PAVEMENT SURFACE CHARACTERISTICS

​Pavement surface characteristics

For safe and comfortable driving four aspects of the pavement surface are important; the friction between the wheels and the pavement surface, smoothness of the road surface, the ight re ection characteristics of the top of pavement surface, and drainage to water.
Friction
Friction between the wheel and the pavement surface is a crucial fact in the design of horizontal curves and thus the safe operating speed. Further, it also a ect the accelerati n and decele ation ability of vehicles.
Lack of adequate friction can cause skidding or slipping f vehicles.
Skidding happens when the path traveled along the r ad surface is m  re than the circumferential
movement of the wheels due to friction
Slip occurs when the wheel revolves more than the corresponding longitudinal movement along the
road. Various factors that a ect friction are:
Type of the pavement (like bituminous, concrete, gravel),
Condition of the pavement (dry or wet, hot or cold, etc),

The frictional force that develops between the wheel and the pavement is the load acting multiplied by a factor called the coe cient of friction and denoted as f . The choice of the value of f is a very complicated issue since it depends on many variables. IRC suggests the coe cient of longitudinal friction as 0.35-0.4 depending on
the speed and coe cient of lateral friction as 0.15. The former is useful in sight distance calculation and the latter in horizontal curve design.

Unevenness:
It is always desirable to have an even surface, but it is seldom possible to have such a one. Even if a road is constructed with high quality pavers, it is possible to develop unevenness due to pavement failures. Unevenness a ect the vehicle operating cost, speed, riding comfort, safety, fuel consumption and wear and tear of tyres.
Unevenness index is a measure of unevenness which is the cumulative measure of vertical undulations of the pavement surface recorded per unit horizontal length of the road. An unevenness index value less than 1500 mm/km is considered as good, a value less than 2500 mm.km is satisfactory up to speed of 100 kmph and values greater than 3200 mm/km is considered as uncomfortable even for 55 kmph

Light reflection:
White roads have good visibility at night, but caused glare during day time. Black roads has no glare during day, but has poor visibility at night Concrete roads has better visibility and less glare
It is necessary that the road surface should be visible at night and reaction of light is the factor that answers it.

Drainage:
The pavement surface should be absolutely impermeable to prevent seepage of water into the pavement layers. Further, both the geometry and texture of pavement surface shou d he p in raining out the water from the surface in less time.

TYPES OF SIGHT DISTANCE

​Types of sight distance:

Sight distance available from a point is the actual distance along the road surface, over which a driver from a speci ed height above the carriage way has visibility of stationary or moving objects. Three sight distance situations are considered for design:
Stopping sight distance (SSD) or the absolute minimum sight distance

Intermediate sight distance (ISD) is de ned as twice SSD Overtaking sight distance (OSD) for safe overtaking operation

Head light sight distance is the distance visible to a driver during night driving un er the i umination of
head light
Safe sight distance to enter into an intersection.

The most important consideration in all these is that at all times the iver t ave ing at the design speed of the highway must have sufficient carriageway distance within his line of vision to a ow him to stop his vehicle before colliding with a slowly moving or stationary object appearing suddenly in his wn t afficlane.
The computation of sight distance depends on:
Reaction time of the driver:


Reaction time of a driver is the time taken from the instant the bject is visible to the driver to the instant when the brakes are applied. The total reaction time may be split up into f ur c mponents based on PIEV theory. In practice, all these times are usually combined into a total perception-reaction time suitable for design purposes as well as for easy measurement. Many of the studies shows that drivers require about 1.5 to 2 secs under normal conditions. However, taking into consideration the variability of driver characteristics, a higher value is normally used in design. For example, IRC suggests a reaction time of 2.5 secs. Speed of the 
vehicle
The speed of the vehicle very much a ects the sight distance. Higher the speed, more time will be required to stop the vehicle. Hence it is evident that, as the speed increases, sight distance also increases.

Efficiency of brakes:
The efficiency of the brakes depends upon the age of the vehicle, vehicle characteristics etc. If the brakeffciency is 100%, the vehicle will stop the moment the brakes are applied. But practically, it is not possible to achieve 100% brake efficiencyTherefore the sight distance required will be more when the e ciency of brakes are less. Also for safe geometric design, we assume that the vehicles have only 50% brake efficiency.

KERBS

​Kerbs:

Kerbs indicate the boundary between the carriage way and the shoulder or islands or footpaths. Di erent types of kerbs are (Figure 12:3):
Low or mountable kerbs : This type of kerbs are provided such that they encourage the trafficto remain in the through trafficlanes and also allow the driver to enter the shoulder area with little di culty. The height of this kerb is about 10 cm above the pavement edge with a slope which allows the vehicle to climb easily. This is usually provided at medians and channelization schemes and also helps in longitudinal drainage.
Semi-barrier type kerbs : When the pedestrian trafficis high, these kerbs are provided. Their height is 15 cm above the pavement edge. This type of kerb prevents encroachment of parking vehicles, but at acute emergency it is possible to drive over this kerb with some di culty.

