Ordered Probit Modeling of User Perceptions of Protected Left-Turn Signals

Abstract

There is an absence of nationally accepted warrants for left-turn phasing at signalized intersections. Some guidelines recommend a protected left-turn phasing for turns with three or more opposing through lanes. However, there is no research that justifies this recommendation. A Web-based motorist survey was conducted to find how motorists perceive difficulty and their preference for protected left-turn signalization vis-a-vis the number of opposing lanes. The ordered probit modeling of 2,017 responses suggests that driver perception of difficulty to make turns without protected left-turn signals increases with intersection size. As high as 91% of the respondents stated that they much or extremely prefer a protected left-turn signal at an intersection where left-turn vehicles have to cross three lanes of opposing through traffic. The ordered probit models also provide indications of the effects of various sociological variables on the probabilities of driver perceptions of difficulty and preference. The estimated models provide a sensitive tool for making decisions about the left turn treatment at signalized intersections.