Abstract
Understanding how drivers exit freeways and interact with deceleration speed-change lanes (SCL) and ramp controlling features is important for adequate design of exit ramp terminals that meet drivers' expectations and needs. Therefore, this paper investigates drivers' diverging behavior along exit ramp terminal segments, including freeway right lane (FRL), SCL, and ramps based on video-based trajectory data collected using unmanned aerial vehicles (UAVs). Trajectories of 3,259 vehicles were collected at six sites as the vehicles moved on the FRL or SCL and off-ramp. Diverging behavior measures, including diverging speed, diverging location, deceleration rate on SCL, SCL utilization, and speeds at ramp gore nose and end of the SCL, were then extracted and used for the qualitative and quantitative analysis. The qualitative analysis showed that drivers exiting a freeway at taper-type SCLs tended to start deceleration on the FRL, which impacted the speeds of nonexiting vehicles. On the other hand, this behavior was not evident at parallel-type SCLs. Additionally, drivers were found to adopt a single overall deceleration rate from the diverge point to the end of deceleration. Finally, observations of data confirmed the importance of accounting for the effects of ramp controlling features on the diverging behavior and vehicle deceleration needs at freeway exit ramp terminals. The paper suggests that the design of deceleration SCLs should take into consideration the effect of ramp controlling features in the design of deceleration SCLs.