Highway Engineering notes by jaspal singh sir.pdf

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TRANSPORTATION ENGINEERING
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CHAPTER- 1 INTRODUCTION
• The process of conveyance from one point to another is termed as
“TRANSPORTATION”.
• Transportation has following effects over the socio- economic aspects of the life:
1. It helps in progress and advancement of the community.
2. Efficient transportation is essential for the economic prosperity and development
of the country.
3. It helps in movement in emergency for defense of the country and to maintain
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MEDIUM OF TRANSPORTATION
Transportation can be achieved by any of the following mediums:
MAJOR MEDIUM
• Land
• Water
• Air
MINOR MEDIUM
• Pipeline
• Conveyor belt
• Elevator
• Cable cars
• Ropeway
• Hyper loop
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On the basis of the above media of transportation, following four major modes of
transportation are used:
1. Roadway/ Highway for road transportation
2. Railway for rail transportation
3. Waterway for water transportation
4. Airways for air transportation
RAILWAYS
• It is the movement of multiple wagons or a train of wagons with steel wheels over
two parallel steel rails, that offer comparatively lesser resistance.
• Hence, the cost of transportation by this method is approximately one- sixth of
that by road transportation, but less flexible.
• Railways are considered as arteries of entire transportation system.
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WATER TRANSPORTATION
• It offers minimum resistance to traction, hence it is the cheapest method amongst the
all.
• But, the time required in this case is comparatively more.
• It is suitable for transportation of bulk goods of relatively low value.
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AIR TRANSPORTATION
• It is the fastest method available for transportation.
• But, the cost involved in this method is also very high.
• It is suitable for transportation of high value goods for large distance.
• This method is affected by weather conditions.
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ROADWAY/ HIGHWAY
• It is the most flexible mode of transportation amongst the all.
• But, it consumes petroleum product at highest rate and rate of emission of
pollution is highest.
• Major road transportation is achieved by highways and expressways.
• Highways are special type of roads designed to allow high speed of vehicle.
• It is generally constructed on embankment as:
1. Better drainage facility
2. Safety in flood time
3. No lateral entry of public or animals
Eg- National Highways (NH) and State Highways (SH)
• Expressways are superior type of highways which are designed as a direct source
of connectivity between two defined points.
• It is also known as “freeway”. It organizes the traffic in channelized way.
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DEVELOPMENT OF ROADS
Development of roads took place in following sequential order:
ROMAN
ROADS
TRESAGUET
ROADS
TELFORD
ROADS
MACADAM
ROADS
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ROMAN ROADS
• These were the earliest of the roads developed for their military purposes.
• The important features of these roads are:
(i) They were built straight, regardless of gradient.
(ii) The soft soil was excavated and removed upto an extent hard strata was
reached.
(iii) The total thickness of construction was in the range of (0.75-1.2)m.
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DRAWBACKS
(i) No cross- slope is provided.
(ii) No drainage system.
(iii) Large foundation stones were provided at bottom, which are of no use, as
pressure due to surface load decreases with depth. Hence, they only increases
the cost.
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TRESAGUET ROADS (FRANCE)
• The main feature of these roads was reduction in overall thickness of the road,
upto 30cm.
• In this case, due consideration was given to the moisture condition and drainage of
the road.
• The subgrade was prepared and a large layer of foundation stone were laid on
edges, which act as a curb stone.
• The space between the kerb is then filled with smaller stones, sizes of which are
reduced as we approach towards top.
NOTE: Metcalf road were developed in England in parallel to previous one but no
recorded literature is available for it.
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TELFORD ROADS
• In these roads also, heavy/ large foundation stones were provided above the soil
subgrade and cross- slope at top surface was given to ensure removal of the water.
• A level subgrade was prepared of width 9m.
• Large foundation stones of thickness (17-22) cm was laid over the subgrade, with
larger stone at the centre and smaller at the edges to provide 1: 45 slope.
• The central portion of about 5.5cm width was filled with two layers of angular
broken stones.
• A 4cm thick gravel surfacing was laid at top and cross- drains were provided at
spacing of 90cm.
• Instead of kerbs, a layer of broken stones were used to impart lateral stability.
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NOTE: From Roman roads to Telford roads, two design considerations were
common:
1. Subgrade soil was constructed on a level surface.
2. Large foundation stones were used to make bottom- most layer.
3. The major change in designing of roads was introduced by Macadam.
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MACADAM ROADS
• Macadam roads differ from previous design in following aspects:
1. Soil subgrade was also laid at a cross- slope of 1 in 36 to avoid the seepage of
water in it.
2. He was the first one to suggest that large foundation stones are not required
to be placed at the bottom layer.
3. Similarly the next layer of pavement was also constructed above this layer with
broken stones of smaller size.
4. Though the total thickness of construction was less, but load distribution was
comparatively better.
5. The size of broken stones at top was decided on the basis of stability under
animal- drawn vehicle.
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NOTE: Different types of specifications were developed for the construction of
bituminous pavement layers for use in base and surface courses.
Some of the specifications used in India are as follows:
(i) WBM (Water Bound Macadam)
(ii) PM (Penetration Macadam)
(iii) BM (Bituminous Macadam)
(iv) DBM (Dense Bituminous Macadam)
(v) WMM (Wet Mix Macadam)
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Q. Which of the following is the chronological sequence in regard to road
construction/ design development?
a) Telford, Tresaguet, C.B.R., Macadam
b) Tresaguet, Telford, Macadam, C.B.R.
c) Macadam, C.B.R., Tresaguet, Telford
d) Tresaguet, Macadam, Telford, C.B.R
[IES: 1998]
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DEVELOPMENT OF ROADS IN INDIA
• Government of India passed the resolution in 1927 for appointment of a
Committee to examine the situation and development of roads in India under the
leadership of M.R. Jayakar.
• Major recommendations of this committee were as follows:
1. The road development in the country should be the subject of “National
Interest”.
2. An extra tax should be leaved on petrol from the users for the development of
roads and would be termed as “Central Road Fund”.
Mohen-
jo- daro
Ashoka Mughal Britishers
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3. A semi- official technical body should be formed to give technical know- how
for development of roads.
4. A research organization should be instituted to carry out research and develop
new techniques of road development.
• As per the recommendation of Jayakar Committee, CRF (Central Road Fund)
was established in 1929.
• After the approval of government, a semi- official technical body was formed in
1934, termed as IRC (Indian Road Congress).
• In 1939, Motor Vehicle Act was brought in place to frame the laws and
ordinances relating to traffic. It governs driver vehicle and owner operation.
• A conference of Chief Engineer of all states was called by IRC for collective
development of roads in India in 1943 (1st 20 year plan) [1943- 1963] (it was
completed in 1961 only) termed as “Nagpur Road Conference”. In this, target of
16km/ 100km2 area of country for development of roads was to be achieved.
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• In 1950, Central Road Research Institute (CRRI) was established for carrying
out research of road technology.
• In 1956, National Highway Act was passed for following purposes:
(i) To declare certain selected highways as NH
(ii) To enter into any land for carrying out survey
(iii) To acquire land and take possession for development of highway
• Due to the early completion of first 20 year plan in 1961, second 20 year plan was
initiated in 1961 (1961- 1981) in Bombay for development of 32km/ 100km2 of
area.
• In 1973, HRB (Highway Research Board) of IRC was setup to give direction
and guidance for research activities in India.
• In 1978, National Transport Policy Committee (NTPC) was appointed to
prepare a comprehensive national transport policy for the country for next 10
years.
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• In 1981, third 20 year road development plan was introduced (1981- 2001) in
Lucknow to develop 82km/ 100km2 of area.
• In 1988, NHAI act was passed.
• In 2000, PMGSY was launched by Indian government .
• Fourth 20 year road development plan should have been introduced in 2001, but
on the insistence of Government, IRC prepared a Road development vision 2021
and 2025.
JAYAKAR COMMITTEE (1927)
CENTRAL ROAD FUND (1929)
INDIAN ROAD CONGRESS (1934)
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MOTOR VEHICLE ACT (1939)
NAGPUR ROAD CONFERENCE (1943)
NAGPUR ROAD PLAN (1943- 1963)
CENTRAL ROAD RESEARCH INSTITUTE (CRRI) (1950)
NATIONAL HIGHWAY ACT (1956) (PROPOSED)
SECOND 20- YEAR ROAD PLAN (BOMBAY ROAD PLAN)
(1961- 1981)
HIGHWAY RESEARCH BOARD (1973)
NATIONAL TRANSPORT POLICY COMMITTEE (NTPC)
(1978)
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THIRD 20- YEAR ROAD PLAN (LUCKNOW
ROAD PLAN) (1981- 2001)
NHAI ACT PASSED (1988)
PMGSY (PRADHAN MANTRI GRAM
SADAK YOJANA) (2001)
ROAD DEVELOPMENT PLAN VISION
2021 AND 2025
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Q. Pradhan Mantri Gram Sadak Yojana (PMGSY), launched in the year 2000, aims
to provide rural connectivity with all- weather roads. It is proposed to connect the
habitations in plain areas of population more than 500 persons by the year
a) 2005
b) 2007.
c) 2010
d) 2012
[GATE: 2005]
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Q. All the specifications for highway planning and design are given by:
a) IRC.
b) HRB
c) MVA
d) CRRI
[SSC: 2018]
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Q. The Road Development Plan for India for the period of 1981 to 2001 is also
known as:
a) Lucknow plan.
