C 1 Highway Design

7/30/2019 C 1 Highway Design

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MINISTRY OF SCIENCE AND TECHNOLOGY

DEPARTMENT OF TECHNICAL AND VOCATIONAL EDUCATION

DEPARTMENT OF CIVIL ENGINEERING

CE 3017-HIGHWAY AND TRAFFIC ENGINEERING

(SAMPLE QUESTINS AND SOLUTIONS)

SEMESTER I

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SAMPLE QUESTIONS

CHAPTER 2

HIGHWAY PLANING

1. (a)What is the object of highway planning? Write down the planning requirements.(b) Explain the items which would be included in the Road Inventory2. Explain the methods of counting vehicle volume.3. Explain the Origin and Destination Survey.

CHAPTER 3

HIGHWAY LOCATION

4. Explain the highway plans and highway specifications.CHAPTER 4

DESIGN CONTROL AND CRITERIA FOR HIGHWAY DESIGN

5. Define the following terms:a) Flow or Capacity

b) Concentration or Densityc) Average Annual Daily Traffic (AADT)d) Average Daily Traffice) Peak Hour Trafficf) 10th, 20th, 30th highest hourly volume

6. Write down the short notes on the followinga) Traffic projection factor

b) Design Volumec) Design Hourly volume

7. Write down the short notes on the followinga) Theoretical or maximum Capacity

b) Mean journey speed and mean running speedc) Spot speedd) Time mean speed and space mean speed

8.(a) An OD survey carried out to determine the current traffic on a section of a highway

revealed an ADT of 5000 vehicles in the year 1960. It is proposed to improve the

highway to cater for the needs of traffic in 1980. From a travel forecast of the area, the

Normal traffic growth is found to be 52% of 1960 traffic. Generated traffic on the basis ofpervious experience in the area estimated to be 22%. Information revealed that an

increase of 2000 vehicles trips per day is expected by 1980 due to development traffic

calculate the ADT in 1980 Local studies show that the ratio of DHV to ADT both two

ways is 15% and are one way volume in the predominant direction is 60% of two way

DHV. Calculate DHV in 1980.

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(b) The OD survey curried out to determine current traffic on a section of four-lane two-

way. Data obtained from OD survey are as follows:

No. of days Volume/ 16 hours day in 1996

1 4180

2 4270

3 43004 4470

5 4870

6 5050

7 5240

It is proposed to improve the highway to cater for the nee of traffic in 2017. From

travel forecast of the area, the NTG is 45% of 1995, the GTG is 25%. Information reveals

that there is an increase of 2000 vehs trip/day due to the development traffic. Calculate

the DHV for predominant direction in 2017. The thirtieth hour factor is 18% and volume

in the predominant direction is 70% of two-way DHV.

9. (a) TRRL MethodMON TUE WED THU FRI SAT SUN AVG

JAN 418 421 417 429 439 392 394 409

FEB 430 442 450 450 465 416 391 434

MAR 440 447 455 457 478 443 424 449

APR 456 464 476 489 501 467 452 472

MAY 471 487 493 506 527 492 506 497

JUNE 488 505 515 520 530 521 486 509

JULY 508 524 542 545 587 582 562 550

AUG 530 531 551 547 572 558 521 544SEPT 508 513 518 527 552 546 539 529

OCT 468 479 478 491 509 470 428 474

NOV 446 459 468 472 490 434 402 453

DEC 454 464 468 473 488 436 462 463

AVG 468 478 485 492 515 470 456

On a rural road, traffic volume over 16 hours were recorded,

Wednesday 7th march, 1974 5850 vehs:

Thursday 8th march, 1974 5700 vehs:

Friday 9th march, 1974 5950 vehs:

What would be the predicted traffic on an average weekday in August 1990, assuming

an annual growth rate of 5%.

(b) Data for traffic spot speeds were detained by Enoscope over a base line of 200 feet.

Stop- watch time t (sec) 2.6 2.8 3.0 3.4 3.6

Number of vehicles 11 27 62 52 34

Determine (a) Time mean speed

(b) Space mean speed.

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10. Spot speed data from collecting at a short distance of roadway are given below. Analysesare made by graphical method. Determent the design speed, maximum speed limit,

minimum speed limit and then theoretical (or) maximum capacity of this roadway.

No of

vehicles

Spot Speed (mph) No of vehicles Spot Speed (mph)

2 53 19 45.2

3 51.5 20 43.0

3 49 22 40.1

5 48 21 35.5

8 47.6 20 34.3

8 46.4 18 32.7

11 45.6 16 30.0

12 45 9 26.2

14 49.2 8 23.1

15 48 5 20.917 461 2 18.2

CHAPTER 5

HIGHWAY GEOMETRIC DESIGN

11.(a) Write down the assumption for analyzing of Passing Sight Distance.(b) Drive the formula for determining passing sight distance for a two lane highway.

12.Define the Stopping Sight or Non-passing Sight Distance. How to calculate the stoppingsight distance for a highway?

13.(a) What are the design controls for horizontal alignment design?(b) What are the design controls for vertical alignment design?14.Derive the formula for calculating the rate of super elevation on the horizontal curve.15.Explain the method of providing super-elevation by revolving the road surface about the

crown-line of the road in second stage with neat sketches.

16.Explain the method of providing super-elevation by revolving the road surface about theinner edge of the road in second stage with neat sketches.

17.Explain the types of vertical curves with neat sketch.18.Derive the formula for determination of highest point on summit curve.19.Drive the formula for determination of lowest point on valley curve.20.(a) Calculate the stopping sight distance for a road for which the design speed is 30 mph.

The coefficient of fiction between the road surface and tires may be taken as 0.4 and thereaction time of the driver may be assumed as 3 seconds. The road way is level.

(b) Calculate the passing sight distance for a road for which the design speed is 30

mph. The rate of acceleration of the first moving vehicle may be taken as 2.5 mph/sec

and the different in speeds between the overtaking and the overtaken vehicles as 10

mph.

21.(a) Calculate the stopping sight distance for a road for which the design speed is 30 mph.the coefficient of friction between the road surface and tires may be taken as 0.4 and the

reaction time of the driver may be assumed as 3 seconds. The road way is level and the

brake efficiency is 40%.

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f

VdascedisBrakingtheGiven

30tan 2

where, d = breaking distance in feet

v = speed of vehicle in m.p.h.

f = coefficient of friction

(b)Calculate the non-passing sight distance required on a highway with a design speed of60 mph, assume f = 0.42. Also assume reasonable values for other items involve in

calculation.

22. (a) Determine the minimum non-passing sight distance that should be provided for avehicle coming down a 6% gradient. Give the following data.

Design speed V = 35 mph

sV

driveroftimeaction sec35

140Re

Coefficient of friction between type road surface = 0.5

(b)Cuts of a two lane highway have a back slope of 1:2 (1 horizontal: 2 vertical) andthe grade line is level. Calculate the distance required between the centre of the roadand the toe of the cut slope to satisfy the horizontal sight distance on a circular

curve of radius of 1910 feet. The eye is assumed to be 4.5 ft above the road surfaceand the object is also 4.5 ft high. Assume

Design speed of the road = 40 mphReaction time of driver = 2 seconds.

The coefficient of friction of the road = 0.6 with the safety factor of 2.0Horizontal and curve length are the same.

23. (a) A jeep catching up a slow moving truck a two lane highway on which the designspeed is 40 mph. the jeep is traveling at the design speed and the distance between thejeep and truck is 120 feet. The driver of the jeep saw the slow moving truck suddenlybrakes to a stop. Jeep driver is so alert that his reaction time is 2.5 sec. is the braking

distance of the truck is 120 feet. Will the jeep be able to stop in time without colliding thetruck? Use coefficient of friction of 0.6. Assume the road is level.

