Characteristics of Emerging Road and Trail Users and Their Safety

Stopping Sight Distance

Adequate sight distance is required to provide path users ample opportunity to see and react to the unexpected. The distance required for a user to come to a complete stop, stopping sight distance, is a function of the user's perception and brake reaction time, initial speed, the coefficient of friction between the user's wheels and the pavement, and the braking ability of the user's device.

The critical trail user for stopping sight distance is the recumbent bicyclist. For wet pavement, AASHTO assumes the friction factor is half that of dry pavement. Although this would not affect the reaction time, it would double the braking distance. The calculated stopping sight distance on wet pavement would be 32.7 m (107 ft). In comparison, AASHTO currently recommends a stopping sight distance of 38.7 m (127 ft) for a bicyclist traveling at the recommended design speed of 30 km/h (20 mi/h) in a wet pavement condition (i.e., coefficient of friction considered to be half of dry pavement).