b) Nagpur plan
c) Bombay plan
d) Kanpur plan
[SSC: 2018]
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COMPARISON BETWEEN VARIOUS 20 YEAR ROAD
DEVELOPMENT PLANS
1st 20 YEAR PLAN 2nd 20 YEAR PLAN 3rd 20 YEAR PLAN
NAME Nagpur Bombay Lucknow
DURATION 1943- 1963
(completed in 1961)
1961- 1981 1981- 2001
ROAD DENSITY 16 km/ 100 km2 32 km/ 100 km2 82 km/ 100 km2
ROAD PATTERN Star and grid - -
EXPRESS HIGHWAY - 1600 km 20,000 km
CLASSIFICATION OF
ROADS
NH, SH, MDR, ODR
and VR
NH, SH, MDR, ODR
and VR
1. Primary roads: EH and NH
2. Secondary roads: SH and
MDR
3. Tertiary/ rural roads: VR,
ODR
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Q. Nagpur road plan is based on
a) Block pattern
b) Star and grid pattern.
c) Star and circular pattern
d) Hexagonal pattern
[GATE: 1994]
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LENGTH OF THE ROAD AS PER 3rd 20 YEAR ROAD
PLAN
1. Total length of road = max (i) 4.74 × number of towns and villages
(ii) Road density × area
2. Length of NH =
Area (km2)
50
3. Length of SH = max (i)
Area (km2)
25
(ii) 62.5 × number of towns and villages – length of NH
4. Length of MDH = max (i)
Area (km2)
12.5
(ii) 90 × number of towns and villages
5. Length of ODR and VR = Total – (ii) – (iii) – (iv)
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Q. The length of National Highways as per 3rd 20 year (Lucknow) road plan is given
by:
a) Area of the country/ 75
b) Area of the country/ 50.
c) Area of the country/ 40
d) Area of the country/ 25
[IES: 2000]
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HIGHWAY PLANNING
• Highway planning is of great importance when the funds available are limited,
whereas the total requirement is much higher.
• The objective of highway planning are as follows:
1. To plan the overall network of road efficiently in minimum cost.
2. To divide the overall plan in phases to decide the priorities.
3. To plan for future requirement and improvement of the roads.
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CLASSIFICATION OF ROADS
Roads are classified as follows:
A. On the basis of duration of their use:
(i) All weather roads: paved and non- paved roads
(ii) Fair weather roads: surface and non- surface roads
B. On the basis of traffic volume
C. On the basis of load transported/ tonnage
D. On the basis of location and function
1. National Highway (NH): These are main highway running through length and width of
country, connecting major ports, foreign highway, capitals of large states and large
industrial area, tourist and places of strategic importance (defense).
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2. State Highway (SH): These are arterial roads of states, connecting the national
highways of adjacent state, district headquarters and important cities.
3. Major District Roads (MDR): They are important roads within a district,
serving area of production, markets, etc.
4. Other District Roads (ODR): These are roads serving rural areas of production
and providing them outlet to the market.
5. Village Roads (VR): These are roads connecting villages.
NOTE: Urban roads are also classified as follows:
1. Arterial roads
2. Sub- arterial roads
3. Collector streets
4. Local streets
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TYPES OF ROAD PATTERN
• The various types of road pattern may be classified as follows:
1. RECTANGULAR/ BLOCK PATTERN
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2. HEXAGONAL PATTERN
3. RADIAL OR STAR AND BLOCK PATTERN
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4. RADIAL OR STAR AND CIRCULAR
5. RADIAL OR STAR AND GRID
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MAXIMUM STAURATION SYSTEM/ UTILITY
FACTOR
• This system is used to choose the best alignment amongst the various options
available.
• It depends upon population and production.
RULES TO DECIDE THE FACTOR
1. Provide utility factor (UF) of 0.5 to the lowest population and increase it by
multiplying with 2 for next range of population. For eg- 0.5, 1, 2, 4, 8, 16….
2. Provide UF of ‘1’ to the agricultural production.
3. Provide UF to industrial production as per the weightage.
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ENGINEERING SURVEY FOR HIGHWAY
ALIGNMENT
• In order to decide or finalize the probable alignment, following surveys are being
carried out:
1. MAP STUDY: Various alignments are drawn on map passing through minimum
number of obstructions and maximum utilization area.
2. RECONNAISANCE: It is done by visiting the location under consideration to
identify the features which are not available on map or which are changed over
the period of time. Feasibility is also checked for the possible alignment in this
stage.
3. PRELIMINARY SURVEY: In this survey, chain, compass, levelling, soil
investigation, drainage provision, traffic studies are carried out and maximum
utilization area is decided.
4. DETAILED SURVEY: In this, planning, designing, material estimation and
cost estimation, etc. are done and a DPR is prepared.
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Q. Under the Nagpur Road Plan, which of the following are NOT relevant in
planning the road development programme in a backward district?
1. Existing agriculture drainage network of drain canals
2. Existing number of Panchayat unions
3. Existing number of villages mud- track roads
4. Number of villages with population of 10000 and above
a) 1, 2, 3 and 4.
b) 1, 2 and 3 only
c) 1, 2 and 4 only
d) 2, 3 and 4 only
[IES: 2013]
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Q. In which of the following location surveys of the road soil profile, is sampling
done upto a depth of 1m to 3m below the existing ground level?
a) Preliminary survey.
b) Final location survey
c) Construction survey
d) Material location survey
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Q. Preliminary project report for a road project must contain
a) The detailed estimated cost based on detailed design
b) The several alternative of the project that have been considered
c) The soil survey, traffic survey, concept design and approximate cost.
d) The contract documents for inviting tenders
[IES: 1999]
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CHAPTER- 2 GEOMETRIC DESIGN
Geometric design of a highway deals with all the dimensions and layout of visible
features of highway, such that it provides maximum efficiency at minimum cost and
reasonable safety.
Geometric design of highway deals with:
1. Cross- sectional elements
2. Sight distance considerations
3. Horizontal alignment details
4. Vertical alignment details
5. Intersection details
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For designing of highway elements, following factors are considered:
I. DESIGN SPEED
• Design speed of vehicle depends upon type of road over which it ply (moves), for
eg – NH, SH, etc.
• Design speed of vehicle decides the cross- sectional elements like- width,
clearance, sight distance, radius of curve, superelevation, transition, gradient,
length of summit, valley, etc.
II. TOPOGRAPHY
• Topography or terrain condition influences the design speed, that in turn governs
the designing of the highway element as above.
• For eg – in plain terrain, on SH, Vper = 100 kmph whereas the same speed on
rolling terrain is, Vper = 80 kmph and on mountaneous terrain, Vper = 50 kmph.
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III. TRAFFIC FACTORS
• Traffic factors includes vehicle characteristics and human characteristics.
• In order to design highway, standard size of vehicle is considered (car) in case of
mixed traffic operation.
• Human traffic includes physical, mental and psychological characteristics of
driver and pedestrians.
IV. DESIGN HOURLY VOLUME AND CAPACITY
• The traffic volume fluctuates over the period of time, hence, the designing must be
done for peak hours, but it will be highly uneconomical to do so, hence designing
is being done for reasonable value of traffic volume, termed as “Design Hourly
Volume”.
V. ENVIRONMENTAL FACTORS
Factors like aesthetics, air pollution, noise pollution, landscaping also governs the
designing of highway elements.
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HIGHWAY ELEMENTS
I. HIGHWAY CROSS- SECTION ELEMENTS
1. PAVEMENT SURFACE CHARACTERISTICS
• It depends upon pavement type, which in turn depends on availability of material,
cost, composition of traffic, climatic conditions, method of construction, etc.
• Pavement surface characteristics include:
(i) Friction
(ii) Unevenness
(iii) Reflection properties
(iv) Drainage of surface water
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FRICTION/ SKID RESISTANCE
• It decides the operating speed and minimum distance required for stopping the
vehicle.
• It is further classifies into two:
1. Longitudinal friction
2. Lateral or transverse friction
• Maximum friction is developed when brakes are applied upto complete extent.
• Friction also governs rotational and translational movement of the vehicle.
• For uniform condition, Rotation = Translation
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NOTE: (i) When the path travelled along the road surface is more than the
circumferential movement of wheels due to their rotation, it is termed as “Skid”.
Translational motion > Rotational motion
For pure skid, Rotational motion = 0
For eg- When brakes are applied, rotation stops but skidding occurs
(ii) When the circumferential movement of wheels is more than the path travelled
along the road surface, it is termed as “Slip”.
Rotational motion > Translational motion
For pure slip, translational motion = 0
For eg- When wheels of vehicle are in mud, it rotates but do not move ahead.
Condition Rotation Translation Impact
If longitudinal friction is
more
No Yes Tyre burn
If longitudinal friction is less Yes No No movement of vehicle (fuel burn)
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Friction depend upon following factors:
1. Type of pavement surface (bitumen, concrete, earthwork)
2. Roughness of pavement (texture)
3. Condition of surface (dry or wet, rough or smooth)
4. Condition of tyre (new or old)
5. Speed of vehicle (high speed: less friction, low speed: more friction)
6. Extent of brake application (full or partial)
7. Temperature of tyre and pavement
NOTE: New tyre is more dependable in adverse conditions
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• For the calculation of stopping sight distance, the longitudinal friction co-
efficient is taken to be (0.35- 0.40).
