Perceptual-Motor Control Strategies for Left-Turn Execution

The purpose of the present study was to investigate the perceptual-motor strategies used by drivers during left-turn execution as a means of identifying potential causes of such accidents and to inform the design of left-turn warnings. Twenty-one participants executed a series of left turns in a driving simulator. The initial distance (D) and time to intersection (TTI) of an oncoming vehicle were varied orthogonally to present drivers with a range of different safety margins. The initial distance values ranged from 50 to 150m, and the TTI values ranged between 4 to 12 sec. Accidents occurred on roughly 3% of the trials, with large individual differences in performance. The most common conditions for accidents to occur involved a large value of D(>=100) and a medium-short value of TTI(<=6). The timing of left-turn initiation was significantly affected by both the TTI and the distance of the oncoming vehicle. On average, left turns were initiated at a shorter TTI when the distance was large. The authors conclude that since there were several instances in which drivers used the unsafe strategy of basing their decision to turn on the distance of the oncoming vehicle, a left-turn warning that is based on temporal information alone (e.g., Nowakowski, 2006) will likely be unreliable, because the decision to turn is not solely based on temporal information.