Question

Explain the elements of highway geometric design

Answer 1

The geometric design of highways deals with the dimensions and layout of visible features of the highway. The emphasis of the geometric design is to address the requirement of the driver and the vehicle such as safety, comfort, efficiency, etc. The features normally considered are the cross section elements, sight distance consideration, horizontal curvature, gradients, and intersection. The design of these features is to a great extend influenced by driver behavior and psychology, vehicle characteristics, traffic characteristics such as speed and volume. Proper geometric design will help in the reduction of accidents and their severity. Therefore, the objective of geometric design is to provide optimum efficiency in traffic operation and maximum safety at reasonable cost. The planning cannot be done stage wise in this case like that of a pavement, but has to be done well in advance. The main components that will be discussed are:

Factors affecting the geometric design,

Highway alignment, road classification,

Pavement surface characteristics,

Cross-section elements including cross slope, various widths of roads and features in the road margins.

Sight distance elements including cross slope, various widths and features in the road margins.

Horizontal alignment which includes features like super elevation, transition curve, extra widening and set back distance.

Vertical alignment and its components like gradient, sight distance and design of length of curves.

Intersection features like layout, capacity, etc.