• At f = 0.40, the retardation available is approximately 4m/s2.
• Lateral friction is taken as 0.15.
UNEVENESS
• Presence of undulations on the pavement surface is called unevenness.
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• This unevenness results in:
1. Increased fatigue
2. Reduces speed
3. Increases fuel consumption
4. Increases wear and tear of vehicles
5. Increases chances of accidents
• The unevenness of pavement is measured with the help of equipment called
“Bump Indicator” (BI) in terms of unevenness index, which is the vertical
undulations of pavement surface recorded per unit length of road (in India,
mm/km is used).
• The different values of unevenness index and the corresponding serviceability of
road is as follows: Unevenness index (mm/ km) Type of road
< 1500 Good
1500 - 2500 Satisfactory
2500 - 3500 Bad
> 3500 Uncomfortable
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BUMP INDICATOR
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NOTE: 1. Internationally, the riding quality of pavement surface is quantified in
terms of roughness and is expressed as “International Roughness Index”.
2. It can also be related with unevenness index as follows:
BI (mm/km) = (IRI)1.12 (m/km)
Unevenness of the pavement depends on following factors
1. Improper compaction
2. Use of improper compaction methods
3. Use of inferior quality materials
4. Improper surface and sub- surface drainage
5. Poor maintenance of pavement surface
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Q. ASSERTION (A): IRC has recommended a minimum coefficient of friction in
the longitudinal direction on wet pavements after allowing a suitable factor of safety
in the range 0.15 – 0.30.
REASON (R): When the longitudinal coefficient of friction of 0.40 is allowed for
stopping the vehicle, the resultant retardation is 3.93 m/s2, which is not too
uncomfortable to the passengers.
a) Both A and R are true and R is correct explanation of A
b) Both A and R are true and R is not a correct explanation of A
c) A is true but R is false
d) A is false but R is true.
[IES: 2011]
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Q. ASSERTION (A): Worn out (smooth) tyres offer higher friction factors on dry
pavements than new tyres with treads well intact.
REASON (R): Reduced pneumatic pressure is held in tubes which carry smooth
tyres over them
b) Both A and R are true and R is not a correct explanation of A.
d) A is false but R is true
[IES: 2010]
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Q. The value of lateral friction or side friction used in the design of horizontal curve
as per Indian Roads Congress guidelines is
a) 0.40
b) 0.35
c) 0.24
d) 0.15.
[GATE: 2009]
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Q. The longitudinal coefficient of friction on highway for calculation of stopping
distance in geometrical design is:
a) 0.3 to 0.34
b) 0.5
c) 0.25 to 0.29
d) 0.35 to 0.4.
[SSC: 2018]
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Q. Which instrument is used for the measurement of the longitudinal coefficient of
friction?
a) Bump integrator
b) Both bump integrator and roughometer.
c) Roughometer
d) Speedometer
[SSC: 2017]
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REFLECTIVE PROPERTIES
• Visibility over the pavement surface depends upon its color and light
characteristics, the glare caused by the reflection of head light is high on wet
pavement surface than dry pavement surface.
• Light colored pavement gives good visibility at night but produces more glare
during sunlight. On the other hand, dark color pavement offers good visibility at
day and poor at night.
2. CROSS- SLOPE/ CAMBER
• It is the slope provided to the road surface in the transverse direction to drain the
rain water from the road surface to avoid the following:
1. Stripping of bitumen from the aggregates in the presence of water.
2. Swelling and heaving of subgrade, in case water seeps into it.
3. To avoid the slipping of vehicle over the wet pavement.
4. To avoid the glare in wet pavement.
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• On straight roads, it is provided by raising the centre of the carriageway w.r.t. the
edges forming the crown on the highest point along the centre line.
• On horizontal curve, with superelevation, the drainage is provided by lifting the
outer edge.
STRAIGHT ROADS HORIZONTAL CURVE
• It is represented by any of the following ways:
1. As % : for eg- cross- slope = 5%; tan𝜃 = 5/100
2. As fraction: for eg- cross- slope = 1 in 20 or 1/20 or 0.05; tan𝜃 = 1/20
1 in 20 means, 1V: 20H
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• The value of cross- slope depends upon following factors:
1. Type of pavement surface
2. Amount of rainfall
• Cross- slope provided would be comparatively increased if amount of rainfall is
more and pavement surface is permeable.
• The cross- slope of shoulder should be more than that of pavement, so as to avoid
accumulation of water at junction of the two.
Type of road surface Range of cross- slope
Heavy rainfall Light rainfall
Cement concrete and high type bituminous surface 2% 1.7%
Thin bituminous surface 2.5% 2%
WBM and gravel pavement 3% 2.5%
Earthern road 4% 3%
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• Cross- slope of shoulder should be 0.5% more than cross- slope of adjoining
pavement, having minimum value of 3% and maximum value of 5%.
5% ≮ CSshoulder = (0.5% + CSpavement) ≮ 3%
• The cross- slope on expressways for carriageway and paved shoulder and edge
strip with bituminous surface is 2.5% with rainfall exceeding 1000mm and 2% for
places having rainfall less than 1000mm.
• If too steep cross- slope is provided, then:
1. Toppling of slow moving and over- loaded vehicles.
2. Tendency of most vehicles to travel along the centre line.
3. Uncomfortable side thrust and drag on the vehicle.
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TYPES OF CROSS- SLOPE
Cross- slopes are of following types:
1. Straight line Camber:
1
n
=
H
Τ
w
2
𝐇 =
𝐰
𝟐𝐧
2. Parabolic Camber:
𝐲 =
𝟐𝒙𝟐
𝐧𝐰
3. Composite Camber:
Parabolic at top and straight at sides.
NOTE: For CC pavement, straight line camber is preferred as it is easier to lay.
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3. WIDTH OF PAVEMENT/ CARRIAGEWAY
• Width of pavement depends upon width of traffic lane and number of lanes.
• The portion of carriageway width that is intended for one line of traffic movement
is termed as “traffic lane”.
• Width of traffic lane is decided on the basis of type of vehicle moving it along
with some clearance in both the sides.
• Passenger car is considered as standard vehicle to decide the width of
carriageway.
NOTE: Width of passenger car = 2.44 ≈ 2.5m
• For rural highway, if pavement has two or more lanes (multi- lanes), width of
single lane = 3.5m.
• The number of lanes to be provided depends upon traffic volume.
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The width of the carriageway for different conditions are as follows:
Type of road Width of carriageway
1. Single lane road 3.75 m
2. Two lane road without raised kerbs 7 m
3. Two lane road with raised kerbs 7.5 m
4. Intermediate carriageway 5.5 m
5. multi- lane pavement 3.5 m per lane
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4. MEDIANS/ TRAFFIC SEPARATOR
• In highway with divided carriageway or pavement, a median is provided between
two sets of traffic lanes intended to divide the traffic moving in opposite
directions.
• The main function of median is to prevent head- on collision between vehicles
moving in opposite direction.
• It also serves following other functions:
1. To channelize traffic into streams.
2. To protect the pedestrians.
3. It can be used to reduce the glare of the head light of opposite moving vehicle by
providing green cover on it.
4. To segregate the slow traffic.
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• Medians can be provided in following forms:
1. As pavement marking
2. As physical divider (mechanical separator)
• Desirable width of median is (8-14)m.
• It includes the provision for future expansion of roads.
• In order to reduce the glare of headlight of opposite vehicle, a minimum of 6m
width is required.
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• IRC recommends minimum width of 5m for median, that can be reduced to 3m
where land is restricted.
• On bridges, width required for median is in the range of (1.2- 1.5)m.
• The median should be normally of uniform width throughout the length of the
pavement or carriageway, but where its width is changed a transition of 1 in 15 to
1 in 20 must be provided.
• In urban areas, minimum width of median to be provided is 1.2m and desirable
width is 1.5m
• For expressways, minimum width to be provided is 12m and desirable width is
15.5m.
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5. KERB
• Kerb indicates the boundary between the pavement and median or foot path or
island or shoulder.
• Kerbs are mainly divided in following three categories:
A. Low kerb: It is of height 100mm (10cm) above the pavement surface (edge)
with a slope to enable the vehicle to climb the kerb at slow speed.
• It is also termed as “Mountable Kerb” which encourages the traffic to remain in
the through traffic lanes yet allows the driver to enter the shoulder area at slow
speed.
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B. Semi- barrier type kerb: It is provided on the periphery of the roadway where
the pedestrian traffic is high. This type of kerb is of height of about 150mm above
the pavement edge with slope of 1:1 on top 75mm.
• This kerb prevents encroachment by parking vehicles, but in case of emergency, it
is possible to drive over this kerb with difficulty.
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C. Barrier type kerb: It is provided in built- up areas adjacent to footpaths with
considerable pedestrian traffic. Height is 20cm (200mm) above the pavement edge
of step slope of 1V: 0.25H.
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6. SHOULDER
• Shoulders are provided on both sides of the pavement, all along the road in the
case of undivided carriageway and on outer edge of divided carriageways.
• The earthern shoulder should have sufficient strength to carry the vehicular load in
case of emergency.
• The minimum shoulder width as per IRC is 2.5m.
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FUNCTIONS OF SHOULDER
Shoulder serves the following functions:
1. It imparts structural stability to the pavement.
2. It increases the capacity and operating speed of pavement.
3. In emergency, it can be sued as mode of movement.
4. It can also act as a service lane for the vehicles that are disabled.
5. The surface of the shoulder may be rougher than the traffic lanes, so as to
discourage the vehicle to fly over it.
