As mentioned in the objectives of geometric design of highways, there are certain important characteristics of vehicles that would affect the design of roads. The two main parameters of vehicles are the dimension of the vehicle and the weights of the vehicle.
Important Characteristics of Vehicle for Geometric Design of Highways
- Width of the Vehicle: The width of the traffic lanes and shoulders, and the parking space is influenced by the width of the vehicle.
- Height of the Vehicle: The clearance that is provided for the overhead structures like bridges, overhanging branches of road side trees and the electrical lines are dependent on the height of the vehicle.
- Overall Length of Vehicle: Overall length of a vehicle influences the design of bridges, the horizontal curves, the valley curves and safety regulations.
- Vehicle Load: The vehicle load influences the design of bridges, the thickness of the pavement and the design of ruling gradient.
- Vehicle Speed: The vehicle speed affects the design of:
- Super elevation
- Limiting radius
- Sight distances
- Width of pavement in straights and curves
- Provision of guard rails
- Width of shoulder
- Protection of railroad crossing
- Treatment of inter-sections
- Capacity of a lane for traffic
Also Read: What is Camber in Road Construction?
Dimensions of Road Vehicle in Geometric Design of Highways
Both passenger vehicle and trucks can be carried by a highway. Hence, the design standards are developed to maintain these requirements. Here, the dimensions and weights of trucks are governed as they are higher in value compared to passenger vehicles.
As per Indian Road Congress (IRC), the maximum dimensions of road vehicles are given below. The width, height and length is specified.
More than two units and similar combination must exist and that their length must not exceed 18 m, as shown in Figure above.
Weight of Road Vehicle in Geometric Design of Highways
The weight of the vehicle is defined in terms of axle load.
Axle load is defined as the total load that is transmitted to the road by all the wheels, whose centers are included between 2 parallel vertical planes that are 1 m apart and are traverse to longitudinal axis of the vehicle.
The load on single axle must not exceed 102 kN.
The load on tandem axle must not exceed 180 kN.
The Gross Load of a Vehicle or combination of vehicles should not be greater than ‘W’. Where,