(b) A deer is running across the level road and a driver did his best to avoid hitting this

deer by attempting to stop his car. However, during the braking, his car slided from the

concrete pavement to the gravel shoulder but finally came to a halt safely. If the travelingspeed of this car is 100 kph and coefficient of friction on the concrete pavement is 0.252,

then what should be the coefficient of friction on the gravel shoulder?Assuming that the lengths of skid marks on concrete pavement and gravel shoulder

are 100m. and 50m., respectively. Reaction time is 0.5 sec.

24.Sketch the longitudinal profile and show the stationing of key points along the roadway.Assume that the side friction is neglected and the super elevation is obtained by revolvingthe road surface about the center line or crown. The following data are given:

Design speed V = 40 mph Degree of Curve D = 8 Width of the pavement =b = 24 Amount of normal crown = c = 3

The road is passes through the open flat country, maximum super-elevation runoffis 1:150

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Normal crown ends at station 20+0025.Degree of curve = 8

Design speed V = 40 mph Width of the pavement b = 24 Amount of normal crown c = 3

15

1,supmax max eelevationerofrateimumAllowable

Allowable maximum super- elevation runoff 1: x = 1:200Normal crown ends at sta: 20+00. Sketch the longitudinal profile. Assume f is

neglected and full super elevation is obtained by revolving about the centre line or

crown.

CHAPTER 2 (from semester II)

DRAINAGE AND EROSION CONTROL

DRAINAGE AND DRAINAGE STRUCTURES

26.(a) Describe the requirements of the good road drainages system.(b) Describe the causes of change in moisture content.

27.Describe the major causes of erosion and controlling method for a highway engineer.28.Describe the side ditches, curbs and gutters for surface drainage.29.Describe the intercepting drains, pipe drains, inlets, catch basins and manholes for surface

drainage.

CHAPTER 8 (from semester II)ROADSIDE DESIGN

30. Draw the guardrails and median barriers for roadside design.

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SOLUTIONS

1. (a)What is the object of highway planning? Write down the planningrequirements.

(b) Explain the items which would be included in the Road Inventory

Solution:

(a ) Object of Highway Planning

The object of highway planning is to provide a highway system which would give

maximum transportation facilities a minimum cost. For this purpose, a well defined

programme to collect data and analyze the existing conditions is most essential

Planning Requirements

Highway planning would include.

(1)Collection and tabulation of the formation about the existing transportationfacilities in the area.

(2)Determination of the general inter-relation of all branches of the transportationsystem and their effect on each other.(3)Determination of the adequacy or otherwise of the existing facilities as per

present needs and the improvements and extension of these facilities for

anticipated future needs for a certain period.

(4)Finding out the methods for financing these projects and the periods overwhich the construction can be spread.

(5)Estimating of the cost of construction and maintenance.(b)Items which would be included in the Road Inventory are:

(1)Clear demarcation of different states in the country from roadway point ofview.

(2)Man-made and natural features adjacent to the road. e.g. buildings, landlines,fence-lines, monuments, bench marks, water courses etc.

(3)Description of the geometrics of highway such as roadway width, right of waywidth, sight distance, curve dial, gradients and road camber etc.

(4)Information about the structural components of the pavement, surface type andthe pavement design, its cross section and soil characteristics.

(5)Roadway condition, i.e. conditions of surfaces, drainage and riding qualitiesetc.

(6)Detail information about the type of drainage, structures, their location,number of spans, lateral clearance, distance between roadway surface and

stream bed, width of the structures, vertical clearance, load-capacity, condition

of structures, adequacy of waterway and the approach alignment.(7)Railroad crossings, their names, number of rail tracks, gradients of thehighway at approaches, angle of crossings, property of sight distance,

curvature if any, near it.

(8)Land-use, agricultural and other potential periodicity.(9)Classification of the highway and its service to community.(10) Traffic volume, speeds and accident experience on the road.(11) Maintenance cost of the highway etc.

2. Explain the methods of counting vehicle volume.

Volume of traffic using a section of road can be measured by counting vehicles

passing a fixed point in both directions.

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Manual methods

In this method, the passing of a vehicle is recorded by an enumerator a specially

prepared form or on a series of hand tallies, the vehicles being simultaneously classified

into a number of predetermined groups. For many purposes, it is usual to convert the

actual numbers of vehicles into equivalent passenger car unit (p. c. u); these values beingdetermined by the relative effects of different types of vehicles on traffic flow. Since the

effect of a bus or heavy commercial vehicle in a traffic stream varies according to the

precise road and traffic conditions, it is not possible to give general value to suit all

purposes.

On account of the labor involved in the conducting of a manual count, the period of

counting has generally to be limited to a few days. Observations are usually made over

the 16 hr-period from can 6am to 10pm and should preferably continue over several

consecutive days.

Since traffic flow varies from month to month throughout the year, the volume count

should be taken at the busiest time of the year.

Automatic Methods

The passing of vehicle can be recorded automatically by special equipment used in

conjunction with some form of vehicle detector. The type most commonly used is a

pneumatic detector, which consists of a length of thick walled rubber tubing about in

internal diameter fastened down to the surface of the road perpendicular to the direction

of the traffic. The passage of a vehicle axle over the tube transmits a pressure pulse

through the tube which operates an electrical contact on a diaphragm switch, so actuating

a counter which is arranged to register every other pulse in order to correspond to one

count per vehicle.

Automatic methods of counting have the advantage that little attendant labor is required,

particularly with the more elaborate type of counters, and therefore measurements can be

made for long periods. Such counters are thus ideally suited for the continuous

measurement of seasonal and annual trends at the selected sites.

The chief advantage is that these counters are not able to give a classification break down

and therefore the results must generally be supplemented by a sample manual count.

Other disadvantages are that errors can be incurred with multi-axle vehicles and also with

light vehicles such as pedal cycles which may fail to register when using pneumatic

detector tubes.

3. Explain the Origin and Destination survey.

Solution

Origin and Destination Survey

An O.D Survey is necessary where it is anticipated that traffic will be drawn from a

number of existing routes onto a new or improved road. By means of this type of survey it is

possible to estimate the number of drivers traveling on each of the existing routes who will

choose to use the new road in future.

The O.D survey obtains, in addition to straight forward count of vehicles on each

road, further information concerning the place of origin and destination of each journey and

the location of any intended intermediate stops within the survey area.

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Survey Stations must be established on all the main roads entering and leaving the

area concerned, so forming a cordon or screen line. Sites for these stations should be on

straight, level sections of road with good visibility.

There are a number of basic method by which the required information may be

obtained, namely

(1)By roadside interview.(2)By the use of prepaid postcards(3)By attaching colored tags or stickers to vehicles(4)By observing vehicle registration numbers(5)By selective interview at home or at the place of employment

1) By roadside interviewIn this method vehicles are stopped and the drivers are questioned as to the origin

destination of the journey and the location of proposed intermediate stops.

The sampling technique may be carried out on either a numeral or a time basis, but in all

cases the system should be prearranged and used consistently. One method is to stop

every nth vehicle, whilst another is to stop all vehicles arriving within certain fixed time

limits. Both methods have the disadvantage that queues may form during times of heavyflows and a third method which involves stopping the next vehicle arriving after the

completion of successive interview may be preferred. In all cases, at least two people are

required, one to carry out the interviews and one to count and direct traffic, and after it

may prove advisable to use more than one interviewer.

(2) By the use of Prepaid Postcards

This system is to hand each driver a business reply-type prepaid postcard. Questions

asked by the interviewer are tabulated and the driver is requested to answer these and also

supply the additional information concerning the type of vehicle and number of passengers

before returning the card by post to the survey headquarters

(3) By attaching colored tags or stickers to vehicles

At the incoming survey station, a tag of distinctive color is stuck on the wide screen

of each vehicle entering the survey area, a different color and shape being used at each point.