6. The color of the shoulder should be different from that of pavement, so as to
differentiate between the two.
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7. ROAD MARGINS
The various elements included in the road margins are guard rails, foot path, drive
way, cycle track, parking lane, lay- bays, front edge, road and embankment slope.
(i) Guard rail: These are provided at the edge of the shoulder when the road is
constructed running of the embankment, especially when the height of fill is
more than 3m.
(ii) Foot path/ Side walk: In order to provide safe facility to the pedestrian to walk
along the roadway, footpath/ side walk is provided in urban areas, where the
pedestrian traffic is comparatively more.
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• Its minimum width required is 1.5m and desirable width is 2m.
• It is provided with cross- slope of 2.5 – 3% and has comparatively smoother
surface than pavement.
(iii) Drive ways: It connects the highway with local commercial establishment like
service station, fuel station, restaurant, etc.
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(iv) Cycle track: These are provided in urban areas for the safe movement of cycle
traffic.
• The minimum width required is 2m for cycle track and it can be increased by 1m
for each additional cycle way.
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(v) Parking lanes: These are provided on urban roads to allow kerb parking.
• As far as possible, only parallel parking should be allowed as it is safer for moving
vehicles and space required would also be less.
• For parallel parking, the minimum width is 3m.
(vi) Bus bays: It may be provided by pushing back the kerb to avoid the conflict
with the moving traffic and must be located atleast 75m away from intersection.
• It is used for safe loading and unloading of passengers.
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(vii) Lay byes: These are provided near public convenience to avoid the conflict with
running traffic. Minimum width is 3m.
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(viii) Frontage roads: These are provided to give access to the property along the
highway to control the access to the expressway.
(ix) Embankment slope: If pavement is constructed over embankment, slopes are
also provided along it, of magnitude 1:3.
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NOTE: 1. ROADWAY/ WIDTH OF FORMATION
It is the sum of width of pavement or carriageway including separator and the
shoulder. Roadway width is the top width of highway embankment or bottom width
of highway cutting excluding the side ways.
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Width of roadway of various class of roads are as follows:
Type of roads Roadway width (m)
Plain and rolling terrain Mountaineous and steep terrain
NH and SH
(a) Single lane
(b) Two lane
12
12
6.25
8.8
MDR
(a) Single lane
(b) Two lane
9
9
4.75
-
ODR
(a) Single lane
(b) Two lane
7.5
9
4.75
-
Village roads 7.5 4
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NOTE: 2. ROADLAND/ LAND WIDTH/ RIGHT OF WAY
• It is the area of the road, along its alignment keeping in view its future expansion
also.
• Construction of a particular type of building is only permitted with sufficient
setback from the road boundary upto control line.
• Width of land for different roads in rural areas are as follows:
Road Classification Plain and Rolling Mountaneous
Open Built area Open Built area
Expressway 90m - 60m -
NH and SH 45m 30m 24m 20m
MDR 25m 20m 18m 15m
ODR 15m 15m 15m 12m
VR 12m 10m 9m 9m
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Q. ASSERTION (A): Road camber helps in surface drainage.
REASON (R): In a curved road alignment, superelevation serves the purpose of
camber.
b) Both A and R are true and R is not a correct explanation of A.
d) A is false but R is true
[IES: 2008]
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Q. Width of carriageway for a single lane is recommended to be
a) 7.5m
b) 7.0m
c) 3.75m.
d) 5.5m
[GATE: 2000]
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Q. Cross- slope given to the pavement for safe drainage of water is:
a) Cant
b) Kerb
c) Shoulder
d) Camber.
[SSC: 2018]
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Q. The camber for hill roads in case of bituminous surface is adopted as:
a) 2.0%
b) 2.5%.
c) 3.0%
d) 3.5%
[SSC: 2011]
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Q. A portion of the roadway contiguous with the travelled way and is intended for
accommodation of stopped vehicle is called as:
a) Carriageway width
b) Curbs
c) Shoulder.
d) Median
[SSC: 2018]
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Q. Right of way is the summation of the width of
a) Carriageway and shoulder
b) Carriage way, shoulder and road margins.
c) Carriage way and road margins
d) Road margins and shoulder
[SSC: 2017]
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Q. Which of the following is correct statement for the cross- slope of the shoulder?
a) It is 1% flatter than the cross- slope of pavement
b) Its minimum value is 2%
c) It is 0.5% steeper than the cross- slope of the pavement.
d) Its value is equal to the cross- slope of pavement
[SSC: 2017]
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Q. The cross section for a highway is taken at
a) Right angle to the centre line
b) 30m apart
c) Intermediate points having abrupt change in gradient
d) All options are correct.
[SSC: 2016]
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Q. Pick up the incorrect statement from the following:
The width of the right of way is decided to accommodate
a) Formation width
b) Side slopes
c) Horizontal curve
d) Vertical curve.
[SSC: 2016]
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SIGHT DISTANCE
• Sight distance is the length of the road visible ahead to the driver at any instance.
It is considered by taking the height of the eye of driver to be 1.2m and height of
object as 0.15m.
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• Restriction to the visibility or sight distance will be caused in following cases:
1. At horizontal curve: When line of sight is obstructed by object at the inner side
of the curve.
2. At vertical curve: The LOS is obstructed by the road surface of the curve.
3. At an uncontrolled intersection: When a driver from one of the approach road is
able to sight a vehicle from another approach road towards it.
NOTE: When obstruction is not there, more sight distance is available.
• The sight distance available to the driver is dependent upon following factors:
1. Features of road, for eg- horizontal curve, traffic conditions, position of
obstruction, etc.
2. Height of driver’s eye above road surface
3. Height of object above road surface
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TYPES OF SIGHT DISTANCE
STOPPING SIGHT DISTANCE
SAFE OVERTAKING DISTANCE
SAFE SIGHT DISTANCE (for entering into uncontrolled intersection)
INTERMEDIATE SIGHT DISTANCE
HEADLIGHT SIGHT DISTANCE
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STOPPING SIGHT DISTANCE
• The minimum distance visible to a driver ahead to safely stop a vehicle travelling
at design speed without collision is termed as “Stopping Sight Distance” (SSD).
• It is also termed as “Absolute Minimum Sight Distance” or “Non- Passing
Sight Distance”.
• Factors governing stopping sight distance are:
A. TOTAL REACTION TIME OF DRIVER:
• It is the time taken from the instant the object is visible to the driver to the instant
brakes are applied effectively.
• This total reaction time is further divided into different components and can be
explained as follows:
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A. PERCEPTION TIME (P)
• It is the time required for the sensation received by the eyes or ears of the driver to
be transmitted by the brain through the nervous system and spinal cord.
B. INTELLECTION TIME (I)
• It is the time required by the driver to understand the situation. It is also the time
required for comparing different thoughts, re- grouping and registering new
sensations.
C. EMOTION TIME (E)
• It is the time elapsed during emotional sensations and other mental disturbances,
fear, anger, superstition, etc, with reference to the situation to come into play. This
time varies from person to person and even for same person in different situations.
D. VOLITION TIME (V)
• It is the time taken by the driver for final action, like application of brakes.
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• The above can be termed as “PIEV” analysis for total reaction time.
tR = (P+I+E+V) time
tR, min = Reflex action time
NOTE: 1. It is also possible that the driver may apply the brake or take any other
avoiding action, like turning by the reflex action, without normal thinking process,
that is observed to be minimum time for avoiding the collision.
2. This reaction time depends upon several factors, like driver’s skill, type of
obstruction involved, environmental conditions, age, mental health, etc.
B. DESIGN SPEED:
• During the total reaction time of the driver, the distance moved by the vehicle
depends upon design speed.
• Braking distance, i.e. distance travelled by vehicle before coming to stop/ halt alos
depends on design speed.
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C. BRAKING EFFICIENCY:
• It is defined as the % of force developed by application of brakes in relation to
maximum friction available between tyre and road.
𝛈𝐁 =
𝐟
𝐟𝐦𝐚𝐱
× 𝟏𝟎𝟎 =
𝐅𝐨𝐫𝐜𝐞 𝐝𝐞𝐯𝐞𝐥𝐨𝐩𝐞𝐝
𝐌𝐚𝐱𝐢𝐦𝐮𝐦 𝐟𝐨𝐫𝐜𝐞 𝐚𝐯𝐚𝐢𝐥𝐚𝐛𝐥𝐞
If ηB = 100%, skid will occur on application of brakes; which is difficult to control.
Hence, braking force should not exceed the friction force between wheels and tyres.
D. FRICTIONAL RESISTANCE BETWEEN ROAD AND TYRE:
• The frictional resistance developed between the road and tyre depends upon co-
efficient of friction. Higher is coefficient of friction, higher is the frictional
resistance and lower is SSD.
• Co- efficient of friction further depends upon condition of tyre and roads.
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• It is often linked with the design speed of vehicle as follows:
E. GRADIENT:
• Gradient of the road, either in assistance or resistance of the vehicle, depends upon
type of gradient (up or down), thereby either increases or decreases SSD.
Speed (kmph) 20 – 30 40 50 60 70 80 ≥ 100
Longitudinal friction 0.4 0.38 0.37 0.36 0.36 0.35 0.35
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Q. Total reaction time of a driver does not depend upon
a) Perception time
b) Brake reaction time
c) Condition of mind of the driver
d) Speed of vehicle.
