Method of collection of traffic volume count data

Traffic volume count can be collected by the following methods:-

1. Manual counting:- In this method, a field team of enumerators (traffic persons) is deputed to record traffic volume on the prescribed record sheets in a specified period. A sample of the field sheet which is used for traffic counts.
   The main advantage of this method  is that the field team can record the type and direction of vehicles. However, it is not practicable to do manual counting for all the 24 hours of the day and on all days round the year. But this period is commonly used due to its specific advantage over the method of automatic recorders.
2. Automatic recorders :- In this method, the total number of vehicles crossing at a road intersection in the desired period is automatically recorded by a mechanical recorder. These recorders are either fixed type or portable type and may record the data by different methods discussed below.

• Photo electric cell method :- In this method, the automatic recorder is actuated by the interruption of a light beam falling on a photo electric cell placed on the road side as a vehicle passes.
• Electrical method :- In this method, the automatic recorder is actuated by closing of an electric circuit by the passage of a vehicle.
• Pneumatic method :- In this method, the automatic recorder is actuated by an air switch attached to a flexible hose pipe stretched across the road over which the vehicle passes.

          The main advantage of the methods of automatic recorders is that they can work throughout the day                      and night for the desired period, recording total hourly volume of traffic. But the disadvantage of this method is that the automatic recorders cannot record the type and direction of vehicles. Moreover, the data is not as accurate as  in case of manual counting since two or more vehicles going abreast will be recorded as a single unit.

     3.  Moving car method :- In this method, the number of vehicles met, overtaken and the time taken to     travel are noted by the observer moving in a car once against the traffic and second time alongwith the traffic. Then the volume of traffic is calculated by the following relationship:-

                                   V= x+y

                                         -----

                                         ta +tw

Where, V= Vehicles per minute in one direction.

            X= Number of vehicles met when moving against the desired direction in  ta  minutes.

            Y= Number of vehicles overtaken while moving alongwith the traffic in the direction in  tw minutes.

The accuracy of this method depends upon the number of tests conducted.

Purposes of Traffic Volume Study

Here is few purposes of traffic volume study:-

• To establish relative importance of any route or road facility.
• To decide the priority for improvement and expansion of a road and to allot the funds accordingly.
• To plan and design the existing and new facilities of traffic operations on the road.
• To make analysis of traffic pattern and trends on the road.
• To do structeral design of pavements and geometrically design of roads by classified traffic volume study.
• To plan one-way street and other regulatory measures by volume distribution study.
• To do design of road intersections, planning signal timings and channelisation by turning movement study.
• To do planning of side walks, cross walks and pedestrian signals by pedestrian volume study.
• To do economic studies after estimating the highway user's revenue.

Purposes Of Traffic Studies

Here is a few purposes

• To collect the data about type and volume traffic at present and to estimate the same that the road is expected to carry in near future.
• To determine the existing facilities such as traffic regulation and control intersection, etc. provided on roads so as to decide the priority for improvement and expansion of any particular road and to allot the funds accordingly.
• To decide the pavement thickness of the road.
• To decide geometrical design of the road.
• To design the drainage system, bridges, culverts, etc.
• To redesign the road widths, curves, traffic signals, intersections, etc. from the data collected after traffic surveys relating to accidents.
• To estimate the amount of the road taxes that can be levied.

Information To be Collected During Traffic Studies

The following information are usually collected during traffic studies:-

1. Type of traffic:- It means representation of traffic either by weight or by shape like trucks, buses, private cars, horse-driven vehicles, Single-bullock, double-bullock vehicles, motor cycles, auto-rickshaws, rickshaws, cycles or any other type of traffic.
2. Volume of traffic :- It means number of vehicles, persons or animals passing a given point on a road during a specified period of time and is usually expressed as vehicles per hour.
3. Nature of traffic :- It means whether the traffic is heavy during a certain period of the year due to some   festival or harvest or during certain time within the day when the office workers go and come back.
4. Pupose of traffic :- It means whether the traffic is of business type, recreation or the commodity carried.
5. Origin and destination of traffic :- It means the places from where traffic originates and where it terminates.
6. Speed of traffic :- It is recorded by means of traffic counters.
7. Conditions of traffic :- It means whether the vehicles are properly maintained or not.
8. Accidents :- It means collision of one road user with the other road user or with the fixed object lying within the road pavement. The data regarding the cause, time, location, and cost of every accident should be noted and recorded.
9. Any other information of special character :- It includes other necessary data collected during different traffic surveys relating to road, road usersand the environment.