Observers at the outgoing survey stations note the color designation for each vehicle leaving

the survey area, and, if desired, other observers at selected points within the area may be used

to help trace the routes followed by the vehicles.

(4) By observation vehicle registration number

The methods mentioned above all suffer from the disadvantage that vehicles have to

be stopped to some extent. An alternative method in which the registration numbers of

vehicle passing the survey station are noted avoids these disadvantages.

To work effectively in heavy flows, two observers are required; one reading the

registration numbers of passing vehicles and the other nothing them down. Alternatively asingle observer can record the information into a portable type recorder.

(5) By selective interview at home or at the place of employment

In this method, a random sample of population is interviewed either at home or at the

place of employment to obtain information concerning details of all journeys made by the

person of family concerned on a particular day or days.

4. Explain the highway plans and highway specifications.Solution

Highway plans

In general, the plans contain the engineering drawings of the project whereasthe specifications present the written instructions.

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After the final location for a given project has been completed, including the

field soils investigation the data are forwarded to the design office. There a complete

scheme for the road is worked out by the specialist in the fields of geometric design,

drainage, structures, soils and pavements. All the dimensional features and many

other details of each final design are recorded on a series of drawings commonly

refers to as plans. Figure shows one sheet of plans for a typical two lane ruralhighway. Other sheets of plans show roadway cross-sections fitting every situation in

the entire project. Figure is typical. Also included will be sheets of drawings for all

structures and roadway appurtenance. A partial list of subjects covered by the

standard would include pipe culverts, concrete box culverts, guard rails and parapets,

curbs and gutters and curb returns, sidewalks, drainage inlet and outlet structures of

numerous types, manholes, riprap and other devices used for bank protection, fences,

and right of way and other permanent survey markers.

Highway specifications

Specifications can result in the use of improper materials and poor

workmanship. On the other hand, specifications are too exacting results in higher cost.Specifications contain the written instructions highway projects and outline carefully

and detail the procedures and the methods to be followed for each operation. Often

they are divided into two parts: standard specifications and special provisions. The

standard specifications apply to every project constructed by the agency and treat

subjects that occur repeatedly in the agencys work. The special provisions cover

subjects peculiar to the projects and in question and include additions or modifications

to the standard specifications. The special provisions issued by some highway

agencies include copies of all the documents required for securing competitive bids

and for the contract. This is helpful to both contractor and construction engineer.

5. Define the following terms:a) Flow or Capacityb) Concentration or Densityc) Average Annual Daily Traffic (AADT)d) Average Daily Traffice) Peak Hour Trafficf) 10th, 20th, 30th highest hourly volume

Solution

a) Flow or Capacity

The number of vehicles passing a point in a unit time.b) Concentration or Density

The number of vehicle traveling over a unit length of highway at a specified

instant in time.

c) AADT. (Average Annual Daily Traffic)

The total yearly volume divided by the number of days in the year.

d) ADT (Average Daily Traffic)

The total volume during a given period divided by the number of days in that

period.

No. of days Traffic VolumeDay 1 x1

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Day 2 x2

Day n xn

AADT =n

xn

n =365-366

ADT =n

xn n= 7, 14

e) Peak Hour Traffic

The highest number of vehicles found to be passing over a section of a lane or

a roadway during 60 minutes.

f) Tenth, Twentieth, Thirtieth etc. Highest Annual hourly Volume

The hourly volume on a given roadway that is exceeded by 9, 19, 29 etc,

respectively hourly volume during a designated year.

6. Write down the short notes on the following

a) Traffic projection factorb) Design Volumec) Design Hourly volumed) Theoretical or maximum CapacitySolution

a) Traffic projection factorThe future needs of traffic over a period of 20-25 years, which is taken as the

normal life of a highway, it is essential to know the development of traffic and its

ultimate value at the end of the design period. The design period is usually taken as 20

years.

It is not possible to project traffic to some future year exactly but a reason ably

accurate value can be arrived at by considering the following elements

Current traffic, made up of

(i) Existing traffic: and(ii) Diverted traffic.

Increase in traffic due to

(iii) Normal Traffic growth:(iv)

Generated Traffic growth.(v) Development traffic growth

Traffic Projection Factor

0.1

100

(%)%%1

100

,%1

DTGGTGNTGTPF

trafficcurrenttorespectwithDTGandGTGNTGoftheofsum

b) Design VolumeTraffic studies on highway both in rural and urban areas have shown that the

traffic volume varies considerably in volume throughout the day and even a greater

fluctuation in hourly volumes is indicated during a year. So it is essential to determine

which of the hourly volumes should be used for design since such a situation arises,

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only once a year and the rest of the period during the year, such a situation does not

arise. At the same time the hourly volume used for design should not be exceeded

very often during the year. It has been established that where only motor traffic is

involved, the design should be based upon the 30th Highest Hourly Volume (30 HV)

s y 29 hourly volumes in a year.

for highway catering for motor traffic only should

30th Hour factor (k)

both taken t

esearch lab method

ection (or) in both direction for two lane or three-lane during a

al (or) Maximum Capacity (Qmax) can be expressed by headway-lationship.

o that this volume of traffic is exceeded onl

c) Design Hourly volume,DHVDesign hourly volume to be takenbe the 30th highest hourly volume.

The DHV may be repressed as a percentage of ADT (or)

wo ways. DHV for future needs can be estimated by

(a) Traffic projection factor method and(b) Transport and Road r

d) Theoretical or maximum CapacityThe maximum number of vehicles which has passing over a given section of a lane or

roadway in one dir

given time period.

The theoreticspeed re

2053.004.120 VVmax

5280VQ

here acity in veh/hr

V = speed in mph

ey speed and mean running speed

c) Time mean speed and space mean speedd and mean running speed

from traffic control measures and congestion being

time.

Mean r

rsown the vehicle without actually stopping it will still be included .]

b) Spo

or new facilities. Spot speeds are

. Hence the

o measure

ll vehicles. Vehicles should be selected at random from the traffic stream.

w Qmax = Maximum Cap

7. Write down the short notes on the following

a) Mean journb) Spot speed

Solution

a) Mean journey spee

Mean journey speed

It is derived from measurement of journey time between two points a known

distance apart, delays arising

included in the journey

unning speed

It is reduced by a moving observer in the same manner as the mean journey

speed, except that all the periods of time when the vehicle is actually stationary are

deducted from the total journey time. Delays caused by congestion and other factowhich the slow d

t speed

It refers to the speed of vehicle at one particular instant of time at a specified

location. Spot speed has a variety of uses. They can be used as evidence regarding the

effect of particular traffic flow construction such as intersection and bridges. They can

be used for geometric design purpose or improved

also used in determining enforceable speed limits.

Spot speed measurement should be conducted so as to reduce a minimum

influence of the observer and his equipment upon the values obtained

observer and equipment should be located as in conspicuous as possible.

It can be measured directly by various methods and is not possible t

a

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c) Time mean speeds and space mean speedTime M

rithmetic mean of speed of vehicles passing a point during a given

ithmetic mean of speed of vehicles on a given length of road at an

stant

erages speed or space mean speed Vs is given by:

ean Speed

It is an a

interval of time.

Space Mean SpeedIt is the ar

in in time.