[IES: 2000]
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ANALYSIS OF STOPPING SIGHT DISTANCE
SSD = LL + LB
The stopping sight distance of vehicle includes:
• The distance travelled by the vehicle at uniform design speed during the total
reaction time, termed as “Lag distance” (LL).
• Distance travelled by the vehicle after the application of brake, until it stops,
termed as “Braking distance” (LB).
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1. LAG DISTANCE 𝐋𝐋 = 𝐯𝐃 × 𝐭𝐑
Where LL = Lag distance (m)
vD = Design speed (m/s)
tR = Reaction time (s)
𝐋𝐋 = 𝟎. 𝟐𝟕𝟖 × 𝐕𝐃 × 𝐭𝐑
Where, VD = Design speed (kmph)
NOTE: Reaction time, tR = 2-4 sec, but as per IRC, tR – 2.5 sec for SSD.
2. BRAKING DISTANCE
(i) For flat road:
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∆KE = Work done by friction
1
2
mvf
2
−
1
2
mvi
2
= −FLB
𝐋𝐁 =
𝐯𝟐
𝟐𝐠𝐟
(𝐦) where v (m/s); g(m/s2)
𝐋𝐁 =
𝐕𝟐
𝟐𝟓𝟒𝐟
(m) where V (kmph)
(ii) For gradient (ascending and descending):
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∆KE = Work done by friction
0 −
1
2
mv2
= −FLB ∓ WsinθLB
−
1
2
mv2
= −fmgcosθLB ∓ mgsinθLB
When θ is small, θ ≈ sinθ ≈ tanθ = s; cosθ = 1
𝐋𝐁 =
𝐯𝟐
𝟐𝐠(𝐟±𝐬)
where v (m/s)
𝐋𝐁 =
𝐕𝟐
𝟐𝟓𝟒(𝐟±𝐬)
where V (kmph)
+ is used for ascending gradient
- is used for descending gradient
SSD = LL + LB
SSD = 𝟎. 𝟐𝟕𝟖 × 𝐕𝐃 × 𝐭𝐑 +
𝐕𝐃
𝟐
𝟐𝟓𝟒(𝐟±𝐬)
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NOTE: 1. SSD must be available at each and every section of the road.
2. As the SSD required on descending gradient is higher, it is necessary to determine
the critical value of SSD for the descending gradient on the road with gradient and
for two way traffic flow.
3. On the restricted width or on single lane road, when two- way movement of
traffic is permitted, the minimum stopping distance is equal to twice the SSD to
enable both the vehicles coming from opposite sides to stop.
4. If SSD cannot be provided on any stretch of road due to unavoidable reasons, for
the design speed available, the speed should be restricted either by installing speed
limit regulation signs or by forced reduction of speed (by speed breaker).
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• This is however temporary and efforts must be made to provide SSD over the
period of time by changing the alignment or by moving the obstruction.
• IRC recommends the SSD values as follows:
Design speed (kmph) SSD (2m)
20 20
25 25
30 30
40 45
50 60
60 80
65 90
80 120
10020 180
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Q. Consider the following factors:
1. Reaction time
2. Speed
3. Coefficient of longitudinal friction
4. Gradient
Which of these factors are taken into account for computing braking distance?
a) 1 and 3
b) 1, 2 and 4
c) 2, 3 and 4.
d) 2 and 3
[IES: 2002]
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Q. Stopping sight distance depends upon
a) Total reaction time of the driver
b) Speed of the vehicle
c) Efficiency of brakes
d) All of the given options.
[SSC: 2016]
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Q. SSD and friction co- efficients are
a) Directly proportional to each other
b) Unrelated
c) Inversely proportional to each other.
d) Either directly of inversely proportional; they depends upon nature
[GATE: 2002]
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Q. Stopping sight distance is the minimum distance available on a highway which is
the
a) Distance of sufficient length to stop the vehicle without collision.
b) Distance visible to a driver driving night driving
c) Height of the object above the road surface
d) Distance equal to the height of the driver’s eye above the road surface
[GATE: 2000]
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Q. The reaction time for calculating stopping sight distance may be assumed as
a) 5 sec
b) 2.5 sec.
c) 0.5 sec
d) 10 sec
[GATE: 1999]
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Q. The distance travelled by a moving vehicle during perception time and brake
reaction time is known as
a) Sight distance
b) Stopping distance
c) Lag distance.
d) Braking distance
[GATE: 1987]
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OVERTAKING SIGHT DISTANCE
• If all the vehicles ply on a road at the design speed, then there would be no need
for overtaking, but practically this never happens.
• Hence, vehicle moving at design speed needs to overtake slow moving vehicle.
• The minimum distance open to the vision of the driver of a vehicle intending to
overtake slow vehicle with safety against traffic in opposite direction is termed as
“OSD” or “Safe Passing Sight Distance” or “Safe Passing Sight Distance”.
• OSD is measured along centre line of the road, considering eye level of the driver
at 1.2m above the surface, observing the object at height of 1.2m.
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FACTORS AFFECTING OSD
1. Speed of vehicle
a) Overtaking vehicle
b) Overtaken vehicle
c) Vehicle coming from opposite direction
2. Reaction time and skill of the driver
3. Gradient of road
4. Condition of overtaking vehicle, which governs the rate of acceleration
5. Distance between two vehicles (overtaking and overtaken)
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ANALYSIS OF OSD
A = Overtaking vehicle
B = Overtaken vehicle
V = Design speed
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a) d1 = It is the distance travelled by overtaking vehicle “A” during the reaction
time “tr” of the driver, before starting to overtake vehicle “B” at speed of VB.
b) d2 = It is the distance travelled by vehicle “A” during the actual overtaking
operation of time “T”.
c) d3 = It is the distance travelled by on coming vehicle “C” during the actual
overtaking operation of “A” for time “T”.
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ASSUMPTIONS IN ANALYSIS OF OSD
1. Overtaking vehicle is forced to reduce its speed upto the speed of overtaken
vehicle for reaction time.
2. When the driver of vehicle finds sufficient clear gap, decides within the reaction
time to overtake.
3. The vehicle ‘A’ accelerates and overtakes the vehicle ‘B’ within a distance ‘d2’
during the time ‘T’.
4. The distance ‘d2’ can be splitted into three components.
5. During this overtaking time, the vehicle ‘C’ coming from opposite direction
travels through distance ‘d3’.
d1 = vb × tr
d1 = 0.278 Vb × tr (where Vb is in kmph)
NOTE: tr = 2 sec
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d2 = 2s + b
Where s = space headway = minimum spacing between two vehicles which depends
upon the speed of the vehicle
s = (0.7 vb + 6) (where vb is in m/s)
s = (0.2 Vb + 6) (where Vb is in kmph)
B = vb × T = 0.278 Vb × T
d2 = vb × T +
1
2
a T2
d2 = 0.278 Vb × T +
𝟏
𝟐
a T2
2s + b = 0.278 Vb × T +
1
2
a T2
𝐓 =
𝟒𝐬
𝐚
Where, a = acceleration of overtaking vehicle (m/s2)
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NOTE: Overtaking time ‘T’ depends upon its average acceleration and speed of
overtaken vehicle
d3 = vd × T = 0.278 Vd × T
Where, Vd = design speed (kmph)
OSD = d1 + d2 + d3
OSD = (0.278 Vb × tr ) + (0.278 Vb × T +
𝟏
𝟐
a T2) + (0.278 Vd × T)
NOTE: In case the speed of overtaken vehicle is not given, it may be taken as 4.5
m/s or 16 kmph less than design speed.
vb (m/s) = vd (m/s) – 4.5 m/s
Vb (kmph) = Vd (kmph) – 16 kmph
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The acceleration of the overtaking vehicle varies depending upon the several
factors:
1. Type of vehicle
2. Condition of vehicle
3. Load on the vehicle
4. Speed of vehicle
5. Characteristics of driver
Maximum overtaking acceleration at different speeds are as follows:
Speed (kmph) Acceleration (m/s2)
25 1.41
30 1.30
40 1.24
50 1.11
65 0.92
80 0.72
100 0.53
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EFFECT OF GRADIENT ON OSD
• The overtaking sight distance requirement may increase on ascending as well as
descending gradient.
• In descending gradient, acceleration of overtaking vehicle increases, but overtaken
vehicle may also accelerate to a greater distance ‘b’ during the overtaking time.
Thus, we cannot comment as there are two variables.
• In ascending gradient, the acceleration of overtaking vehicle will be less but
overtaken vehicle would also move with lower velocity, hence we cannot
comment on OSD.
• Hence, on mild gradient (as that in plain and rolling terrain), OSD at both
ascending and descending gradient are generally equal to that of level stretch.
• However, for steeper grades, OSD should be greater than minimum OSD at plain
level road.
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OSD on two- lane highway for different speeds are as follows:
Speed (kmph) OSD (m)
40 165
50 275
60 300
65 340
80 470
100 640
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NOTE: . It is desirable that OSD should be available on most of the road stretches.
• On road stretches with two- way traffic:
OSD = d1 + d2 + d3
• On road stretches with one- way traffic
OSD = d1 + d2
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OVERTAKING ZONE
• If OSD cannot be provided over a particular stretch of a road section, in such
cases, for same overtaking of the vehicle at design speed, opportunity must be
given to the vehicle. Such zones are termed as “Overtaking Zones”.
