INTERSECTION DELAY AND LEFT TURN PHASING

OVER THE PAST TEN YEARS THE ROAD DEPARTMENT AND OTHER AGENCIES IN LOS ANGELES COUNTY HAVE INSTALLED MINOR MOVEMENT LEFT TURN PHASING AT NUMEROUS SIGNALIZED INTERSECTIONS. WHEN TRAFFIC VOLUMES AT SIGNALIZED INTERSECTIONS INCREASE, THE PROBLEM OF PROVIDING LEFT TURN PROTECTION SIMILARLY INCREASES. THREE LOCATIONS ARE ANALYZED AFTER DELAY STUDIES ARE USED TO FIND HOW MUCH INTERSECTION DELAY INCREASED AFTER LEFT TURN PHASING WAS INSTALLED. CONCLUSIONS INDICATED THAT: (1) INTERSECTION DELAY PER VEHICLE SUBSTANTIALLY INCREASED FROM 22% TO 121% AFTER LEFT PHASING WAS INSTALLED, (2) PEAK HOUR DELAY MAY INCREASE OVER 100% AFTER LEFT TURN PHASING IS INSTALLED ON ALL APPROACHES OF THE INTERSECTION, (3) LEFT TURN DELAY IS NOT SUBSTANTIALLY REDUCED BY LEFT TURN PHASING, AND (4) NORMALLY, INTERSECTION DELAY COSTS OUTWEIGH ACCIDENT REDUCTION SAVINGS, BUT ACCIDENT SAVINGS SHOULD BE CONSIDERED FOR EACH INDIVIDUAL INTERSECTION. /AUTHOR/