IMPROVED PROTECTED-PERMITTED LEFT-TURN SIGNAL DISPLAYS - THE TEXAS APPROACH

The advantages of protected-permitted left-turn signal operation and of lead-lag left-turn sequencing are noted, as well as the conflict in using a combination of these techniques, namely, the 'trap' problem. An alternative operation has been developed in Dallas, Texas for protected-permitted left-turn signals used concurrently with lead-lag phasing. This method allows the waiting left turner to see ball indications which clear at the same time as the opposing through traffic, and therefore drivers do not make false assumptions. The basic concepts involved in the operation are described. The Texas Department of Transportation conducted an internal evaluation of the safety and effectiveness of the operation, and it has now become the method used for most dual and quad left-turn signal applications in Dallas.