# 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

### 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)

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### 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