The difference between the two can be illustrated by considering a set of

vehicles spaced a uniformed distance apart along an infinite length of road and all

moving at the same speed V1 together with a second set of vehicles superimposed in

the first and also speed uniformly, but moving at a constant speed V2 in speed

measurements are made on all vehicles within the fixed length L of road at a

particular instant of time, then the av

.... nms

where, there are m vehicle

....21 VmV

V

s moving at speed V1 and n vehicles at speed V2 within this

oving at speed V2. Therefore, the average speed or time mean

eed VT is given by:

length at any given time.

Suppose that instead of measuring the speed of all vehicles within the fixed

length L, measurements are made on all vehicles passing a fixed point during a time

interval t. There will be mt V1/L vehicles in this time moving at speed V1 and nt V2/ L

vehicles in this time m

sp

...

...

21

22

21

21

21

1

nVmV

nVmV

L

ntV

L

mtV

L

ntV

L

mtV

VVT

8. (a) An OD survey carried out to determine the current traffic on a section of a

highway revealed an ADT of 5000 vehicles in the year 1960. It is proposed to

improve the highway to cater for the needs of traffic in 1980. From a travel forecast

of the area, the Normal traffic growth is found to be 52% of 1960 traffic. Generated

traffic on the basis of pervious experience in the area estimated to be 22%.

Information revealed that an increase of 2000 vehicles trips per day is expected by

1980 due to development traffic calculate the ADT in 1980 Local studies show thatthe ratio of DHV to ADT both two ways is 15% and are one way volume in the

redominant direction is 60% of two way DHV. Calculate DHV in 1980.

section of

four-lane t s:

No. of

p

(b) The OD survey curried out to determine current traffic on a

wo-way. Data obtained from OD survey are as follow

days Volume/ 16 hours day in 1996

1 4180

2 4270

3 4300

4 4470

5 48706 5050

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7 5240

ur factor is 18% and volume in the predominant direction is 70% of two-

way DHV.

olution

(a)

Generated traffic growth = 22%

It is proposed to improve the highway to cater for the nee of traffic in 2017.

From travel forecast of the area, the NTG is 45% of 1995, the GTG is 25%.

Information reveals that there is an increase of 2000 vehs trip/day due to the

development traffic. Calculate the DHV for predominant direction in 2017. Thethirtieth ho

S

Normal traffic growth = 52%

%401005000

2000 xtraffictDevelopmen

Sum of the traffic growth = 52+22+40 =114

14.2100

1 114

100

%%%1)(

DTGGTGNTGTPFfactorprojectonTraffic

ence ture A T (198

irections

= ADT (1980) x 30th hour factor (k)

H fu D 0) = TFP x ADT (1960)= 2.14 x 5000 = 10700 vehicles

Two-way DHV in 1980 provided the traffic is equal in both d

hourpervehilcesx 1605

100

10700 15

DHV in 1980 in the predominant direction

hrvehsx /:963100

1605 60

r say the design may be carried out for 1000 vehicles per hour

(b)

o

7

524050504870447043004270418

1995

n

XADTADT ncurrent

= 4626 vehs/16 hrs

DTG = 2000veh trip/day

NTG = 45%, GTG = 25%

1004626

2000x

= 43.23%

X 2017 in the predominant direction = 0. 7 x DHV2017 in both direction

k = 18%

% in predominant dir. = %

DHV2017 in the predominant direction = ?

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1323.2100

23.4325451

100

%%%1)(

DTGGTGNTGTPFfactorprojectonTraffic

ADTfuture = TPF x ADTcurrent= 2.1323 x4626veh/16hr day

DHV2017 in both direction = kxADT2017

=0.8x9864= 1776= 1224veh/hr

9. (a) TRRL Method

MON TUE WED THU FRI SAT SUN AVG

JAN 418 421 417 429 439 392 394 409

FEB 430 442 450 450 465 416 391 434

MAR 440 447 455 457 478 443 424 449

APR 456 464 476 489 501 467 452 472

MAY 471 487 493 506 527 492 506 497JUNE 488 505 515 520 530 521 486 509

JULY 508 524 542 545 587 582 562 550

AUG 530 531 551 547 572 558 521 544

SEPT 508 513 518 527 552 546 539 529

OCT 468 479 478 491 509 470 428 474

NOV 446 459 468 472 490 434 402 453

DEC 454 464 468 473 488 436 462 463

AVG 468 478 485 492 515 470 456

On a rural road, traffic volume over 16 hours were recorded,

Wednesday 7th

march, 1974 5850 vehs:

Thursday 8th


Friday 9th


What would be the predicted traffic on an average weekday in August 1990,

assuming an annual growth rate of 5%.

(b) Data for traffic spot speeds were detained by Enoscope over a base line of 200 feet.

Stop- watch time t (sec) 2.6 2.8 3.0 3.4 3.6

Number of vehicles 11 27 62 52 34

Determine (a) Time mean speed(b) Space mean speed.

(a) Solution

1974 1974 1990

March August August

Available) (Required)

Best estimation of average weekdays traffic in March 1947 is

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dayhrvehiclesx

ADTyADT

dayhrvehiclex

isAugustintrafficweekdayofaverageestimationBest

dayhrvehiclesxx

xx

n

16/953,14685010

51

1

16/6850449

5445654

1974

16/5654478

449

5950457

4495700

455

4495850

3

1

16

19741990

(b) Solution

Time t (sec) no. of veh. V (ft/sec) mV12

mV1

2.6 11 76.92 65083.55 846.12

2.8 27 1.42 137722.04 1928.34

3.0 62 66.67 275583.11 4133.54

3.4 52 58.82 179909.20 3058.64

3.6 34 55.55 104917.28 1888.7

Total 186 763215.18 11855.34

(a)

Time mean speed, VT

...

...

21

2

2

2

1

21

211

nVmV

nVmV

L

ntV

L

mtV

L

ntV

L

mtVV

VT

mphft 79.43sec/38.6434.11855

18.763215

(b)

Space mean speed, Vs

mphftnm

VmVVs 36.43sec/74.63

186

34.11855

....

....21

16


17/49

10. Spot speed data from collecting at a short distance of roadway are given below.

Analyses are made by graphical method. Determent the design speed, maximum speed

limit, minimum speed limit and then theoretical (or) maximum capacity of this

roadway.

No ofvehicles

Spot Speed (mph) No of vehicles Spot Speed (mph)

2 53 19 45.2

3 51.5 20 43.0

3 49 22 40.1

5 48 21 35.5

8 47.6 20 34.3

8 46.4 18 32.7

11 45.6 16 30.0

12 45 9 26.2

14 49.2 8 23.115 48 5 20.9

17 461 2 18.2

Solution

Speed Class Interval

hourpervehilcesn

RCI 49.3

258log322.31

2.1853

log322.31

Speed class

(mph)

Avg:

speed

(mph)

No of vehs: frequency Commutative

frequency

15-18.9 17 2 0.78 0.78

19-22.9 21 5 1.94 2.75

23-26.9 25 17 6.59 9.31

27-30.9 29 16 6.20 15.51

31-34.9 33 38 14.73 30.24

35-38.9 37 21 8.14 38.38

39-42.9 41 22 8.53 46.91

43-46.9 45 87 33.72 80.6347-50.9 49 45 17.44 98.07

51-54.9 53 5 1.94 100.0

total 258

17


18/49

Minimum speed limit = 15 percentile speed = 30.5 mph

Medium speed limit = 50 percentile speed = 44 mph

- to determine the maximum capacity

hrveh

xx

x

VxV

VQ

/1323

8.47053.08.4704.120

8.475280

053.004.120

528022max

11.(a) Write down the assumption for analyzing of Passing Sight Distance.(b) Drive the formula for determining passing sight distance for a two lane

highway.

Solution (a)

Assumptions;

(1)Speed of overtaken vehicles is considered as uniform along the road and equal to (V-m) mph.

