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 depends upon the following factors:

Speed of the overtaking, overtaken and the vehicle coming from the opposite direction.
Rate of acceleration of the overtaking vehicle.
Spacing between the vehicles.
Skill and reaction time of the driver.

Analysis of Overtaking Sight Distance

Let, [latex] d_{1} [/latex] = Distance travelled by the overtaking vehicle ‘A’ during the reaction time t sec of the driver from position A1 to A2.

[latex] d_{2} [/latex] = Distance travelled by the overtaking vehicle ‘A’ from position A2 to A3 during the actual overtaking operation, in time T sec.

[latex] d_{3} [/latex] = Distance travelled by the on coming vehicle ‘C’ from position C1 to C2 during the actual overtaking operation of A, in time T sec.

[latex] V_{B} [/latex] = Speed of the overtaken vehicle in m/sec. S = Minimum spacing between vehicle A and B.

Thus, [latex] d_{1} [/latex] = [latex] V_{B} [/latex] . t

The minimum spacing (S) between the vehicle is given by the empirical formula:

S = (0.7 [latex] V_{B} [/latex] + 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 = [latex] V_{B} [/latex] .T

[latex] d_{2} [/latex] = 2S + b = [latex] V_{B} [/latex] .T + aT²/2 Where ‘a’ is acceleration of the vehicle A in m/Sec

Or, T = √ (4S/a)

Hence, [latex] d_{2} [/latex] = 2S + [latex] V_{B} [/latex] .T & [latex] d_{3} [/latex] = 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) = [latex] d_{1} + d_{2} + d_{3} [/latex]

= ( [latex] V_{B} [/latex] .t + 2S+ [latex] V_{B} [/latex] .T + V.T) m

Overtaking Sight Distance Formula For One way Traffic

Thus, for one way traffic overtaking sight distance(O.S.D) = [latex] d_{1} [/latex] + [latex] d_{2} [/latex]

= ( [latex] V_{B} [/latex] .t + 2S+ [latex] V_{B} [/latex] .T ) m

If [latex] V_{B} [/latex] is not given then its value may be assumed as [latex] V_{B} [/latex] = (V – 4.5) m/Sec, Where V is the design speed in m/Sec.