SP1 = Sign post “Overtaking zone ahead”
SP2 = Sign post “End of Overtaking zone”
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NOTE: 1. If at stretches of road, OSD cannot be provided as suggested by IRC, in
such case, sight distance is desirable to be kept as twice of SSD and it is termed as
“Intermediate Sight Distance” (ISD).
ISD = 2× SSD
2. The measurement of ISD can be made assuming both the height of eye of driver
and that of object to be 1.2m.
OSD > ISD > SSD
Distance (m) Reaction time (s) Height (m)
Driver’s eye Object
SSD 2.5 1.2 0.15
OSD 2 1.2 1.2
ISD 2.5 1.2 1.2
Space headway 0.7 - -
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Q. At highway stretches where the required overtaking sight distance cannot be
provided, it is necessary to incorporate in such sections the following:
a) At least twice the stopping sight distance.
b) Half of the required overtaking sight distance
c) One- third of the required overtaking sight distance
d) Three times the stopping sight distance
[GATE: 1998]
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SIGHT DISTANCE AT INTERSECTION
A. UNCONTROLLED INTERSECTION
• On all approaches of intersecting roads, there should be clear view across the
corner from the sufficient distance so as to avoid the collision.
• The design sight distance at intersection may be based on three possible
conditions:
1. Enabling the approaching vehicle to change the speed (slow down).
2. Enabling the approaching vehicle to stop.
3. Enabling stopped vehicle to cross the road.
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1. The sight distance should be sufficient to enable either one or both approaching
vehicle to change the speed to avoid collision.
• The vehicle approaching from the minor must slow down.
• Total reaction time required for the driver to decide to change speed is 2s and
at-least one more second is required for making the change in speed.
Total time = 2 + 1 = 3 sec
Hence, SD = 0.278 Vd × tr = (0.278 Vd × 3 ) m
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2. The distance for the approaching vehicle should be sufficient to bring either both
or one of the vehicle before reaching the conflict. Hence, it will be equal to SSD.
3. In this case, vehicle entering the intersection from the minor roads are controlled
by ‘STOP’ or ‘GIVE WAY’ sign. So, the vehicles have to stop and then proceed
to cross the main road.
• In this case, the total time required by the stopped vehicle would include to start,
accelerate and cross the main road before another vehicle travelling at design
speed approaches it from main road.
NOTE: For safety consideration, the sight distance at uncontrolled intersection is
maximum of above three cases.
B. CONTROLLED INTERSECTION
• At signalized intersection, the above three requirements are not applicable.
• At rotary intersection, the sight distance should be atleast equal to SSD, for design
speed of rotary.
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Q. The sight distance available on a road to a driver at any instance depends on
1. Features of the road ahead
2. Height of the driver’s eye above the road surface
3. Height of the object above the road surface
a) 1 and 2 only
b) 1 and 3 only
c) 2 and 3 only
d) 1, 2 and 3.
[IES: 2020]
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HORIZONTALALIGNMENT OF HIGHWAY
• Change in direction is required in highway alignment due to the various reasons:
1. Topographic conditions
2. Obligatory points
• Various design elements to be considered in the horizontal alignment are:
1. Design speed
2. Radius of curve
3. Type and length of transition curve
4. Width of pavement
5. Superelevation
6. Set- back distance
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DESIGN SPEED
• The design speed is the main factor on which most of the geometric design
elements depends including horizontal alignment.
• The design speed of road depends upon class of road and terrain.
• Classification of terrain and design speed for different class of road are as follows:
Terrain Classification Cross slope (%)
Plain 0 – 10
Rolling 10 – 25
Mountaneous 25 – 60
Steep Above 60
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• Design speeds are also being defined for urban roads.
• Two values of the speed i.e. ruling and minimum are being specified for each type of road.
• As far as possible, an attempt should be made to design all the geometric elements for
ruling speed. However, if site conditions and economic considerations doesn’t permits so,
designing must be done for minimum design speed.
Type of road Design speed (kmph)
Plain Rolling Mountaneous Steep
Ruling Minimum Ruling Minimum Ruling Minimum Ruling Minimum
Expressway 120 100 100 80 80 60 40 60
NH and SH 100 80 80 65 50 40 40 30
MDR 80 65 65 50 40 30 30 20
ODR 65 50 50 40 30 25 35 20
VR 50 40 40 35 25 20 25 20
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HORIZONTAL CURVE
• It is a curve, in plan to provide change in direction to centre line of the road.
• It may be different in terms of:
a) Radius of the curve (m)
b) Degree of the curve: It is the central angle subtended by an arc of length 30m.
2πR
360o
=
30
D°
D° =
180°
πR
× 30 =
1720
𝑅
𝑹 =
𝟏𝟕𝟐𝟎
𝑫°
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• When a vehicle travels on horizontal curve, the centrifugal force acts horizontally
outwards through the CG of the vehicle.
• This centrifugal force depends upon speed of vehicle on a radius of horizontal
curve.
• It will be counteracted by lateral/ transverse
friction developed between the tyre and
pavement which helps the vehicle to change
direction along the curve.
Pc =
mv2
R
=
Wv2
gR
Here,
𝐏𝐜
𝐖
=
𝐯𝟐
𝐠𝐑
is termed as “Impact factor”
or “Centrifugal Ratio”.
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• The force acting on vehicle has the tendency to either overturn the vehicle
outwards about wheels and to skid the vehicle laterally outwards.
For stability of vehicles, both the conditions are to be checked as follows:
A. OVERTURNING EFFECT
For no overturning, MR ≥ Mo
MR = W ×
b
2
≥ Pc × h
Where, b = c/c distance of tyre
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𝐏𝐜
𝐖
= 𝐈. 𝐅. ≤
𝐛
𝟐𝐡
(Condition to prevent overturning)
If I.F. =
b
2h
: Vehicle is on verge of overturning
If I.F. >
b
2h
: Vehicle will overturn
B. TRANSVERSE SKIDDING EFFECT
For no skidding, FA + FB ≥ PC
μ(RA + RB) ≥ Pc
μW ≥ Pc
Pc
W
≤ μ or f
I.F. ≤ 𝛍 𝐨𝐫 𝐟
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NOTE: 1. If pavement is kept horizontal across the alignment, the pressure on the
outer wheel will be higher due to Pc acting outwards.
2. When the limiting condition for overturning occurs, the pressure on the inner
wheels becomes zero.
3. Since pressure on outer wheel is comparatively more, it damages the pavement by
the development of ruts over it.
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• Hence, to avoid both overturning and sliding,
𝐏𝐜
𝐖
≤ min (i)
𝐛
𝟐𝐡
(ii) f
The relative danger of lateral skidding and overturning depends upon whether ‘f’ is
lower or higher than
b
2h
.
If f <
b
2h
: Transverse skidding before overturning
If f >
b
2h
: Overturning before transverse skidding
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SUPERELEVATION
• In order to counteract the effect of centrifugal force, and to reduce the tendency of
the vehicle to overturn and skid, outer edge of pavement is raised w.r.t. inner
edges, thus providing a transverse slope throughout the length of the horizontal
curve.
• This transverse inclination to the pavement surface is known as “Superelevation/
Cant/ Banking”.
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E = Total superelevation height of outer edge
E = eB
ANALYSIS OF SUPERELEVATION
Forces acting on vehicles are:
1. Self- weight (W) (vertically downward)
2. Centrifugal force (Pc) (acting horizontally in outward direction)
3. Frictional force (F) (Laterally inward along the pavement surface)
For equilibrium condition, σ Fx = 0
Wsinθ + F1 + F2 = Pccosθ … … (i)
෍ Fy = 0
R1 + R2 = Wcosθ + Pcsinθ … . . (ii)
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From (i) and (ii), Pc cosθ − fsinθ = W sinθ + fcosθ
Pc
W
=
sinθ + fcosθ
cosθ − fsinθ
When θ is small, sinθ ≈ tanθ, cosθ ≈ 1
𝐈𝐦𝐩𝐚𝐜𝐭 𝐟𝐚𝐜𝐭𝐨𝐫 = 𝐂𝐞𝐧𝐭𝐫𝐢𝐟𝐮𝐠𝐚𝐥 𝐫𝐚𝐭𝐢𝐨 =
𝐏𝐜
𝐖
=
𝐭𝐚𝐧𝛉 + 𝐟
𝟏 − 𝐟𝐭𝐚𝐧𝛉
=
𝐞 + 𝐟
𝟏 − 𝐞𝐟
1-ef ≈ 1
𝐏𝐜
𝐖
= 𝐞 + 𝐟 =
𝐯𝟐
𝐠𝐑
𝐰𝐡𝐞𝐫𝐞 𝐯 𝐢𝐧
𝐦
𝐬
𝐞 + 𝐟 =
𝐕𝟐
𝟏𝟐𝟕𝐑
𝐰𝐡𝐞𝐫𝐞 𝐕 𝐢𝐧
𝐤𝐦
𝐡𝐫
R = Radius of curve (m)
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NOTE: 1. It may be seen that the contribution of superelevation ‘e’ (0.07) is much
less than that of lateral friction ‘f’ (0.15) in counteracting centrifugal force.