(2)Passing is accomplished by accelerating during the entire period.(3)A passing (overtaking) vehicle is forced to travel at the same speed as the overtaken

vehicle before overtaking.

(4)The opposite vehicle appears at the instant where the overtaking maneuver begins andit travels at the design speed V mph.

(5)The driver of the passing vehicle requires a short period of perception time to takeover the situation.

18


19/49

For two lane highways, passing sight distance represents the sum of these distances.

Passing right distance D = d1 + d2 + d3

Where d1 = Distance traveled by the vehicle A from its position A1 during the perception

time to taken by the driver of A to decide whether or not he should be taken over

the slow moving vehicle B.

d2 = Distance traveled by the vehicle A from its position A1 to its position at A2

during the actual overtaking time t

d3 = Distance traveled by the vehicle C from its position C1 to its position at C2during the time in which the overtaking operation is completed (i.e. overtaking time t)

Let, V = design speed for the road in mph.

M = difference in speeds of the fast moving vehicle A and the slow moving vehicle

B in mph.

v, m = the corresponding values of V and m respectively in ft/sec.

a = Rate of acceleration during the overtaking maneuver in mph/sec, during the time interval

of t seconds.

a = the corresponding rate of acceleration, in ft/sec2

t = time interval in seconds to complete the actual overtaking operation.

S = Average speed of vehicles in the positions when they are closet just before and just after

the overtaking operation; and is usually called the headway

to = the perception time during which the driver of vehicle A gauges the situation, watches

the opposing traffic, gets the signal from the vehicle moving ahead and decides to

overtake.

It has been observed that the value of S so calculated is in excess of the actual

spacing between vehicles in such a case. In general,

- S in ft = Speed of vehicle B in mph + length of the vehicle in ft

S = (V-m) + 20 feet

- The perception time t0 is assumed as 2 seconds since most of the drivers can

visualize the whole situation within this period. The distance d1, d2, d3 may then be calculated

as under.Distance d1: Distance d1 = 1.47 x (V m)x t0 in feet

= 1.47 (V-m) x 2 in feet

OR d1 = 2.94 (V-m) feet

d2 = 2s + the distance covered by the slow moving vehicle in time t

OR d2 = 2s + 1.47 (V-m) x t in feet

The distance d2 can also be calculated by another method, is by considering the

distance traveled by vehicle A with an initial speed of (V m) and an acceleration a in time

t all taken in the same system of units.

Assuming, for the time being, the speed in feet/sec distance in feet and time in

seconds,

This distance covered by the vehicle A is given by

19


20/49

feetintxVddceDis

mphinaandondintwherea

St

mphintakenisrateonacceleratiifNow

a

St

staor

stmvtatmv

equaitonfromstxmvdalso

tatxmvd

47.1;tan

sec/''sec'',,73.2

sec/.

'

4

22

1

2)(2

1)(

)9(:2

2

1

33

2

2

2

2

2

The passing sight distance D = d1 + d2+ d3 for two lane highways.

12.Define the Stopping Sight or Non-passing Sight Distance. How to calculate thestopping sight distance for a highway?

Solution

Analysis of stopping sight distance

Reaction time and Breaking time.

(a) Reaction time

The time elapsed between the instant when the danger was first realized up to the

instant just before starting applying the brakes.The reaction time depends upon the physical and mental ability and alertness of the

driver. If can be divided into two parts.

(1)Perception time and(2)Foot reaction time

(1)Perception timeThe time that further elapses between the moment that the danger was first realized

and the moment the message is conveyed to the foot of the driver to take action.

(2) Foot reaction time

The time that further elapses between the moments that the foot is removed

from the accelerator and place on the brake paddle is known as foot reaction time.

Then,Reaction time = Perception time + Foot Reaction time

(b) Reaction Distance

The distance traveled by the vehicle during the reaction time is called the

Reaction Distance.

If V is the speed in mph and t, the reaction time in seconds, then the distance

covered during. The reaction time called the Reaction distance is given by

feettxVtxVx 47.160

88

Braking Distance

20


21/49

The distance which the vehicle covers from the time of application of brake while

moving of the design speed to the time when it comes to a stop is called the Braking

Distance.

It can be determined by two methods.

1st

method - From considerations of the coefficient of friction of the vehicles tires againstthe road surface.

2nd method - From considerations of the efficiency of the vehicle.

1st method - The Breaking distance may be calculated as under.

Let D = Breaking distance in feet after application of brakes

f = Coefficient of friction between the tires and the road surface

v = Speed of the vehicle at the time the brakes are applied (in ft/sec)

W = Weight of the vehicle in lbs.

g = Acceleration due to gravity (32.2 ft/sec2)

Then, on a level surface, the force along the surface = W x f

Work done by the vehicle in the distance D before stoppingunder this force = W x f x D

Work done = the difference in the kinetic energy

2

2v

g

W

Equation (1) and (2)

systemfpsin

fg

vD

v

g

WDfW

2

2

2

2

If the speed of the vehicle has to be taken in m.p.h

i.e. V = mph, then the formula (3) becomes

gradeonGf

VD

roadlevelonf

VD

gf

VD

)(30

30

2

47.1

2

2

Take + ve sign for uphill

- ve sign for do untilWhere D is in feet and V in m.p.h

2nd Method

Let D = Braking distance in feet

= Efficiency of vehicle brakes in percent

v = Speed of the vehicle at the time the brakes are applied (in ft/sec2)

-g = Deceleration rate due to gravity (32.2 ft/sec2)

Assumed with 100% efficient brakesThe vehicle moves from a speed of v ft/ sec to a stop in distance D feet.

21


22/49

Also deceleration produced by brakes with an efficiency of

Then the bodies in motion

2sec100

ftg

V2 U2 = 2as

Where, V = final speed

a = rate of acceleration

s = distance covered

100/30

100/247.1

)5(;..

100/2

10020

2

2

:

2

22

VDor

gVD

becomesequhpmVif

g

vD

Dxgn

V

n

Where D is in feet and V is in m.p.h.

13.(a) What are the design controls for horizontal alignment design?(b) What are the design controls for vertical alignment design?

Solution

Design Controls for Horizontal Alignment

(1)Alignment should be as directional as possible.(2)Use of maximum radii of curvatures should be made for the prescribed design speed

since that leads to uniform speeds and greater safety.

(3)Surprise elements e.g. sharp curvature after easy alignment, should not be introducedand consistency of design maintained as far as possible.

(4)On high and long embankments, only that curves should be used and to safeguardagainst any emergency, properly designed guard-rails should be provided.

(5)Reverse curves which introduce abrupt reversal in the direction of motion of thevehicle should be avoided.

(6)Horizontal and vertical alignment should be properly coordinated in order to give auniformly of design for safe operation.

(7)Curve approaches to the bridges should be avoided.(8)Sites for rail-road crossings must be carefully selected and curved approaches to such

crossings avoided.

Design control for the vertical alignment design

g) Short lengths of steep grades and numerous breaks should be avoided.Instead, it is perfectible to have a grade line with gradual changes

consistent with the topographic features of the area by making use of

standards laid down for gradients in a manner that gives the feeling of a

continuous line

h) Sudden, hidden and unexpected dips are undesirable since they presenthazardous situations.

22


23/49

i) Two vertical curves in the same direction separated by a short section ofa tangent grade should be generally avoided.

j) Where the length of a grade line is sufficiently great, it is preferable toprovide steeper grades of the bottom of an up grade and go on making it

milder till the top is reached, instead of making it a uniform sustained

gradek) Separate lanes should be provided for slow moving traffic when the

length of the road along any particular grade exceeds the initial length

conveniently negotiable by slow traffic

l) Where the highways meet at grade and they run at steep to moderategradients, it is better to reduce the gradient near and at the crossing to

decrease the chances of accidents.

