Comparison of Infrastructure and In-Vehicle Driver Interfaces for Left-Turn Warnings

To examine the feasibility of driver–infrastructure interface (DII) and driver–vehicle interface (DVI) in the context of a left-turn assistance system, 20 test participants drove through a test-track intersection with oncoming traffic. Participants decided, both with and without the aid of a real-time warning, whether there was enough time to turn in front of oncoming traffic. This study examined both the effects of warning location (DII versus DVI) and the timeliness of the warning onset, while controlling for vehicle arrivals to the intersection as measured by an algorithm that predicted the spare time (trailing buffer) if the participant decided to turn in front of an oncoming vehicle. Lag (gap) acceptance increased as the predicted trailing buffer increased, with almost all lags with a predicted spare time greater than 1 s accepted and almost all lags with a predicted spare time fewer than −1.5 s rejected. The presence of warnings in either location resulted in a reduction in the turning rate, but there were no differences between warning locations. Most drivers preferred the DII in this instance, but based on participants’ feedback, a visual-only DVI located more central to the driver's focus of attention may also be acceptable. In regard to warning onset, information provided as decision support, rather than a preemptive or reactive warning, will likely need to be provided about 3.5 to 4.5 s before a driver reaches the intersection, to be integrated into the driver's decision process.