Overtaking Sight Distance
Overtaking is a necessary operation because all the vehicles do not travel with a uniform speed. The overtaking sight distance is the minimum distance open to the vision of driver of a vehicle intending to overtake the slow moving vehicle ahead safely against the traffic in opposite direction. It is measured along the center line of road over which driver with his eye level 1.2 m above the pavement surface can see the top of an object of height 1.2 m above the road surface.
Factors affecting the overtaking sight distance,
- Speed if overtaking, overtaken and opposite direct traffic.
- The space between overtaking and overtaken vehicle.
- Reaction time of driver.
- Gradient of road
where,
A1 Vehicle = Travelling at the design speed of highway,
B1 Vehicle = Slow moving vehicle,
C1 Vehicle = Vehicle travelling in the opposite direction.
Overtaking Sight Distance = d1 + d2 + d3
where,
d1 = Distance travelled by overtaking vehicle A during the reaction time t sec.
d2 = Distance travelled by the vehicle A during the actual overtaking operation in time T seconds.
d3 = Distance travelled by the vehicle C comes from the opposite directions.
Distance - d1
Initially speed of vehicle A = VA and VA was more than VB, but while looking for opportunity to enter into opposite lane, vehicle A follows vehicle B and hence, VA = VB.
hence,
Distance - d2
Distance - d3
OSD,
VB and VC in kmph
T in Sec
OSD in meter
If VB is not given, then assume
VB = v - 4.5 m/s
VB = V - 16 kmph
