control measuresThe use of residential areas by rat-running trafficcan have a significant impact on the localenvironment. Measures, such as widthrestrictions, that restrict access to certainvehicles can minimise extraneous traffic volumes passing through an area. Bus servicescan be catered for in such schemes by installingbus gates or lanes, enforced by CCTV cameras to discourage access by other vehicles. Physicalbarriers, including rising bollards or arms, are not recommended as they can be mechanicallyunreliable and often struck by vehicles, causingoperational problems for buses.

Making changes to traffic signal staging or timingsis another way of discouraging through-traffic, or rat-running. This is not always appropriate on bus routes but where buses may be affectedmitigation measures, such as short bus lanes,should be considered (see DfT Traffic AdvisoryLeaflets ITS 5/03 and ITS 6/03). Selective VehicleDetection will also provide additional benefitfor buses.

D) Priority changesl Altered priority at junctions can benefit buses

as they do not need to queue, although thejunction’s capacity can be severely reduced(see DfT Traffic Advisory Leaflet 6/01)

l Mini-roundabouts can slow traffic on allapproaches provided there is sufficient flow on all arms. On bus routes, painted mini-roundabouts are considered preferable to those with raised central domes, whichbuses have to negotiate. Special considerationmay need to be given if articulated buses have to turn at a raised mini-roundabout tominimise passenger discomfort.

E) Horizontal deflection devicesOn bus routes, horizontal deflections (see DfTTraffic Advisory Leaflets 9/94 and 12/97) aregenerally preferred over vertical deflections as they do not produce upward jolts to buspassengers, but less pronounced sidewaysmovements. TfL recognises however, thathorizontal deflection measures alone are notalways effective at reducing speeds.



Horizontal traffic calming measures can beincorporated into hard-landscaping projects toenhance the visual appearance of a scheme. The types of measures which can be combined ina scheme include:

l Chicanes that allow two-way flow but withreduced carriageway width. Care needs to betaken to ensure that parked vehicles do notimpede buses. The trials conducted in June2004, concluded that chicanes designed toallow the passage of an articulated bus wouldhave little effect on the speed of most othervehicles. Therefore, chicanes are notrecommended on articulated bus routes

l Large central islands can be used to createnarrower carriageways (see Traffic AdvisoryLeaflet 7/95)

l Road markings such as cross-hatching andcycle lanes can be used to create a visual, but not physical, narrowing of the carriageway.

l Overrun areas can also be used to reinforce the appearance of horizontal deflections.Overrun areas are designed to help largevehicles negotiate narrowings, chicanes,roundabouts and tight corners particularly onnarrow residential roads (see Traffic AdvisoryLeaflet 12/93)

l Pinch points can calm traffic speeds byrequiring vehicles to give way to one another.One lane may have priority over vehiclestravelling in the opposite direction.Consideration should be given to providingcycling facilities, such as a cycle by-pass.

All the above measures can successfully reduce vehicle speeds. They are generallyacceptable on bus routes, although care needs to be taken to ensure that parking near chicanesand roundabouts does not impede buses andthat the geometry of measures allows longerbuses to pass.

F) Vertical deflection devicesOn bus routes, vertical deflections of anappropriate type should only be consideredwhere speeding and collision problems cannot be treated by the traffic calming measuresalready outlined above. The requirements forroad humps are given in the road humpregulations (see Traffic Advisory Leaflet 7/96).

Traffic emissions immediately near a road humpcan increase but overall emissions within a scheme can be reduced if traffic volumesdecrease accordingly (see Traffic Advisory Leaflet 2/99). Vertical deflections can also delayemergency service vehicles particularlyambulances and fire appliances (see TrafficAdvisory Leaflet 3/94).

The types of vertical deflection that can beaccepted on bus routes are outlined on pages 8-11, together with guidance for their use.

Vehicle Activated Signs

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Speed cushions are the preferred verticaldeflection measure used on bus routes, as theygenerally have less impact on buses than speedtables but slow vehicles to a desirable speed.Care must be taken to ensure that a bus canstraddle the cushion correctly, particularlywhen there are adjacent parked vehicles. For articulated buses, it is important that thereare no parked cars in the running lane, within 25 metres of the cushion. This is essential inpreventing the bus having to go ‘two wheels up’over cushions, which can be uncomfortable forbus passengers and cause delay.

Traffic Advisory Leaflets 4/94 and 1/98recommend that the side slopes of speedcushions should not be greater than 1 in 4.This is generally acceptable to TfL and busoperators, although the double rear wheels do run over the edges. More rounded profilescan be used to reduce this effect on buses. On all bus routes cushions should be amaximum of 1700mm wide (including sideslopes), 75mm high and have on/off gradients of 1 in 8 or shallower.

