Highways - Component of Highways

What are the Components of Highways?

A component of highway means that item of work which is require to make the highway is. The components of the highway include the

1. Right of Way (RoW)

2. Roadway Width

3. Cross Slope or Camber

4. Carriageway or Pavement

5. Kerbs

6. Road Margins

 

These component is an equal important with compare to geometric design means geometrics component or element are design influenced by the psychology of the driver of the vehicles, the characteristics of the vehicle and the traffic of the highway. If we use all these component on skillful way, than highway safety is ensure.

Typical Drawing of Roadways

The basic components of a highway are explained briefly

1. Right of Way (RoW)

The right of way is the total land area acquired for the construction of the roadway along its alignment.

The right of way width is governed by:

-  Width of formation: It depends on the category of the highway and width of roadway and road margins.

-  Height of embankment or depth of cutting: It is governed by the topography and the vertical alignment.

-  Side slopes of embankment or cutting: It depends on the height of the slope, soil type etc.

-  Drainage system and their size which depends on rainfall, topography etc.

-  Sight distance considerations: On curves etc. there is restriction to the visibility on the inner side of the curve due to the presence of some obstructions like building structures etc.

-  Reserve land for future widening: Some land has to be acquired in advance anticipating future developments like widening of the road.

2. Roadway Width

Roadway land width is defined as the width of the road should be enough to accommodate all the elements of the roadway cross section, any future widening of the road and any public utility facilities that will be installed along the roadway. RoW is the area of the road acquired for carriages way + other necessities + future extension

3. Cross Slope or Camber

Cross Slope/camber is the slope that is provided in the transverse direction of the pavement or carriageway. The cross slope is provided to drain off the rainwater from the road surface. If we provide inadequate cross slope results in the flooding of water over the pavement, which results in deterioration of the highway.

The value of the slope is dependent on the type of rode, type of materials used for road construction and the severity of rainfall in the region. Generally, the value of cross slope varies from 2%-4%

4. Carriageway or Pavement

The portion or area of the highway or the road over which the traffic is meant to move is called the pavement or the carriageway. Width of the carriage way or the width of the pavement depends on the width of the traffic lane and number of lanes. Width of a traffic lane depends on the width of the vehicle and the clearance. Side clearance improves operating speed and safety.

The maximum permissible width of a vehicle is 2.44 and the desirable side clearance for single lane traffic is 0.68 m. This require minimum of lane width of 3.75 m for a single lane road. Traffic lane is defined as the carriageway or the or the pavement that is designed for the movement of one lane of traffic. However, the side clearance required is about 0.53 m, on both side and 1.06 m in the center. Therefore, a two lane road require minimum of 3.5 meter for each lane.

5. Kerbs

Kerbs indicate the boundary between the pavement and the shoulder. Curbs are desirable to be constructed for urban roads.

6. Road Margins

The portion of the road beyond the carriageway is known as road margin. Various elements that form the road margins road margin includes:

a)      Shoulders

b)      Bus Bays

c)      Parking lanes

d)     Sidewalks or footpaths

Shoulders: These are provided along the road edge and are intended for accommodation of stopped vehicles, serve as an emergency lane for vehicles and provide lateral support for base and surface courses. These also act as a service lane for the vehicles that have broken down.

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.

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.

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.

Footpath : Footpath 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 smoother than that to induce the pedestrian to use the footpath.