LEAD AND LAG LEFT TURN SIGNALS
THE MOST COMMON TYPES OF EXCLUSIVE LEFT TURN CONTROL ARE DESCRIBED, INCLUDING SINGLE LEFT TURNS OF BOTH LEAD AND LAG VARIETY, AND SEVERAL ARRANGEMENTS FOR DUAL OPPOSING LEFT TURNS. A LEAD LEFT TURN SEQUENCE WAS DEFINED WITH THE SUGGESTION THAT IT SHOULD BE HANDLED BY A SEPARATE LANE SIGNAL AND AN EXCLUSIVE LANE IN ORDER TO MEET ACCEPTABLE SAFETY STANDARDS. ALSO DEFINED WAS A LAG LEFT TURN SEQUENCE, WITH THE COMMENT THAT IT SHOULD REQUIRE PROHIBITING THE OPPOSING LEFT TURN FOR SAFETY REASONS. IT WAS SUGGESTED THAT AN EXCLUSIVE LEFT TURN INTERVAL SHOULD BE AVOIDED IF THE AVERAGE NUMBER OF LEFT TURNS MADE ON YELLOW AND RED DURING THE PEAK HALF HOUR DOES NOT EXCEED TWO PER SIGNAL CYCLE. ALSO EXPLORED WERE THE WAYS IN WHICH PROGRESSIVE MOVEMENT IN AN INTERCONNECTED SIGNAL SYSTEM CAN BE ENCHANCED BY THE INTELLIGENT SELECTION OF A LEAD OR A LAG (OR LEAD-LAG) LEFT TURN SEQUENCE, DEPENDING ON THE RELATIVE POSITION OF THE SIGNAL WITH RESPECT TO THE MEETING POINTS OF PLATOONS. FOR DUAL LEFT TURNS IT WAS CAUTIONED THAT SPLIT OR INDEPENDENT TIMING OF LEFT TURN PHASES MAY BE REQUIRED IF LEFT TURN DEMAND IS DIRECTIONALLY PREFERENTIAL AT DIFFERENT PEAK PERIODS. /AUTHOR/
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Supplemental Notes:
- Vol 38, No 7, PP 50, 52-53, 56&
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Authors:
- Mckay, B W
- Publication Date: 1968-4
Media Info
Subject/Index Terms
- TRT Terms: Highway safety; Lead time; Lead-lag phasing; Left turns; Peak periods; Red interval (Traffic signal cycle); Safety factors; Traffic delays; Traffic signals; Turning traffic
- Uncontrolled Terms: Timing; Turning movements
- Subject Areas: Highways; Operations and Traffic Management; Safety and Human Factors;
Filing Info
- Accession Number: 00225206
- Record Type: Publication
- Files: TRIS
- Created Date: May 24 1994 12:00AM