The spacing between the cushions in a seriesshould be a minimum of 80m. Long series ofcushions should be avoided as this will increasethe likelihood of the bus being unable to alignwith all of the cushions. Ideally, a gap of 1.5mshould be provided for cyclists between theedge of the cushion and the kerb.


Single cushionOne cushion in the centre of the carriageway canbe traversed successfully by buses. On one-waystreets, this arrangement is almost always suitable.

Two-abreast cushionsLayouts both with, and without central refuges are acceptable if there is adequate control overparking. Buses negotiating cushions can behindered by vehicles parked too close to thecushions. In the case of articulated bus routes,parked vehicles in the running lane should be atleast 25 metres from the cushions on both sidesof the road.

Two-abreast cushions with build-outsTwo-abreast cushions with build-outs is a layoutthat is suitable at many locations and, on busroutes, is preferred to three-abreast cushions.The kerb extensions can be replaced withcushions, producing three or four-abreast layouts.If parking is continuous throughout the day, thekerb extensions could be omitted but it isimportant that vehicles cannot drive throughempty parking spaces to avoid traversing the speed cushions.

Three-abreast cushionsOn many roads this layout is the simplest andcheapest to install. However, even with controlledparking on both sides of the road, buses frequentlyhave to be driven down the centre of the roadtraversing the central cushion. This is onlyacceptable where traffic flows are fairly low inboth directions, even at peak times of the day.

Single cushion

Two-abreast cushions

Two-abreast cushions with build-outs

Three-abreast cushions

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Speed tables are an extended flat-top humpwith at least a 6 metre long plateau, plus ramps.They are designed to reduce discomfort to longerwheelbase vehicles, though they do require busesto slow down more than cars. Speed tablesshould generally only be used on bus routes atkey locations, such as schools or shoppingcentres. There should not be a series of closely spaced speed tables. TfL and the busoperators would prefer no more than five speedtables on any bus route. Particular problemsoccur as the rear wheels of a bus leave the exitramp. Heights of up to 75mm are acceptable,with entry and exit ramp gradients a maximum of 1 in 20. It has been found that 12.5 metre longplateau tables are slightly more comfortable for passengers on articulated buses than 6 metrelong plateau tables though construction costsmay be greater.

l In bus only streets, where it is sometimesdesirable to use speed tables to delineatepedestrian crossing points and to moderatevehicle speeds, ramp gradients of between 1 in 20 and 1 in 30 are suitable

l In one-way streets, the exit ramps can bemade less severe than the approach ramps to assist buses leaving the speed table.

l Some authorities have used widely spacedspeed tables which have been acceptable on bus routes

l When speed tables are constructed on roadswith steep inclines care should be taken withthe design of the ramp gradients as groundingcan occur (see Traffic Advisory Leaflet 2/96).


Raised junctions are similar to speed tables but cover an entire junction, with ramps on allapproaches. They are usually flush with thefootway providing a safer crossing point forpedestrians. They can calm two streets at once,without the loss of valuable parking space, andwould be preferable to a series of speed tableson bus routes.

Rumble devices, including areas of coarse road surface texture, are generally acceptable at normal bus operating speeds. However, rumblestrips can create unacceptable noise for residentsparticularly if there are lot of strips and arelatively high volume of traffic. Resonance canoccur at slower speeds which encourages driversto increase their speed in order to reduce thevibration in the vehicle (see Traffic AdvisoryLeaflet 11/93).

Round-top road humps are not acceptable on bus routes in London as passengersexperience a double ‘thump’ when traversing the hump; one for each set of wheels.

4. Installing new traffic calmingschemesNew scheme proposals, consultation and innovationTraffic calming proposals affecting bus routes,access roads to bus garages and regulardiversionary routes should be discussed with TfLand the bus operators early in their development,so that issues can be resolved and suitablescheme designs can be agreed. This consultationshould cover the background to the scheme.Innovative designs should be used to achieve therequired level of traffic calming without adverselyeffecting bus operation. Scheme developmentcan often be assisted by first testing busoperation on the various layouts.

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Discussions at the design stage will be followedby more formal consultation at TrafficManagement Liaison Meetings and at the TrafficRegulation Order making stage. In some casesthere can be a significant period of time betweenthe initial consultation and the implementationstage. In these situations it is important toensure that any changes, such as the introductionof articulated buses, are taken into accountbefore the scheme is implemented.

Installation and maintenanceAll traffic calming should be carefully designedand installed to prevent conflicts particularly withparking, access and grounding. Special care isneeded at bus stops to ensure that access andegress is not compromised, and to reduce therisks to passengers who have just boarded or who are waiting to alight.

The quality of the construction and subsequentmaintenance should be to a high standard toensure the continuing effectiveness of themeasures throughout their life.


