# Overtaking Or Passing Sight Distance

## 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.

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### 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 vehicle.
• Skill and reaction time of the driver.

### Analysis of Overtaking Sight Distance

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

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

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

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

Thus, $d_{1}$ = $V_{B}$ . t

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

S = (0.7 $V_{B}$ + 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 = $V_{B}$ .T

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

Or, T = √ (4S/a)

Hence, $d_{2}$ = 2S + $V_{B}$ .T & $d_{3}$ = 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)  = $d_{1} + d_{2} + d_{3}$

= ( $V_{B}$ .t + 2S+ $V_{B}$ .T + V.T) m

### Overtaking Sight Distance Formula For One way Traffic

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

= ( $V_{B}$  .t + 2S+ $V_{B}$ .T ) m

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