14.Derive the formula for calculating the rate of super elevation on the horizontalcurve.

SolutionMaximum allowable rate of super elevation

Super elevation may be defined as the raising of the outer edge of the road along a

curve in order to counteract the effect of centrifugal force, in combination with the friction

between the road surface and tires developed in the lateral direction.

Let the road curve be super elevated at the rate of one in e and let the inclination of

the plane of the surface to the horizontal be .

Then,

tan = e.

let W = Weight of the vehicle in lbs acting vertically downwards.

v = Speed of the vehicle in feet/sec at the curve.

R = Radius of curvature in feet.

f = Lateral coefficient of friction between the road surface and tires.

R = normal reaction of the road on the road surface

23


24/49

The centrifugal force (C.E) acting in the outward direction ,2

gRWv

where g is the acceleration due to gravity in ft/ sec2

cossin2

WgR

WvNNRRactionThe

RL

Force of friction along the surface of the road acting down incline tending to partially

the effect of the C.F shall be equal to f R

cossin

2

gR

Wv

WRf

Substituting the value of R from equation (11) in equation (12) we have,

gRfv

fgR

v

e

gRfv

fgR

v

fgR

v

gR

fv

gR

vf

gR

fv

WgR

WvW

gR

Wv

2

2

2

2

22

22

22

1

1

tancos

sin

cossin1

sincoscossin

sincoscossin

Since, the value of f is very low, the factor fv2/gR in the denominator may be ignored for all

practical purposes

24


25/49

gR

vfe

fgR

ve

2

2

This is the relation between the rate of super elevation, the coefficient of friction, the designspeed and the radius of the curve.

.)13(exp ratiolCentrifugacalledisequationingR

VensionThe

OR

R

V

gR

Vfe

2.32

47.1

47.1

2

2

feV

RORR

Vfe

1515

22

Where V = design speed in mph

If f is neglected and V is taken as 0.75 of the design speed, we have

R

VeelevationSuper

15

75.02

15.Explain the method of providing super-elevation by revolving the road surfaceabout the crown-line of the road in second stage with neat sketches.

Solution

Method of Providing Super-elevation

The super elevation at the curves is provided in two stages:

1st stage: Neutralizing the camber of the road gradually and bringing it to straight line

slope.

2nd stage: Increasing the slope of this line gradually till design super elevation is

attained

The 1st

stage involves the rotation of the outer slope of camber about a pivot point, thelevel of which is kept constant throughout the length till the camber is neutralized.

After the surface becomes a straight fall, full super elevation is gradually achieved by

any of the following two methods:

1st method- In the1st method, the surface of the road is rotated about the crown (pivot

point)

2nd method- In the second method, surface of the road is rotated about the inner edge

of the road.

25


26/49

26


27/49

27


28/49

16.Explain the method of providing super-elevation by revolving the road surfaceabout the inner edge of the road in second stage with neat sketches.

Solution

Method of Providing Super-elevation

The super elevation at the curves is provided in two stages:

1st stage: Neutralizing the camber of the road gradually and bringing it to straight line

slope.

2nd stage: Increasing the slope of this line gradually till design super elevation is

attainedThe 1st stage involves the rotation of the outer slope of camber about a pivot point, the

level of which is kept constant throughout the length till the camber is neutralized.

After the surface becomes a straight fall, full super elevation is gradually achieved by

any of the following two methods:

1st method- In the1st method, the surface of the road is rotated about the crown (pivot

point)

2nd method- In the second method, surface of the road is rotated about the inner edge

of the road.

28


29/49

29


30/49

17.Explain the types of vertical curves with neat sketch.Solution

Types of vertical curve

Summit curves andValley curves

30


31/49

Summit curves

The major factor affecting the design of summit curves is the sight distance

across the summit since it is essential that an obstruction on the other side of the

summit whether stationery or in motion must be visible to the driver on this side of

summit and vice versa.

Summit curves are required to be introduced at the situations where,(1)A positive grade meets a negative grade(2)A positive grade meets another milder positive grade(3)A positive grade meets a level stretch(4)A negative grade meets a steeper negative grade

Valley curves

The problems of seeing across the road on both sides do not exist. Valleycurves are required to be introduced at the situation where

(1)A negative grade meets a positive grade(2)A negative grade meets a milder negative grade(3)A negative grade meets a level stretch(4)A positive grade meets a steeper positive grade

31


32/49

18.Derive the formula for determination of highest point on summit curve.Solution

Highest Point or the Summit Point on the curve

Sometimes the highest point on the curve is required to be located

a. If the gradients on either side of the point of intersection are equal, the highest pointlies on the bisector of the angle between the two grades.

b. If the gradients on either sides of the point of intersection are unequal the highestpoint lies on the side of the flatter grade.

The calculations for location can be made as under.

Let Xh be the distance AD of the highest point C on the curve measure d along the x

axis from the start of the curve on the steeper grade and yh be its ordinate from the

first grade line and equal to QC.

32


33/49

Let the distance CD is denoted by :z

Lggg

xOR

LG

gx

xL

Ggthen

G

LaPut

a

xgei

zerobeshoulddx

dzthencurvetheonhighesttheiscifNow

a

xxgZ

a

xxgQCQDZCD

equationstwoabovetheFrom

xgQDAlso

a

xyQCThen

h

h

h

h

h

h

h

h

h

h

h

h

.

.

0,,2

02

..

,

21

1

1

1

1

2

1

2

1

1

2

The distance xh is measured from the start of the curve on the side of the steeper grade

and the highest point lies on the side of flatter grade.

33


34/49

19.Drive the formula for determination of lowest point on valley curve.Solution

Lowest point on the curve

Sometimes the lowest point on the curve is required to be located. It is essential in the

valley curves, since if any gutter-gratings are fixed at any other point, the water may collect

on the curve during the rainy season and damage the road. Its position may be located asunder.

(a).If gradients on either side of the points of intersection are equal, then the lowest pointlies on the bisector of the angle between two grades.

(b).If the gradients on either side of the point of intersection are unequal, then the lowestpoint lies on the side of the flatter grade. The calculations can be made as

Fig. 5.19 Determination of lowest point on valley curve

Let xL be the distance AD of the lowest point C on the curve measured along the x-axis from

the start of the curve on the steeper grade and yL be its ordinate from the 1st grade line equal t

QC in Figure,

Let the distance CD be denoted by z.

LxgQDAlso

b

xyQCThen

1

2

11

From the above two equations,

bxxgZ

b

xxgQCQDCD

LL

L

L

3

1

3

1

If C is the lowest point on the valley curve, then dz/x should be zero

34


35/49

21

1

1

2

12

2

21

3

1

2

2

02,

.2

3

03

gg

gxor

L

G

gx

G

Lgx

xLGgThen

G

LbPut

b

xg

L

L

L

L

L

The distance xL is measured from the start of the curve on the side of the steeper grade

and the lowest point lies on the side of the flatter grade.

20.a) Calculate the stopping sight distance for a road for which the design speed is30 mph. The coefficient of fiction between the road surface and tires may be

taken as 0.4 and the reaction time of the driver may be assumed as 3 seconds.

The road way is level.

(b) Calculate the passing sight distance for a road for which the design speed is

30 mph. The rate of acceleration of the first moving vehicle may be taken as 2.5

mph/sec and the different in speeds between the overtaking and the overtaken

vehicles as 10 mph.

Solution

(a) Design speed V = 30 mph

Coefficient of friction f = 0.4

Reaction time t = 3 seconds

Then Reaction distance = 1.47 V t

= 1.47 x 30 x 3 = 132.30 ft

feetx

x

f

VceDisBraking 75

4.030

3030

30tan

2

Stopping Sight Distance = Reaction distance + Braking Distance

= 132.3 + 75 = 207.3 feet

which may be round of f to 200 ft.