What is Map Study or Paper Location?

The process of marking several possible alternative alignments of a road on the topographic map of the area is known as Map Study or Paper Location.
A topographic map shows the nature of the area by means of contour lines. This map also shows the position  of Obligatory points such as important towns, growing villages, trade and industrial centres, places of historic importance, canals, rivers, railway lines, bridges, etc. These maps are available from Survey Department of India with 15 or 30 m contour interval.
The possible alternative alignments are marked keeping in view the topographical and other features shown on the map.
The following consideration are made while marking a tentative alignment on the map :-

1. The route should be as short as possible.
2. It should be easy for construction, maintenance and traffic oppertions.
3. It should be safe for traffic operations.
4. It should also be economical in its cost of construction, maintenance and traffic operations.
5. It should be of maximum utility.
6. It should satisfy the maximum requirement of road geometrics.
7. It should fit in well the landscape.

What Is Road Drainage? Modes Of Water Penetration

The process of removing and controlling the access of surface and sub-surface water within the right-of-way of a road is called road drainage.

It also include interception ( collection ) and diversion of water from the road surface and the subgrade.
The process of interception and diversion of surface water through suitable side drains is called surface drainage, and the process of interception and removal of sub-soil water through suitable sub-surface drains is called sub-surface drainage.

The main object of road drainage is to keep the road surface and its foundation as dry as possible so as to maintain its stability.

Thus, a good drainage system is essential for efficient highway transportation with minimum maintenance cost.

Modes of water penetration into road structure.

The following are the different modes of water penetration into the road structure:-

1. Surface water from the top of pavement by percolation through caracks and poor pavement surface.
2. surface water from sides of the pavement.
3. sub-soil water from underside of the pavement by capillary rise.
4. sub-soil water from sides of the pavement.
5. Intercepted water due to overflooding of cross drainage works.

Types Of Earth Roads

Earth roads are of the following two types:-

1) Ordinary earth roads :- The earth road having its foundation and wearing surface consisting of one or two compacted layers of natural soil available along its alignment is called an ordinary earth road.
This is the lowest form of pavement surface used so far and is considered as the first stage in the development of road pavement construction. The surface of these roads is generally dusty and ruts are quickly formed. These roads become unserviceable very soon an thus require frequent repair in order to keep them in serviceable condition for a longer period.

2) Stabilized earth roads :- The earth road having its foundation and wearing surface consisting of one or two compacted layers of stabilized soil is called stabilized-earth road.
This is the improved form of earth roads. These roads can carry greater traffic, load and provide better better service as compared to ordinary earth roads.

Construction Of Earth Roads

Earth roads are constructed as detailed below :-
Material required :- The materials required for the construction of an ordinary earth road are natural soil, originally availableat site, a suitable stabilizer, if required. The ideal composition of soil which is recommended for construction earth roads.

Method of construction of an ordinary earth road :- The construction work of an ordinary earth road is completed in the following steps ;-

1. Preparing the subgrade :- The subgrade is prepared and the surface is brought to the required camber and gradient.

2. Rolling an watering :- The surface is rolle properly and well wetted with water.

3. Spreading the soil :- after watering, a layer of graded soil, about 10 cm thick is evenly spread.

4. Rolling :- the layer of soil is rolled at optimum moisture moisture content ( OMC ) with a suitable roller and finally finished with a light roller.

The type of roller for compaction is decided based on soil type, desired amount of compaction and availability of equipment. Atleast 95 per cent of dry density of its light compaction is considered desirable.
Note :- Sometimes, a second layer (about 10 cm thick ) is also spread and rolled properly to act as wearing course.
5. Checking :-The camber of the finished surface is checked an corrected, if necessary.
6. Curing :- The rolled surface is watered for four or five days for curing. No traffic should be allowed to pass over the road surface during this period.
7. Opening to traffic :- After curing, the traffic is allowed to pass but the surface is sprinkled over with water for a period of 10 to 1 days.
Method of construction of a stabilized earth road :- construction work of a stabilized earth road is completed  in steps as described in case of ordinary earth road. for constructing  a stabilized earth road, the subgrade is prepared to the required camber and gradient. Then the base course is prepared by any suitable method of soil stabilized soil ( about 10 cm thick ) is spread over the base course and rolled properly. The surface is then cured and opened to traffic.