Barrier type kerbs : They are designed to discourage vehicles from leaving the pavement. They are provided when there is considerable amount of pedestrian tra c. They are placed at a height of 20 cm above the pavement edge with a steep batter.

Submerged kerbs : They are used in rural roads. The kerbs are pr vided at pavement edges between the pavement edge and shoulders. They provide lateral c n nement and stability to the pavement.

Road margins: 
The portion of the road beyond the carriageway and on the roadway can be generally called road margin. Various elements that form the road margins are given below.

Shoulders:
Shoulders are provided along the road edge and is intended for accommodation of stopped vehicles, serve as an emergency lane for vehicles and provide lateral support for base and surface courses. The shoulder should be strong enough to bear the weight of a fully loaded truck even in wet conditions. The shoulder width should be adequate for giving working space around a stopped vehicle. It is desirable to have a width of 4.6 m for the shoulders. A minimum width of 2.5 m is recommended for 2-lane rural highways in India

Parking lanes:
Parking lanes are provided in urban lanes for side parking. Parallel parking is preferred because it is safe for the vehicles moving on the road. The parking lane should have a minimum of 3.0 m width in the case of parallel parking.

Bus-bays:
Bus bays are provided by recessing the kerbs for bus stops. They are provided so that they do not obstruct the movement of vehicles in the carriage way. They should be at least 75 meters away from the intersection so that the trafficnear the intersections is not a ected by the bus-bay.

service roads:
Service roads or frontage roads give access to access controlled highways like freeways and expressways. They run parallel to the highway and will be usually isolated by a separator and access to the highway will be provided only at selected points. These roads are provided to avoid congestion in the expressways and also the speed of the trafficin those lanes is not reduced.

Cycle track:

Cycle tracks are provided in urban areas when the volume of cycle trafficis high Minimum width of 2 meter is required, which may be increased by 1 meter for every additional track.

Footh path:
Footpaths are exclusive right of way to pedestrians, especially in urban areas. They are provi ed for the safety of the pedestrians when both the pedestrian trafficand vehicular trafficis high. Minimum wi th is 1.5 meter and may be increased based on the tra c. The footpath should be either as smooth as the pavement or more smoother than that to induce the pedestrian to use the footpath.

Gaurd rail:
They are provided at the edge of the shoulder usually when the r ad is n an embankment. They serve to prevent the vehicles from running o the embankment, especially when the height f the ll exceeds 3 m. Various designs of guard rails are there. Guard stones painted in alternate black and white are usually used. They also give better visibility of curves at night under headlights f vehicles.

LUCKNOW ROAD CONGRESS

​Lucknow road congress 1984:

This plan has been prepared keeping in view the growth pattern envisaged in va i us elds by the turn of the century. Some of the salient features of this plan are as given bel w:
This was the third 20 year road plan (1981-2001). It is also called Luckn w ad plan.
It aimed at constructing a road length of 12 lakh kilometres by the year 1981 resulting in a road density of 82kms/100 sq.km
The plan has set the target length of NH to be completed by the end of seventh, eighth and ninth ve year plan periods.
It aims at improving the transportation facilities in villages, towns etc. such that no part of country is farther than 50 km from NH.
One of the goals contained in the plan was that expressways should be constructed on major trafficcorridors to provide speedy travel.
Energy conservation, environmental quality of roads and road safety measures were also given due impor-tance in this plan.

BOMBAY ROAD CONGRESS

​Bombay road congress 1961

The length of roads envisaged under the Nagpur plan was achieved by the end of it, but the road system was de cient in many respects. The changed economic, industrial and agricultural conditions in the country warranted a review of the Nagpur plan. Accordingly a 20-year plan was drafted by the Roads wing of Government of India, which is popularly known as the Bombay plan. The highlights of the plan were:
It was the second 20 year road plan (1961-1981)
The total road length targeted to construct wasWorldabout10lakhs.
Rural roads were given speci c attention. Scienti c methods of construction was proposed for the rural roads. The necessary technical advice to the Panchayaths should be given by State PWD’s.
They suggested that the length of the road should be increased so as to give a oad ensity of 32kms/100 sq.km
The construction of 1600 km of expressways was also then included in the p an.

