Civil Engineering

# Overtaking Or Passing Sight Distance

The minimum sight distance needed by a driver on a two way road to be able him to overtake another vehicle ahead with safety against the traffic from the opposite direction, is called overtaking sight distance or say passing sight distance.

## Factors Affecting on Minimum Overtaking Sight Distance

The minimum overtaking sight distance depend upon the following factors:
• Speed of the overtaking, overtaken and the vehicle coming from opposite direction.
• Rate of acceleration of the overtaking vehicle.
• Spacing between the vehicle.
• Skill and reaction time of the driver.

## Analysis of Overtaking Sight Distance

Let, d1 = Distance traveled by the over taking vehicle ‘A’ during the reaction time t sec of the driver from position A1 to A2.

d2Distance traveled by the over taking vehicle ‘A’ from position A2 to A3 during the actual overtaking operation, in time T sec.

d3Distance traveled by the on coming vehicle ‘C’ from position C1 to C2 during the actual overtaking operation of A, in time T sec.

VB = Speed of the overtaken vehicle ‘B’ in m/sec.
S = Minimum spacing between the vehicle A and B.
Thus, d1 = VB . t
The minimum spacing (S) between the vehicle is given by the empirical formula:-
S = (0.7VB + 6) m
The distance covered by the overtaken vehicle B from position B1 to B2 during the overtaking operation in T sec is given by,
b = VB .T
d2 = 2S + b = VB .T + aT²/2
Where ‘a’ is acceleration of the vehicle A in m/Sec
Or, T = √ (4S/a)
Hence, d2 = 2S + VB .T & d3 = V.T
Where V is the design speed of vehicle C in m/Sec

### Overtaking Sight Distance Formula For Two way Traffic

Thus, for two way traffic overtaking sight distance(O.S.D)
= d1+d2+d3
= (V.t + 2S+ V.T + V.T) m

### Overtaking Sight Distance Formula For One way Traffic

Thus, for one way traffic overtaking sight distance(O.S.D)
= d1+d2
= (V.t + 2S+ VB .T ) m
If VB is not given then its value may be assumed as
VB = (V-4.5) m/Sec, Where V is the design speed in m/Sec.