Driver Comprehension of the Circular Yellow Indication: Implications of Regional Variability

It has been postulated for some time that the indecision zone contributes to the occurrence of rear-end and right-angle crashes at signalized intersections. Much effort has been expended on the identification of situational factors that influence a driver’s behavior when presented a circular yellow indication (CY), and the construction of boundary descriptions for the region that the indecision zone occupies on the approach to the intersection. The notion that drivers comprehend the appropriate message from the CY is accepted without question. However, before the indecision zone can be fully understood or defined by transportation professionals, the assumption that drivers are correctly interpreting the intended message of the CY needs to be validated. This collaborative research effort between Oregon State University and the University of Massachusetts Amherst evaluated both the situational and literal comprehension of 130 drivers in Massachusetts (65 drivers) and Oregon (65 drivers) to acquire information on driver comprehension of the CY. Driver comprehension of the CY was categorized by three factors: identification of the intended message, the signal immediately following the CY, and the duration of the CY. Additionally, predictive behavior was analyzed for three factors: being the lead or following vehicle, being in one or two lanes, and relative distance from the stop bar. Statistically significant differences were determined between drivers in Massachusetts and Oregon regarding both comprehension and predictive behavior. Correct driver response occurred at a rate far lower than desirable. Thus, the results of study could contribute to improved educational and design procedures.