NAGPUR ROAD CONGRESS

​Nagpur road congress 1943:

The second World War saw a rapid growth in road trafficand this led to the deterioration in the condition of roads. To discuss about improving the condition of roads, the government convened a conference of chief engineers of provinces at Nagpur in 1943. The result of the conference is famous as the Nagpur plan.
A twenty year development programme for the period (1943-1963) was nalized. It was the rst attempt to prepare a co-ordinated road development programme in a planned manner.
The roads were divided into four classes:
National highways which would pass through states, and places having national importance for strategic, administrative and other purposes.
B) State highways which would be the other main roads of a state.
C) District roads which would take trafficfrom the main roads to the interior of the district . According to the importance, some are considered as major district roads and the remaining as other district roads.
{Village roads which would link the villages to the road system.
The committee planned to construct 2 lakh kms of road across the country within 20 years.
They recommended the construction of star and grid pattern of roads throughout the country.
One of the objective was that the road length should be increased so as to give a road density of 16kms per 100 sq.km

HIGHWAY DEVELOPMENT AND PLANNING

Overview

Road transport is one of the most common mode of transport. Roads in the form of trackways, human pathways etc. were used even from the pre-historic times. Since then many experiments were going on to make the riding safe and comfort. Thus road construction became an inseparable part of many civilizations and empires. In this chapter we will see the diWorlderentgenerationsofroadandtheircharacteristicfeatures. Also we will discuss about the highway planning in India.

History of highway engineering
The history of highway enginnering gives us an idea about the roads of ancient times. Roa s in Rome were constructed in a large scale and it radiated in many directions helping them in mi ita y ope ations. Thus they are considered to be pioneers in road construction. In this section we will see in detail about Ancient roads, Roman roads, British roads, French roads etc.
Ancient Roads
The rst mode of transport was by foot. These human pathways w uld have been developed for speci c purposes leading to camp sites, food, streams for drinking water etc. The next maj mode of transport was the use of animals for transporting both men and materials. Since these loaded animals required more horizontal and vertical clearances than the walking man, track ways emerged. The invention of wheel in Mesopotamian civilization led to the development of animal drawn vehicles. Then it became necessary that the road surface should be capable of carrying greater loads. Thus roads with harder surfaces emerged. To provide adequate strength to carry the wheels, the new ways tended to follow the sunny drier side of a path. These have led to the development of foot -paths. After the invention of wheel, animal drawn vehicles were developed and the need for hard surface road emerged. Traces of such hard roads were obtained from various ancient civilization dated as old as 3500 BC. The earliest authentic record of road was found from Assyrian empire constructed about 1900 BC.
Roman roads
The earliest large scale road construction is attributed to Romans who constructed an extensive system of roads radiating in many directions from Rome. They were a remarkable achievement and provided travel times across






2.7 m Sloping Wearing Surface 5cm thick
Shoulder Slope 1:20
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Side drain _
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Transportation engineering syallubus

CHAPTER 1 HIGHWAY DEVELOPMENT AND PLANNING

Highway development in india
Necessity for highway planning
Different road development plans
Classification of roads
Road network patterns
Highway Alignment
Factors affecting alignment
Engineering surveys
Drawing and reports
Highway project.

CHAPTER 2 HIGHWAY GEOMETRIC DESIGN
Importance of Geometric Design
factors affecting highway geometric design Design controls and Criteria-
Highway Cross Section Elements-Sight Distance Elements-Stopping sight Distance, Overtaking Sight Distance Intermediate Sight Distance Design of Horizontal Alignment Design of Super elevation
Extra widening
Design of Transition Curves Design of Vertical alignment Gradients-
Vertical curves

CHAP ER 3 RAFFIC ENGINEERING AND REGULATION
Basic Parameters of raffic Volume, Speed and density
Traffic volume studies-Data collection and presentation Speed studies –Data collection and presentation-Origin and Destinations studies,
Parking Studies
Onstreet and offstreet parking Road Accidents –
Causes and Preventive measures Accident Data Recording
Condition Diagram and Collision Diagrams Traffic Signs – Types and Specifications Road markings-Need for Road Markings Types of Road Markings-
Design of Traffic Signals- Webster method.


CHAPTER 4 INTERSECTION DESIGN
Types of Intersections
Conflicts at Intersections
Requirements of At –Grade intersection-
Types of at-Grade Intersections-
Chanalization -Traffic Islands
Types of Grade Separated Intersections
Rotary Intersection –concept of Rotary
Design factors of rotary
Advantages and limitations of rotary intersections.

CHAPTER 5 HIGHWAY MATERIAL, CONSTRUCTION ANDMAINTENANCE:
Highway material characterization Subgrade soil
Stone aggregate Bitumen materials
Construction of gravel road
Construction of water bound macadam road Construction of bituminous pavements Surface dressing
Bitumen bound macadam Bituminous concrete
Construction of cement concrete pavements Construction of joints in cement concrete pavements Joint filter and seal
Pavement failures Maintenance of highways Highway Drainage.