Vehicle Behavior on Deceleration Lanes

This paper presents an analysis and evaluation of vehicle flow characteristics on rural deceleration lanes. Site observations were conducted by means of video photography, tape‐switches for transmitting speed information, and, for braking information, by hidden observers. Findings indicated considerable differences between commonly accepted assumptions of the AASHTO model for deceleration lane length determination and actual vehicle behavior. Major points include: (1) Average speeds of diverging vehicles at start of deceleration lanes were lower than average speeds of through vehicles; (2) deceleration values, for deceleration in gear and while braking, were lower than values suggested by AASHTO; and (3) average initial deceleration in gear lasted three times as long as the value currently assumed for design purposes. A model was then formulated to determine deceleration lane length, based on average freeway and exit ramp running speeds.