Tractor Semitrailer Left Turns and Lane Changes 2010-01-0049

Data regarding the characteristics of left turns and lane changes performed by articulated tractor semitrailer combination vehicles in urban environments are presented. Previous studies have quantified acceleration rates for tractor semitrailers travelling straight, and for automobiles making left turns, but there is a gap in the literature regarding heavy vehicle acceleration during left turns. Likewise there is a lack of published data regarding the duration of lane changes made by these vehicles at highway speeds.

Left turns were studied at a four-way stop-sign controlled intersection with a high volume of heavy vehicle traffic. Markings were made on the roadway corresponding to three left turn paths of varying radii. Intervals leading up to and along the marked paths were measured and painted on the roadway. The motion of each tractor semitrailer that made the subject left turn was recorded by video. Video analysis allowed determination of distance, speed and acceleration associated with the vehicle paths. The distance from the limit line where the tractor semitrailers stopped prior to making the turn is also reported. Statistical analyses of vehicle position and velocity with time data suggest that the acceleration rate of the left-turning tractor semitrailers has three phases: an initial period of higher acceleration, followed by two periods of successively lower acceleration as the tractor completes the turn. Typical velocity time histories for wide, medium and tight turns is presented in a format of use to the reconstructionist.

Lane changes were studied on urban multi-lane freeways with speed limit of 55 mph for trucks. Video of the tractor semitrailers making lane changes was acquired from a car travelling in the same lane as the vehicle being studied. Timing of phases of the lane change maneuver and lateral (cross-lane) speed during the maneuver were determined by analysis of the video.