When calculating stopping sight distance, what deceleration rate does the AASHTO "Green Book" use?

The appropriate deceleration rate for stopping sight distance calculations, as specified in the AASHTO "Green Book," is based on the assumption of a typical passenger vehicle's ability to decelerate in an emergency situation. A deceleration rate of 11.2 feet per second squared is adopted as a standard to ensure a conservative estimate of the distance needed for a vehicle to come to a complete stop. This rate takes into account factors such as tire traction, road conditions, and vehicle dynamics.

Using this value ensures that roadway designs accommodate the safety needs of drivers under various conditions, thereby minimizing the risk of accidents. Incorporating this standard into stopping sight distance calculations allows engineers to create designs that are more effective at promoting safe stopping behavior, thereby enhancing overall traffic safety.