Design of Super Elevation

For mix traffic condition is complex problem as vehicle is moving with different speed. For fast moving vehicle, providing higher super elevation without considering coefficient of friction is safe (i.e. f = 0) i.e. centrifugal force is fully counter balanced by weight of vehicle. 

For slow moving vehicle, providing lower value of super elevation considering coefficient of friction is safe i.e. centrifugal force is balanced by weight of vehicle and coefficient of friction both.

By considering both type of moving vehicle, IRC suggested to use 75 % design speed for designing super elevation and considering f=0.

Steps:

1. Calculate super elevation for 75 % design speed with f=0 for mixed traffic condition,

if,

e < = e max     - OK

e >  e max       - provide e = e max and check for f 

2. If e > e max then provide e = e max and check for f

f < = 0.15     - OK

if  f  > 0.15    - go to 3rd step

3. If f  > 0.15 , then restrict speed or minimum radius (i.e. ruling radius)