2. In some situations, eg- at intersection or some obstruction, it is not possible to
provide superelevation, in such cases, friction counteracts the centrifugal force and
if friction is also not sufficient, then radius of curve is increased which if not
possible, speed of vehicle negotiating a turn must be reduced to following:
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e + f =
𝑉2
127𝑅
When e = 0, 𝑉
𝑎 = 127𝑓𝑅
Where, Va = allowable speed
3. In some cases, superelevation may be negative, in such cases,
f – e =
𝑉2
127𝑅
4. e = f (V, R, f)
Hence, the value of e needed increases with increase in speed and with decrease in
radius of curve.
Hence, ‘e’ cannot be increased beyond a particular limit, as it would lead to the
toppling/ instability of slow moving vehicles with high CG, eg- bullock carts, truck,
lorry, etc.
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• Value of emax for different terrain are as follows:
• From drainage consideration, it is necessary to have minimum cross- slope to
drain out surface water.
• If ecalculated < cross- slope of road, then cross- slope may be provided as
superelevation only, by eliminating the crown and negative superelevation on
outer edge.
• In very flat curve with large value of Pc, and negative superelevation may be
permitted on outer edge.
Terrain type emax (%)
1. Plain and rolling 7
2. Mountaneous and steep: not bounded by snow 10
3. urban/ built- up area 4
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• As per IRC, radius of the curve beyond which ‘e’ is not required is as follows:
Design speed
(kmph)
Radius of horizontal curve (m)
4% 3% 2.5% 2% 1.7% (Camber)
20 50 60 70 90 100
25 70 90 110 140 150
30 100 130 160 200 240
35 140 180 220 270 320
40 180 240 280 350 420
50 280 370 450 550 650
60 470 620 750 950 1100
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DESIGN OF SUPERELEVATION
• Since, mixed traffic operates on our road, the superelevation design is very
complex.
• Providing a lower value of superelevation and relying on lateral friction would be
unsafe for fast moving vehicles and providing higher value of superelevation
creates problem for slow moving vehicles.
• Hence, a compromised value for ‘e’ is designed as follows:
Step-1: The superelevation is calculated for 75% of design speed, neglecting the
lateral friction
f = 0; Vdesign = 0.75V
e =
(0.75V)2
127R
=
V2
225R
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Step- 2: If the calculated value of e is less than 7%, so obtained ‘e’ is provided.
If value of ‘e’ obtained is more than 7%, then provide e = 7% and check for lateral
friction only (plain and rolling).
Step- 3: Check for friction developed for maximum value of e = 7% at full value of
design speed.
f =
V2
127R
− 0.07
If the value of ‘f’ calculated is less than 0.15, the superelevation of 7% is safe for
design but if it comes out to be more than 0.15, then the speed of vehicle has to be
restricted to safe value, which is less than design speed.
Step- 4: The allowable speed at the corner is computed as follows:
e + f =
V2
127R
0.07 + 0.15 =
Va
2
127R
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𝐕𝐚 = 𝟓. 𝟐𝟖 𝐑
Where, Va is in kmph and R is in m.
• If the allowable speed is higher than the design speed, then the design is adequate
but if it is less than design speed, the speed is limited to the allowable speed.
• Speed can be reduced by warning sign or by speed limit regulation signs.
• On important highways, speed is not reduced, hence, the curve should be re-
aligned with larger radius of curvature.
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ATTAINMENT OF SUPERELEVATION IN THE FIELD
• Introduction of superelevation on horizontal curve in the field is very typical as on
straight portion of road cross- section, normal camber is provided with crown at
the centre, sloping downwards on both the sides.
• But the portion of cross- section on circular curve is superelevated uniformly
sloping down from outer edge upto the inner edge of the pavement.
• The attainment of superelevation is done in two stages:
1. Elimination of the crown of camber section
2. Rotation of pavement to attain full superelevation
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STAGE- 1: ELIMINATION OF CROWN OF CAMBERED SECTION:
It can also be achieved by two methods:
a) In first method, outer half of the cross- slope is rotated about the crown at
desired rate, to attain the superelevation of inner half and centre line is not
altered.
b) In second method, (DIAGONAL CROWN METHOD), crown is shifted
progressively outwards, thus increasing the width of the inner half of cross-
section. (Negative superelevation is increased which is not safe for slow moving
vehicle).
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STAGE- 2: ROTATION OF PAVEMENT TO ATTAIN FULL
SUPERELEVATION:
• When the crown of the camber is eliminated, it does not signify the superelevation
desired at that section is attained.
• If desired superelevation is more than camber/ cross- slope, the pavement section
is rotated further till the desired elevation is attained.
• Desired superelevation can be attained by two methods:
1. By rotating the pavement cross- section about the centre line, depressing the
inner edge and raising the outer edge, each by half the total amount of
superelevation required.
2. By rotating the pavement cross- section about inner edge of the pavement
raising both centre as well as the outer edge of the pavement, such that the outer
edge is raised by full amount of superelevation desired.
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From 1 to 3, drainage problem will occur.
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• In cases where T- curve cannot be provided for some reason, two- third of
superelevation may be attained at straight portion before the start of the circular
curve and the balance one- third is provided at the beginning of the curve.
• The superelevation is introduced by the raising of outer edge of pavement at a rate
not exceeding 1 in 150 in plain and rolling, and 1 in 60 in mountaneous and
steep terrain.
Rotation about centre line Rotation about inner edge
1. It may interfere with drainage system 1. No interference with drainage system
2. Centre line remains unchanged 2. Centre line is elevated
3. earthwork is balanced in filling and cutting 3. Filling is required
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Q. If a road surface is adequately superelevated on horizontal curve, which one of
the following is the proper distribution of pressure on the vehicle wheels?
a) Pressure on both outer and inner wheels is equal.
b) Pressure on inner wheels is more than the outer wheels
c) Pressure on inner wheels is less than the outer wheels
d) Pressure on front wheels is thrice the pressure on rear wheels
[IES: 2007]
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Q. What is the maximum superelevation that is fixed by Indian Road Congress
(IRC) for roads in plain and rolling terrain and in snowbound areas, taking mixed
traffic into consideration?
a) 10.0%
b) 5.5%
c) 4.0%
d) 7.0%.
[SSC: 2018]
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Q. A superelevation ‘e’ is provided on a circular horizontal curve such that a vehicle
can be stopped on the curve without sliding. Assuming a design speed ‘v’ and
maximum coefficient of side friction ‘fmax’, which one of the following criteria
should be satisfied?
a) e≤fmax.
b) e > fmax
c) No limit of ‘e’ can be set
d) e =
1−(fmax)2
fmax
[GATE: 2017]
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Q. The rate of equilibrium superelevation on a road is:
1. Directly proportional to the square of vehicle velocity
2. Inversely proportional to the radius of the horizontal curve
3. Directly proportional to the square of the radius of the horizontal curve
Which of the above statements are correct?
a) 1 and 2 only.
b) 1 and 3 only
c) 2 and 3 only
d) 1, 2 and 3
[IES: 2018]
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Q. If superelevation is not provided on a horizontal curve of a highway, then on
which portion of the road, are pot holes likely to develop?
a) Outer edge of road.
b) Inner edge of road
c) Centre of road
d) Shoulder of road
[IES: 2010]
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Q. With all other relevant conditions remaining the same, the speed of a vehicle
negotiating a curve is proportional to
a) Weight of the vehicle
b) Weight of the vehicle
c)
1
Weight of the vehicle
d)
1
Weight of the vehicle
.
[IES: 2011]
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RADIUS OF HORIZONTAL CURVE
• Horizontal curve of highways are designed for specified design speed (ruling and
minimum).
• However, if this is not possible due to site conditions, then horizontal curve may
be re- designed.
• On the basis of speed, it is classified into following:
A. RULING MINIMUM RADIUS (RMR)
e + f =
V2
127RMR
𝐑𝐌𝐑 =
𝐕𝟐
𝐞𝐦𝐚𝐱 + 𝐟 𝟏𝟐𝟕
Where, V = Ruling design speed (kmph)
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B. ABSOLUTE MINIMUM RADIUS (AMR)
e + f =
V2
127AMR
𝐀𝐌𝐑 =
𝐕𝟐
𝐞𝐦𝐚𝐱 + 𝐟 𝟏𝟐𝟕
Where, V = Minimum design speed (kmph)
C. RADIUS BEYOND WHICH NO SUPERELEVATION IS REQUIRED
It is the radius corresponding to which camber serves the purpose of superelevation.
e = camber; f = 0; V = 75% Vd
𝐑𝐑𝐁𝐍𝐒 =
𝐕𝟐
𝟐𝟐𝟓 × 𝐂𝐚𝐦𝐛𝐞𝐫
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WIDENING OF PAVEMENT ON HORIZONTAL
CURVE
• On horizontal curve, which are not of very large radius, common practice is to
widen the pavement slightly more, than the normal width.
• The object of providing this extra widening on horizontal curve is as follows:
a) To avoid the off- tracking of vehicle:
• An automobile has a rigid axle and only the front wheels can be turned, hence
when the vehicle takes a turn to negotiate horizontal curve, the rear wheel do not
follow the same path as that of front wheel.
• If no lateral skidding of rear wheels takes place, the rear wheels follows the inner
path on the curve as compared to front wheels.
• This implies if inner front wheels takes a path on the inner edge of pavement on
horizontal curve, the inner rear wheels will be off the pavement of inner shoulder
and vice- versa.
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b) To encounter psychology of the driver:
To maintain clearance between the opposite moving vehicles or overtaking vehicle.
c) To avoid lateral skidding
d) To increase the visibility at the curve
NOTE: Extra widening is the function of length of wheel base (l), radius of curve
(R), and psychological factor.
