Overtaking Sight Distance | Overview and Calculation

Overtaking Sight Distance (OSD) is the sight distance required for the faster vehicle to overtake the slower vehicle safely.

It depends upon

  • Speed of overtaking vehicle, overtaken vehicle, opposing vehicle (undivided road)

  • Distance between these vehicles

As opposed to stopping sight distance, OSD is dependent on own vehicle's speed and the speed of the ahead vehicle, opposing vehicle as well. 

Overtaking Sight Distance Calculation

  • d₁ - Distance covered when we decide to overtake the slow moving vehicle

  • d₂ - Distance covered during overtaking operation

  • d₃ - Distance travelled by opposing vehicle (only in undivided road)

Overtaking Zone

When we are not able to provide OSD, we provide some zone (extra lane for certain distance) for vehicles to overtake slow moving vehicles.

  • Minimum length of Overtaking Zone = 3 times OSD

  • If overtaking zone cannot be provided, Intermediate sight distance - ISD (2 times SSD) is provided

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