Designed Speed

• Design speed of vehicles depends upon the type of road over it eg.NH,SH,MDR,ODR,VR.

• Design speed of vehicles help in deciding the cross-sectional elements : width,clearance, SD, radius of curve, superelevation, transition gradient and length of submit etc.

Topography

• The topography of terrain conditions influence the design speed, then in turn soverns the designing of highway elements(as above).

For eg.
In plain terrain on SH permissible design speed is 100 km whereas the same speed on rolling terrain is permitted to 80 kmph & mountainous terrain is 50kmph 

Traffic Factors

• Traffic factors contain vehicle characteristic and human characteristic

• In order to design highway element standard size of vehicle is considered (car) in mixed traffic operation

• Human characteristics include physical & psychological features of drivers & pedestrians.