What is the purpose of a sight distance check in highway design?

• A. To ensure sufficient stopping distance for safe braking only.
• B. To measure roadside vegetation clearance.
• C. To ensure sufficient stopping or decision sight distance for safe driver reaction and stopping.
• D. To evaluate signage visibility at night.

Answer: (C)

Sight distance checks ensure there is enough visibility along the road for a driver to perceive a hazard, decide on an action, and safely execute it. This combines the time it takes to perceive and react with the distance needed to brake and stop, or to perform a safe maneuver, at the design speed, grade, and pavement conditions. In highway design, two concepts matter: stopping sight distance, the distance required to stop after seeing an obstacle, and decision sight distance, the longer distance needed for a driver to recognize the need to respond and then act safely. The purpose is to make sure the available sight distance meets these requirements so drivers can react in time and stop safely. It isn’t about clearing vegetation, measuring roadside clearance for non-safety reasons, or evaluating signage visibility at night.