On a road designed for a speed of 50 mph, what is the AASHTO minimum stopping sight distance?

The American Association of State Highway and Transportation Officials (AASHTO) provides guidelines for minimum stopping sight distance, which is a critical consideration in roadway design to ensure safety. For a road designed for a speed of 50 mph, the AASHTO recommends a minimum stopping sight distance that accounts for the perception-reaction time of the driver, as well as the braking distance needed to come to a complete stop.

At a speed of 50 mph, studies indicate that the required minimum stopping sight distance is approximately 425 feet. This distance allows a driver to perceive a hazard, react appropriately, and brake effectively. The calculation takes into consideration factors such as the driver's reaction time (typically around 2.5 seconds) and the deceleration rate (generally assumed to be about 11.2 feet per second squared for passenger vehicles).

In this context, the 425 feet provides an adequate margin of safety and is an established standard that helps ensure that vehicles can stop in time to avoid collisions with obstacles that may be in their path.