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• The extra widening of the pavement on horizontal curve is divided into two parts:
a. Mechanical widening
b. Psychological widening
OFF- TRACKING OF THE VEHICLE:
R2
2 = R1
2 + L2
Also, R2 – R1 =Wm
Wm =
L2
2R2 − Wm
2R2 >> Wm, 2R2 – Wm ≈ 2R
Where, R = Radius of curve
𝐖𝐦 =
𝐋𝟐
𝟐𝐑
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For ‘n’ lane roads,
𝐖𝐦 =
𝒏𝐋𝟐
𝟐𝐑
NOTE: Hence, in a road having ‘n’ traffic lanes as ‘n’ vehicles can travel
simultaneously, Wm required will be more.
Length of wheel base = l = 6.1m
PSYCHOLOGICAL WIDENING
At horizontal curve, drivers have the tendency to maintain a greater clearance
between the vehicles, than a straight stretch of road. Therefore, an extra width is
required for this, which is given empirically by following relation:
𝐖𝐩 =
𝐕
𝟗. 𝟓 𝐑
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Where, V = design speed (kmph)
R = Radius (m)
Hence, total widening = We = Wm + Wp
𝐖𝐞 =
𝒏𝐋𝟐
𝟐𝐑
+
𝐕
𝟗. 𝟓 𝐑
NOTE: 1. For single lane road and two- lane road, if radius is greater than 300m,
then extra widening is not required.
2. For single lane road, psychological widening is not considered (Wp = 0).
3. Extra widening is provided gradually through transition curve.
4. Generally, extra widening is provided equally on both the sides of curve. But, on
hilly roads, extra widening is provided only on inner side.
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Extra width of the pavement at horizontal curve are as follows:
Radius of curve (m) ≤20m 20 – 40m 41 – 60m 61 – 100m 101 – 300m > 300m
Extra width on two-
lane road
1.5 1.5 1.2 0.9 0.6 -
Extra width on single
lane road
0.9 0.6 0.6 - - -
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The widening is introduced gradually starting from the tangent point, i.e. beginning
of T- curve at uniform rate equally on both sides in plain terrain and on inner side on
hilly terrain such that designed widening is attained at end of the transition curve.
On horizontal circular curve, without T- curve, two- third of the widening is
provided at the end of the straight portion and remaining one- third widening is
provided on circular curve.
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Q. Extra- widening of pavements provided because of off- tracking is known as:
a) Psychological widening
b) Mechanical widening.
c) Physical widening
d) Frictional widening
[SSC: 2018]
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HORIZONTAL TRANSITION CURVE
• T- curve is provided to change the alignment of pavement from straight to circular
gradually.
• The T- curve has a radius which decreases from infinity at the tangent point to the
designed radius of circular curve.
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OBJECTIVES OF PROVIDING THE TRANSITION CURVE
1. To introduce centrifugal force gradually over the vehicle.
2. To reduce the sudden jerk.
3. To introduce superelevation and extra widening gradually.
4. To improve the aesthetic appearance of road.
NOTE: 1. For an ideal T- curve, the length of the curve should be inversely
proportional to the radius.
𝐋 ∝
𝟏
𝐑
LR = constant
At TP, R = ∞, L = 0
At CC, R = Rc, L = Ls
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For transition curve to be provided, following options are available:
1. Spiral
2. Lemniscate
3. Cubical parabola
• All the three curves follow same path upto deflection angle of 4o and are almost
same upto 9o.
• In all these curves, radius decreases as length increases.
• But, the rate of change of radius or rate of change of centrifugal force is not
constant in case of lemniscate and cubical parabola.
• Hence, “Spiral curve” is used as transition curve as it fulfils the basic requirement
of ideal transition curve.
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LENGTH OF TRANSITION CURVE
Length of the transition curve is designed to fulfil three requirements:
A. RATE OF CHANGE OF CENTRIFUGAL FORCE
• Length of the transition curve is designed such that the rate of change of
centrifugal force is low.
• Rate of change of acceleration, c =
∆a
T
=
af−ai
T
=
(0.278V)3
LsRs
𝐋𝐬 =
𝟎. 𝟎𝟐𝟏𝟓𝐕𝟑
𝐂𝐑
Where V = Design speed (kmph)
• The maximum allowable value of rate of change of acceleration ‘c’ without
producing discomfort to the vehicle/ passenger is given by:
𝐜 =
𝟖𝟎
𝟕𝟓 + 𝐕
𝟎. 𝟓 − 𝟎. 𝟖 𝐦/𝐬𝐞𝐜𝟑
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B. RATE OF INTRODUCTION OF SUPERELEVATION (N)
Let rate of introduction of superelevation is 1V: NH
As per IRC:
1. 1:150 for Plain/ rolling terrain
2. 1:100 for built- up areas
3. 1:60 for mountaneous/ steep terrain
Hence, length of TC = Nx
Where, x = elevation of outer edge
CASE-I: If rotation is done about centreline
tanθ =
x
w + we
2
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𝐱 =
𝟏
𝟐
𝐞(𝐰 + 𝐰𝐞)
𝐋𝐬 =
𝟏
𝟐
𝐞 𝐰 + 𝐰𝐞 𝐍 =
𝐍𝐄
𝟐
CASE-II: If rotation is done about inner edge
tanθ =
x
w + we
X = e (w + we)
𝐋𝐬 = 𝑵𝒙 = 𝐞 𝐰 + 𝐰𝐞 𝐍 = 𝐍𝐄
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C. AS PER IRC
As per IRC, length of horizontal T- curve is given by following empirical
relationship:
a) For plain and rolling terrain:
𝐋𝐬 =
𝟐. 𝟕𝐕𝟐
𝐑
b) For mountaneous and steep terrain:
𝐋𝐬 =
𝐕𝟐
𝐑
Where, V= design speed (kmph)
Length of T- curve to be provided is maximum of three calculated from previous
criteria.
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Q. Which one of the following conditions is not correct with respect to transition
curve?
a) It should be tangential to the straight approaches at the two ends
b) It should meet the circular curve tangentially
c) Its curvature will necessarily be non- zero at the point of take- off from the
straight approaches.
d) The rate of increase of curvature along the transition reach should match with
the increase of cant
[IES: 2019]
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Q. Full amount of superelevation on a horizontal curve is provided at the
a) Beginning of the transition curve
b) Centre of the circular curve
c) End of the transition curve.
d) Centre of the transition curve
[IES: 2010]
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Q. The following purposes served by a transition curve in a highway alignment
include:
1. Gradual introduction of the centrifugal force on moving vehicles from zero on
the straight alignment to a constant final value on the circular curve
2. Enabling the gradual introduction of superelevation on the roadway
Select the correct answer using the codes given below:
a) 1 only
b) 2 only
c) Both 1 and 2.
d) Neither 1 nor 2
[IES: 2017]
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Q. An ideal horizontal transition curve is a:
a) Parabola
b) Circle
c) Spiral.
d) Hyperbola
[IES: 2012]
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Q. Which of the following are requirements for the design of a transition curve for a
highway system?
1. Rate of change of grade
2. Rate of change of radial acceleration
3. Rate of change of superelevation
4. Rate of change of curvature
Select the correct answer using the code given below:
a) 1, 2 and 3
b) 2, 1 and 4
c) 1, 3 and 4
d) 2, 3 and 4.
[IES: 2005]
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Q. Consider the following statements:
A transition curve is provided on a circular curve on a highway to provide:
1. Gradual introduction of centrifugal force
2. Minimum stopping sight distance
3. Gradual introduction of superelevation
4. Comfort and security to passengers
Which of the statements given above are correct?
a) 1, 2 and 3
b) 1, 3 and 4.
c) 2, 3 and 4
d) 1, 2 and 4
[IES: 2004]
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Q. The relationship between the length (l) and radius (r) of an ideal transition curve
is given by:
a) l ∝ r
b) l ∝ r2
c) l ∝
1
r
.
d) l ∝
1
r2
[GATE: 1999]
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SETBACK DISTANCE
• It is the clearance distance required from the centre line of pavement/ road to the
obstruction in order to maintain the adequate sight distance to the curve.
• The setback distance or clearance which is required from the centre line of
horizontal curve depends upon:
1. Required sight distance
2. Radius of horizontal curve
3. Length of the curve (Lcc)
CASE-I: When Lcc > SD
(a) For narrow roads such as single lane road:
O = Obstruction
AB = Sight line
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OD = m = setback distance
m = CD – CO = R – CO
Arc length AD = R×
α
2
α =
SD
R
×
180°
π
degrees
In ∆ACO,
cos
α
2
=
OC
R
CO = Rcos
α
2
m = R − Rcos
α
2
𝐦 = 𝐑 𝟏 − 𝐜𝐨𝐬
𝛂
𝟐
NOTE: SD is calculated along the centre line of road in single lane road
m = setback distance measured from centre line
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(b) Wide roads/ two or more lane roads:
• Here, the stopping distance is measured along the centre line of the inner lane and
the setback distance is measured from the centre of the road.
• Let ‘d’ be the distance between the centre line of the road and centreline of the
inside lane.
CA = R – d
CB = R – d
DO = m = setback distance
d =
w + we
4
α =
SD
(R − d)
×
180°
π
degrees
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Highway Engineering notes by jaspal singh sir.pdf

Highway Engineering notes by jaspal singh sir.pdf

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