Bibliography

Traffic Advisory Leaflets (available on www.dft.gov.uk):3/93 Traffic calming special authorisations11/93 Rumble devices12/93 Overrun areas13/93 Gateways2/94 Entry treatments3/94 Fire and ambulance services - Traffic calming: A code of practice4/94 Speed cushions (see TAL 1/98)7/94 ‘Thumps’ thermoplastic road humps9/94 Horizontal Deflections (see TAL 12/97)7/95 Traffic islands for speed control2/96 75 mm high road humps7/96 Highways (Road humps) Regulations 19968/96 Road humps and ground-borne vibrations4/97 Rising Bollards12/97 Chicane schemes (see TAL 9/94)1/98 Speed cushion schemes (see TAL 4/94)2/99 Leigh Park area safety scheme, Havant, Hampshire9/99 20 mph speed limits and zones8/00 Bus priority in SCOOT10/00 Road humps: discomfort, noise and ground-borne vibration6/01 Bus priority1/03 Vehicle activated signsITS 5/03 Public transport priorityITS 6/03 Access control2/05 Traffic calming bibliography

Health and Safety Guidance(available on www.hse.gov.uk/vibration/index.htm)

London Cycle Design Standards, Transport for London,May 2005(available on www.tfl.gov.uk/cyclingdesignstandards)

Traffic Calming Techniques, The Institution of Highwaysand Transportation, January 2005

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Type of measure


Appendix A – Summary of measure types, bus operation, and acceptability

Appearance and perception

Change in road surfacetexture

Fully supported, althoughnoise generated by somesurface textures should beconsidered

As appropriate (using chippings of 14mm maximum size)

Coloured road surfacing Fully supported As appropriate

Street bollards, planters,trees, traffic islands,pedestrian refuges to narrow road

Generally appropriate,particularly when benefits topedestrians accessing busescan be achieved

As appropriate. Spacing must allow for parking not to be obstructive

Speed measurement devices

Vehicle activated signs Fully supported As required to improve safety

Safety cameras Fully supported As required to improve safety

Bus operation Acceptable numbers,dimensions, and spacing

Priority changes

Altered priority Fully supported althoughpriority should be given tobus route if possible

As appropriate, with busroute given priority in themajority of cases

Mini-roundabouts Generally supported althoughany raised central sectionsmust allow buses tonegotiate easily

Occasional rather than a series is preferred to avoidunnecessary side to side movements along alength of road. Cumulativeeffect may need to beconsidered.

Horizontal deflections

Road markings Fully supported As appropriate

Kerb extensions including busboarders

Usually supported,particularly at bus stops. Must allow room for busesto pass

Numbers as appropriate to road characteristics

Large central islands Usually supported.particularly at bus stops. Must allow adequate roomfor buses to pass.Consideration of effect ofadjacent parking essential

As appropriate


Vertical deflections

Chicanes Generally supported althoughroom must be given to allowbuses to manoeuvre. Mustnot be obstructed by parkedvehicles. Should not be usedon articulated bus routes

Supported in small numbersat key accident sites,although care has to be takenwith dimensions to ensurethat a smooth ride ismaintained, particularly ondouble-deck buses

Pinch points Generally supported,particularly on roads with lowtraffic flows where queuesare not likely to develop inthe opposite direction

Supported in small numbersat key accident sites althoughcare has to be taken not to cause unnecessary delayto buses

Speed tables Acceptable where no othermeasures are suitable.Cumulative effect of allmeasures must be taken intoaccount

Up to five speed tablesacceptable on a route: Up to 75mm high, 1 in 20maximum on/off gradient,6000mm long flat top but12500mm for articulated bus

Speed cushions Acceptable where verticalmeasures are necessary.Cumulative effect on a busroute has to be taken intoaccount. Cars must not beallowed to park within 25metres of a cushion and caremust be taken in the detaileddesign of layouts

Up to ten sets of cushionsper direction acceptable witha minimum of 80m spacingpreferred in a series.Cumulative effect of allmeasures should beconsidered on bus routes.Height max: 75mm. Widthmax: 1700mm including sideslopes of 1 in 4 max. On/offgradient of 1 in 8 max

Rumble devices including‘Rippleprint’

Generally acceptable,although noise considerationshave to be taken into account

Maximum height of 15mmbut lower heights can beused when combined withother measures

Round-top humps Not acceptable on Londonbus routes

Type of measure Bus operation Acceptable numbers,dimensions, and spacing

Bus Priority TeamTransport for LondonWindsor House, 42-50 Victoria StreetLondon, SW1H 0TLTel 0845 300 7000

Website: www.tfl.gov.uk

Further information For further details or advice on the use of trafficcalming measures on bus routes, contact:

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