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Intermediate sight distance shall be kept equal to
SSD
2xSSD
3xSSD
5xSSD
2xSSD
Intermediate Sight Distance (ISD) is defined as the distance provided on a highway where overtaking is not possible or safe, but a driver must have enough sight distance to safely stop in the event of an obstruction. According to IRC (Indian Roads Congress) standards, it is taken as twice the Stopping Sight Distance (SSD).
Intermediate Sight Distance (ISD) is defined as the distance provided on a highway where overtaking is not possible or safe, but a driver must have enough sight distance to safely stop in the event of an obstruction. According to IRC (Indian Roads Congress) standards, it is taken as twice the Stopping Sight Distance (SSD).
ISD=2├ЧSSD тАФ Defines the relationship between Intermediate Sight Distance and Stopping Sight Distance
The principle relies on the assumption that on single-lane roads where Overtaking Sight Distance (OSD) cannot be provided throughout, providing ISD ensures that a vehicle can stop if it encounters an oncoming vehicle. By setting ISD=2├ЧSSD, the design ensures that two vehicles approaching each other from opposite directions each have sufficient distance to apply brakes and come to a complete stop before a collision occurs.
ISD is mandatory on single-lane roads where OSD is not provided.
It acts as a compromise between SSD and OSD in restrictive geometric conditions.
It ensures safety during head-on meeting scenarios on two-way traffic.
SSD is the minimum sight distance required to stop the vehicle safely.
Economical alternative to providing full OSD on every section of the road.
Improves road safety on single-lane highways.
Does not permit safe overtaking.
Restricts the overall traffic flow capacity compared to sections with OSD.
Single-lane two-way highways.
Mountainous roads where providing full OSD is technically or financially unfeasible.
The value of SSD is calculated using the formula SSD=vтЛЕt+2g(f┬▒0.01n)v2тАЛ.
Options C and D are incorrect as they deviate from the standard IRC recommended multiplier.
B is correct тАФ Intermediate sight distance is kept equal to twice the Stopping Sight Distance (2├ЧSSD).
Always remember that ISD is specifically for safe stopping when meeting oncoming traffic, whereas OSD is for passing slow vehicles; don't confuse the two in exam calculations.