With increasing urbanization, especially in suburban areas, will come more four/plus-lane divided arterials. Such arterials contain medians that vary in size. Field studies have shown that wide medians tend to complicate the left turning maneuver of vehicles moving from major roads onto minor streets. The increase in median width increases the likelihood of sight-distance restrictions due to the opposing left-turn vehicles. When a left-turning vehicle is confronted by an opposing left–turning vehicle, the result is the creation of a blind zone for both vehicles. Drivers attempting this turn during an unprotected signal phase may unintentionally accept a small gap because they can’t see the opposing through-vehicles concealed in the view-blocked area. Acceptance of even a very small gap could contribute to potential traffic conflicts and possibly serious angle collisions. Moreover, inadequate sight distance may cause cautious drivers to reject physically adequate gaps because they need more time to make sure that the opposing through lanes are clear; this can lead to needless delays for the left-turning traffic. The goal of this research was to improve intersection sight distances and traffic operation, especially for left-turn drivers attempting turns during the unprotected phase at signalized intersections. Specific objectives included the following: • develop geometric models to calculate sight distance for those drivers under different geometric configurations; • advance understanding of the relationship between highway visibility and traffic operation, specifically, left-turn capacity; • identify the changes of gap-acceptance behavior clearly associated with restricted sight distances due to the opposing left-turn vehicles (through a field study) (Author/publisher)
Abstract