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An innovative operation known as "Dallas Phasing" eliminates the potentially unsafe "yellow trap" situation by allowing a continued permissive left turn during the opposite approach lagging protected left-turn phase. Research has shown that this operation reduces delay and improves safety. The animation below illustrates the "yellow trap" when the east-bound driver in the yellow car makes a permitted left turn on a yellow assuming that opposing traffic is also yellow. A separate animation shows how PPLT ("Dallas Display") solves the "yellow trap".
The research under NCHRP Project 3-54 (Phase I) found that a variety of PPLT traffic controls (seven basic forms) exist and that there has been limited research devoted to understanding the relative effectiveness of these forms of control. There have been concerns that some may be confusing to motorists, and the need exists to validate the relative operational advantages and safety aspects of the various left turn controls. Specifically, there is need for research to address the yellow trap and driver confusion problems. In addressing these problems, it will be necessary to consider the safety implications of increased signal efficiency and the difficulty in establishing uniformity between states. [Back] [Continue] to Objectives |