Requirements Of A Good Road Aggregate

Road aggregate forms the princpal material in the construction of road pavements. Therefore, it should be of good quality. A good road aggregate should fulfill the following requirements:-

1. Hardness :- A good road aggregate should be sufficiently hard i.e. it should offer maximum possible resistance to abrasion.
This requirement of the road aggregate is particularly needed when it is to be used in flexible pavements. Since flexible road pavements go on distorting under heavy traffic  load,  the road metal is constantly but slightly disturbed. This causes pieces of stones to rub and grind against each other. Therefore, the road aggregate should be hard enough to resist abraison due to grinding of pieces of  stones against each other.

2. Toughness :- A good road aggregate should be quite tough i.e. it should offer the maximum possible resistance to the hammering effect of wheel loads.
This requirement is essential so that the road aggregate used in the construction of flexible pavements can resist the impact caused due to movements of heavy traffic loads without breaking into smaller pieces.

3. Durability :- A good road aggregate should be sufficiently durable i.e. it should be sufficiently resistant to weathering agencies.
This requirement of the road aggregate is essential so that it can resist the effects of weathering agencies like rain, variation of temperature, frost, etc. in order to achieve long life of the road pavement.

4. Strength :- a good road aggregate should have high crushing strength.
This requirement of the road aggregate is essential so that it can withstand safely the stresses developed in the road pavement due to traffic wheel loads.

5. Cementation :- a good road aggregate should have sufficient cementation property i.e. it should have sufficient binding property within itself.
This requirement is essential for road aggregate used in the water bound macadam road surfaces. in such roads, the road aggregate should form its own binding material under the load of road roller and bind itself so that  the road pavements may remain serviceable for a longer period.

6. Adhesiveness :- A good road aggregate should have adhesive property i.e. it should have sufficient binding capacity with the binders.
This requirement is essential of road aggregate used in the bituminous roads. In such roads, the road aggregate should have adequate binding capacity with the binders like bitumen, asphalt. coaltar, etc. so as to ensure stability of the road surface.

Types Of Curves On Hill Roads

The following are the important types of curves provided on hill Roads:-

1. Hair-Pin Curves ;
2. Salient Curves ;
3. Re-entrant Curves.

1. Hair-pin curves :- The curve in a hill road which changes its direction through an angle of 180 degree  or so, downthe hill on the same side is known as hair-pin curve.

A Hair-Pin Bend

This curve is so called because it conforms to the shape of a hair-pin. The bend so formed at the hair-pin curve in a hill road is known as hair-pin bend. This type of curve should be located on a hill side having the minimum slope and maximum stability. It must also be safe from view point of land slides and ground water. Hair-pin bends with long arms and farther spacing are always preferred. They reduce construction problems and expensive protective works. Hair-pin curves or bends of serpentine nature are difficult to negotiate and should, therefore, be avoided as far as possible.

2. Salient curves :- The curves having their convexity on the outer edges of a hill road are called salient curves.

The centre of curvature of a salient curve lies towards the hill side. This type of curve occurs in the road length constructed on the ridge of a hill. the bend so formed at the salient curve in a hill road known as corner   bend.

Salient curves are very dangerous for fast moving traffic. At such a curve or at corner bend, the portion of projecting hill side is usually cut down to improve the visibility as shown in fig. (re-entrant curve). The outer edge of the road at such a curve is essentially provided with a parapet wall for protection of the vehicles from falling downthe hill slope.

3. Re-entrant curves :- The curves having their convexity on the inner edge of a hill roadare called re-entrant curves.

Re-entrant curves

The centre of curvature of a re-entrant curves lies away from the hill side. This type of curve occurs in the road length constructed in the calley of a hill.

These curves are less dangereous as they provide adequate visibility to the fast moving traffic. At such curves, the parapet wall is provided only for safety of fast moving traffic.