COMPARISON OF LEFT-TURN ACCIDENT RATES FOR DIFFERENT TYPES OF LEFT-TURN PHASING

Left-turn accident rates are compared for five types of left-turn phasing: permissive; leading exclusive/permissive; lagging exclusive/permissive; leading exclusive; and lagging exclusive. Two different study designs were used to compare left-turn accident rates; both a simple comparison design and a simple before-and-after design were used. Left-turn accident rate (number of left-turn accidents per million left-turning vehicles) is used to compare the relative safety of the different types of left-turn phasing. Left-turn accident rates are shown for each type of left-turn phasing and are further subdivided by whether there are two or three lanes of opposing traffic, by left-turn volume, and by opposing volume. The before-and-after data are categorized according to the types of left-turn phasing in the before and after periods. Observations and conclusions are made about the effect of volume, number of lanes of opposing traffic, and type of left-turn phasing on the accident rate.