Question

Draw a sketch of a draw a typical cross-section of a 2-lane rural highway in a cut section and label all the components.

Answer 1

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.

1 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.

2 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.

3 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 traffic near the intersections is not affected by the bus-bay.

4 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 traffic in those lanes is not reduced.

5 Cycle track

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

6 Footpath

Footpaths are exclusive right of way to pedestrians, especially in urban areas. They are provided for the safety of the pedestrians when both the pedestrian traffic and vehicular traffic is high. Minimum width is 1.5 meter and may be increased based on the traffic. The footpath should be either as smooth as the pavement or more smoother than that to induce the pedestrian to use the footpath.

7 Guard rails

They are provided at the edge of the shoulder usually when the road is on an embankment. They serve to prevent the vehicles from running off the embankment, especially when the height of the fill 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 of vehicles.

Width of carriage way

Single lane	3.75
Two lane, no kerbs	7.0
Two lane, raised kerbs	7.5
Intermediate carriage	5.5
Multi-lane	3.5

Kerbs

Kerbs indicate the boundary between the carriage way and the shoulder or islands or footpaths.

Camber

Camber or cant is the cross slope provided to raise middle of the road surface in the transverse direction to drain off rain water from road surface. The objectives of providing camber are:

1. Surface protection especially for gravel and bituminous roads

2. Sub-grade protection by proper drainage

3. Quick drying of pavement which in turn increases safety

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 affect the vehicle operating cost, speed, riding comfort, safety, fuel consumption and wear and tear of tyres.

Right of way:-

Right of way is the area of land acquired for the road, along its alignment. It is the distance between the boundary stones on either side of the road.

Road shoulders:-

Shoulders are provided along the road edge to serve as emergency lane for vehicles. A per IRC, the minimum width of shoulders should be 2.5m.

Berm:- The distance between the road toe and the inner edge of borrow pit is called berm.

It prevents the erosion of embankment soil.

Clearance Distance (d3).

This is the distance between the passing vehicle at the end of its maneuver and the opposing vehicle. Based on various studies, this clearance distance at the end of the passing maneuver is assumed to be between 100 ft and 250 ft (30 m and 75 m).

Opposing Vehicle Distance (d4).

This is the distance traversed by an opposing vehicle during the time the passing vehicle occupies the left lane. the opposing vehicle appears after approximately one-third of the passing maneuver (d2) has been accomplished. The opposing vehicle is assumed to be traveling at the same speed as the passing vehicle.

1. Capacity Analysis. - Low Cost Methods for Improving Traffic Operations on Two-Lane Roads presents approximate adjustments that can be made to the capacity methodology in the Highway Capacity Manual. These adjustments can be used to estimate the levelof-service benefits from adding passing lanes to two-lane facilities.

2. Spacing. - When passing lanes are provided to improve the overall traffic operations over a length of roadway, they should be constructed systematically at regular intervals. Typical spacing for passing lanes may range from 3 miles to 10 miles (5 km to 15 km). Actual spacing of passing lanes will depend on the traffic volumes, right-of-way availability, and existing passing opportunities.

3. Location. -When determining where to locate passing lanes, the designer should consider the following factors:

a. Costs. - Locate passing lanes to minimize costs. Rough terrain will generally increase the costs for construction of passing lanes.

b. Appearance. - The passing lane location should appear logical to the driver. The value of passing lanes is more obvious to the driver at locations where passing sight distances are restricted or where opposing volumes are significant.

c. Horizontal Alignment.- Avoid locating passing lanes on highway sections with low-speed horizontal curves.

d. Vertical Alignment. -Where practical, construct passing lanes on a sustained upgrade. The upgrade will generally cause a greater speed differential between slow moving vehicles and passing vehicles. However, passing lanes in level terrain still should be considered where the demand for passing opportunities exceeds supply.

e. Sight Distance- Locate the passing lane where there will be adequate sight distance to both the entrance and exit tapers of the additional lane. Because of sight distance concerns, do not locate exit tapers just beyond a crest vertical curve.

4. Widths - Passing lane widths should be the same width as the adjacent travel lane width. Paved shoulder widths next to the passing lane should be a minimum of 4 ft (1.2 m).