Solution

(b) Design Speed, V =30 mph

Difference in speed, m = 10 mph

Rate of acceleration, a =2.5 mph

V m = 30 10 = 20 mph

Assume the perception time, t0 = 2 seconds

d1= 1.47 (30 -10) x2 =58.8 feet

Spacing between the vehicles S = 20 + (V m )

=20 + 20 = 40 feet

35


36/49

Time of overtake, t =5.2

73.2 S

=

5.2

4073.2 x=6.6 second

d2 =1.47 (V- m) x t + 2.5

=1.47 (30 10 ) x 6.6 + 2 x 40

=270 feet

d3 =1.47 x V x t =286 ft

Passing sight distance = d1 + d2 +d3

=58.8 + 270 + 286

=614.8 ft, say 600 feet

21. (a) Calculate the stopping sight distance for a road for which the design speed is 30

mph. the coefficient of friction between the road surface and tires may be taken as 0.4

and the reaction time of the driver may be assumed as 3 seconds. The road way is leveland the brake efficiency is 40%.

f

VdascedisBrakingtheGiven

30tan 2

where, d = breaking distance in feet

v = speed of vehicle in m.p.h.

f = coefficient of friction

(b) Calculate the non-passing sight distance required on a highway with a design speed

of 60 mph, assume f = 0.42. Also assume reasonable values for other items involve in

calculation.

Solution (a)




Then Reaction distance = 1.47 Vt

= 1.47 x 30 x 3 = 132.30 ft

Feetx

x

f

VceDisBraking 75

4.030

3030

30tan

2

Stopping Sight Distance = Reaction distance + Braking Distance= 132.3 + 75 = 207.3 feet

which may be round of f to 200 ft.

Solution




Road is level

Then Reaction distance = 1.47 Vt

= 1.47 x 60 x 2 = 176.4 ft

36


37/49

feetx

x

f

VceDisBraking 71.285

42.030

6060

30tan

2

Stopping Sight Distance = Reaction distance + Braking Distance

= 176.4 + 285.71 = 462.11 feet

22. (a) Determine the minimum non-passing sight distance that should be provided for a

vehicle coming down a 6% gradient. Give the following data.


sV

driveroftimeaction sec35

140Re

Coefficient of friction between type road surface = 0.5

(b) Cuts of a two lane highway have a back slope of 1:2 (1 horizontal: 2 vertical) and the

grade line is level. Calculate the distance required between the centre of the road and the toe

of the cut slope to satisfy the horizontal sight distance on a circular curve of radius of 1910

feet. The eye is assumed to be 4.5 ft above the road surface and the object is also 4.5 ft high.

Assume- Design speed of the road = 40 mph

- Reaction time of driver = 2 seconds.

- The coefficient of friction of the road = 0.6 with the safety factor of 2.0

- Horizontal and curve length are the same.

Solution (a)



Reaction time of driver =

V

35

140secs

=3535

140

= 2 secs

Gradient downhill G = 6 %

Reaction distance = 1.47Vt

=1.47x35x2 = 102.9 ft

The Braking distance =)(30

2

Gf

V

,using negative sign in the formula since the gradient is

downhill

= )06.05.0(30

352

=92.8 ft

Non-passing sight distance =102.9+92.8 = 195.7 ft adopt: 200feet

37


38/49

Solution (b)

Radius of circular curve = 1910 ft

Design speed = 40mph

required horizontal sight distance on horizontal curve = SH = 2 2)(2)5( mRR

-However, safe stopping sight distance =SH =reaction distance +braking distance

=1.47vt +f

v

30

2x S.F

= 1.47 x 40 x 2.0 +6030

2)40(

xx2.0

=295.38 ft

-But, SH = 2 2)(2)5( MRR

-Taking square on both sides, SH2 = 4[(R-5)2 (R-m) 2]

SH2 =4[(1910-5)2-(1910-m) 2]

4

2SH

= (1905)2-(1910-m) 2

(910-m)2= (1905)2-4

)38.295( 2

1910- m = 1899.27~ 1900

m = 10 ft

Minimum distance required between the centre line of the road and the toe of the cutsiope is 7.75 feet.

38


39/49

.

23.(a) A jeep is catching up a slow moving truck a two lane highway on which the

design speed is 40mph, the jeep is traveling at the design speed and the distancebetween the jeep and truck is 12 feet. The driver of the jeep saw the slow moving

truck suddenly brakes to a stop. Jeep driver is so alert that his reaction time is 2.5

sec. If the braking distance of the truck is 120 feet. Will the jeep be able to stop in

time without colliding the truck? Use coefficient of friction of 0.6. Assume the road is

level.

(b) A deer is running across the level road and a driver did his best to avoid hitting

this deer by attempting to stop his car. However, during the braking, his car slided

from the concrete pavement to the gravel shoulder but finally came to a halt safely.

If the traveling speed of this car is 100 kph and coefficient of friction on the concrete

pavement is 0.252, then what should be the coefficient of friction on the gravel

shoulder?Assuming that the lengths of skid marks on concrete pavement and gravel shoulder

are 100m. and 50m., respectively. Reaction time is 0.5sec.

Solution (a)

Stopping sight distance of the jeep = reaction distance+ braking distance

f

VV

3047.1

2

Design speed, V= 40 mph

Reaction time, t = 2.5 secCoefficient of friction, f = 0.6

ftx

xxcedissighStopping 2366.030

)40(5.24047.1tan

2

Available length between the jeep and truck = 120 +120 =240 ft> 236 ft

Therefore the jeep will be able to stop in time without colliding with the truck.

Solution (b)

Level road, G = 0 %

V = 100 kph

39


40/49

Lengths of skid marks on concrete pavement = 100 m

Lengths of skid marks on gravel shoulder =50 m

t = 0.5 sec

f for the concrete pavement = 0.252

f for the gravel shoulder = ?

d =f

VV

254

2

2

2

1

100 =252.0254

1002

2

2

x

V

V2 = 60 kph

50 =f

VV

254

2

3

2

2

50 =xf254

060 22

f = 0.283

Therefore friction coeff: for the gravel shoulder, f = 0.283

24.Sketch the longitudinal profile and show the stationing of key points along the roadway.Assume that the side friction is neglected and the super elevation is obtained by

revolving the road surface about the center line or crown. The following data are given:

Design speed V = 40 mph Degree of Curve D = 8 Width of the pavement =b = 24 Amount of normal crown = c = 3 The road is passes through the open flat country, maximum super-elevation

runoff is 1:150

Normal crown ends at station 20+00Solution

Degree of curve, D = 8

Design speed, V = 40 mph

Width of pavement, b = 24 feet

Amount of normal crown, c = 3

ftxbxeelevaitonerofamountTotal

x

xe

RceelevaitonerofRate

DRccurvecirculartheofRadius

212124sup

12

1

25.71615

4075.0

15

75.0sup

25.7168

57305730

22

40


41/49

In this problem, full super-elevation has to be reached at the start of the circular curve

Rc = Rc, Ls = Le

Finding out the length of the transition curve,

015

sup..

1501.2

1

sup

15025.7168/15

)40(15.3

8

15

4040

150

40

15040

160515.3

3

3

s

s

s

c

s

LUse

givenasrunoffelevationerallowableei

LESrunoffelevationerAvailable

ftx

L

VemphVSince

hourpervehilcesCR

VL

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25.Degree of curve = 8 Design speed, V = 40 mph Width of the pavement, b = 24 Amount of normal crown, c = 3

15

1

,supmax max

eelevationerofrateimumAllowable

Allowable maximum super- elevation runoff 1: x = 1:200Normal crown ends at sta: 20+00. Sketch the longitudinal profile. Assume f is

neglected and full super elevation is obtained by revolving about the centre line

or crown.

