## 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 + aT**²**/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.

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