Solution

Degree of curve, D = 8

Design speed, V = 40 mph

Width of pavement, b = 24 feet

Amount of normal crown, c = 3

)(

15

1

12

1

25.71615

4075.0

15

75.0sup

25.7168

57305730

22

allowablex

xe

Rc

VeelevaitonerofRate

DRccurvecirculartheofRadius

use max. allowable rate of super elevation =15

1

ft

x

xe

e

VR

e

900

15115

4075.0

15

75.022

In this problem, full super-elevation has to be reached before the start of the circular

curve

c

eCR

VL

315.3

8

15

4040

150

40

150

Vc

'1205.1199008

4015.315.3

33

xx

CRVLc

e

Full super elevation = e x b = ftx 6.12415

1

Super elevation runoff = )(120

1

150

1

120

8.02

1

allowableLe

SE

Use super elevation runoff =200

1

Revised Le=200x0.8=160ft

Finding out the length of spiral curve,Ls

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(a) From the properties of transition curve

LsRc= LeRe

'20125.716

900160

x

R

RLL

c

ee

s

(b) From the consideration of the rate of radial acceleration ,c

ftx

xx

CR

VL

c

s150

25.71615

84015.315.3 33

Use max. Ls = 201ft.

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26.(a) Describe the requirements of the good road drainages system.(b) Describe the causes of change in moisture content.

Solution

(a)Requirements of the good road drainages system

A good drainage system for highways would require:

(i) Sufficiently wide and deep side-ditches to carry away all water that accumulates therein,

to some drainage structure. Water level in these ditches should remain at all times below the

sub grade level.

(ii)Sufficiently wide end deep off-take and outlet ditches to carry the water that is brought tothem.

(iii) Adequate crown along the center-line of the road to drain off quickly the water that falls

on the road-surface without allowing it to percolate.

(iv) All springs and underground sources of water to be tapped and the water drained by sub-

surface drains.

(v) Where the topography is such that the water flows towards the roadway itself, It is

essential to construct intercepting drains parallel to the road but outside the road limit to

intercept water before it reaches the road.

(vi) All drainage structures should be adequately designed to drain off water immediately

without overflowing.

Solution

(b) Causes of Change in Moisture Content

Moisture content of subgrade soil changes due to a number of causes. They can be

enumerated as:

1. Seepage of water into the subgrade from higher ground adjacent to theroad.

2. Rise or fall in the level of the water table.3. Percolation of water into the subgrade through cracks on the road surface

of through previous road surfaces.4. Transfer of moisture to or from lower soil layers by suction.

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5. Transfer of moisture either to or from the soil in the verges as a result ofdifference in moisture content.

6. Transfer of water vapor through the soil.The net result of the change in the moisture contents of the subgrade soil is the

decrease in the stability and consequent settlement of the subgrade, which causes

either total of partial failure of the road structure.At situations where frequent changes in the moisture content of t he soil are

encountered, design of a suitable subsoil drainage system is necessary. For this

purpose, it is essential to know the soil types and thick-nesses of various layers, the

position of water table if it is close to the formation and the position of the seepage

zones.

27. Describe the major causes of erosion and controlling method for a highway

engineer.

Solution

Avery vital problem that confronts a highway engineer is that of erosionoccurring due to the running water. Soils of the type that lack cohesion are most

susceptible to the effects of flowing water. In case the velocity of flow is high, every

soil will get eroded and the problem of the controlling erosion will arise.

The major cause of erosion is the capacity of water to transport fine solid

material in suspension and to roll the bigger solid particles along with it. This capacity

increases with the increase in the velocity of flow. Thus, the solution to control

erosion lies in keeping the velocity of flow within safe limits.

Of special importance to a highway engineer is the problem or erosion of

drainage ditches, side slopes of cuts and fills of shoulders adjacent to the paved

portion of the roadway. Sometimes, the streams cut in on the right of way or even

cross the highway.

There are only two ways of controlling erosion namely the control of the

velocity of flow and the use of non- erodable materials. The first method is cheaper

than the second one, which is mostly employed for the urban roads.

Prevention of erosion of the side slopes in cuts and fills is achieved by

intercepting the water before it flows down these slopes. This will involve the

construction of intercepting drains, spillways and outlet- drain to drain the water into

a natural channel. Where the soil and rainfall characteristics are such that grass or

weeds can be grown to cover the side slopes every effort should be made to cover the

surface with such small plants. The roots of these plants will spread in the soil below

and will hold the particles together. The velocity of flow will also be reduced.To limited extent special types of drainage structures can be constructed to

minimize the stream erosion and thus aid in the control of erosion along a highway. A

drop- inlet type of culvert, for example, has proved very useful in place of an ordinary

culvert, for controlling erosion. The reservoir of still water preserves the slit of fine

material that settles down due to sedimentation and can be taken out from time to

time.

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28. Describe the side ditches, curbs and gutters for surface drainage.

Solution

Side Ditches for Surface Drainage

Side ditches are used along the roadway in cuts and on ground that is fairly level andsometimes adjacent to embankments to prevent road water from flowing over cultivated of

otherwise improved land. These ditches are usually V- shaped or trapezoidal. However, the

trapezoidal ditches have a greater capacity.

One essential requirement of kutcha ditch design is that the safe velocity of flow

should never be exceeded otherwise it may create erosion. And, it is essential to ensure that

the slope of the ditch in the longitudinal direction is sufficient to drain off water quickly,

otherwise it may lead to ineffective arrangement. Side ditches should also be lined if possible

financially.

Curbs and Gutters

Curbs and gutters are essential for the city streets to drain off the storm water quickly and

to maintain the cleanliness required. Usually a kerb and gutter combination is employed for

the purpose. Sometimes, separate kerb and gutters are employed for draining off water from

the city streets. The kerb and gutter combinations are fixed at the edge of the roadway and

gullies are placed at suitable intervals. The water from the gutter flows through the grating

into the gully and is drained off through an outlet pipe to a storm sewer, which takes the

water away to a natural water channel.

29.Describe the intercepting drains, pipe drains, inlets, catch basins and manholes forsurface drainage.

Solution

Intercepting Drains

Intercepting drains are used on natural slopes to prevent erosion of the cut slops in the

hilly areas. They are sometimes also used to relieve the side ditches of greater discharge than

the one for which they are designed. The water from the intercepting drain is carried down to

the side ditch at specified points along spillways.

Pipe Drains

Pipe drains or storm sewers are widely used for removing surface water and are

sometimes desirable for carrying the water along roadways when sufficient widths of right-

of-way are not available for suitable ditch construction. Vitrified clay sewer pipes and

concrete sewer pipes are the most suitable. Sewers properly designed and constructed in brick

masonry are also used for the purpose. In soils where settlement may occur, corrugated metal

pipe is used. All sections of corrugated metal pipe are connected with metallic bands.

Inlets, Catch Basins and Manholes

Inlets are the openings from gutters or ditches into pipe drains or culverts and are of

various types. Along a rural highway, it may simply be a V-shape or straight concrete

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headwall with or without a paved approach. Drop inlets are used where the water has to be

discharged into a drain or a culvert at a lower level.

Catch basins and manholes are usually of circular shape and are generally connected

to the drop inlets of pipe drains. They are spaced 500 to 1000 feet apart depending upon the

individual design requirement and are meant for inspection.

30. Draw the guardrails and median barriers for roadside design.

Solution

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BY

WYTU

[email protected]

01-685277/685266

09-5006311

C 1 Highway Design

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