Finding a probability method to determine the storage length of the left-turn lane at signalized intersections

Abstract

The storage length of left-turn lane is expressed as a function of the number of vehicles that can be stored during the effective red interval of signal left-turn phase. If the average expected number of vehicles(1) which will turn left is n, according to probability theory, the real number of vehicles that will arrive to the intersection and will turn left will not be exactly n. If the arriving left-turn cars are more than n, this will result in the left-turn lane overflow which in turn will block the through lane. The probability of the overflow occurring decreases with increasing of the left-turn lane storage length, and vice versa. This study seeks to find the relation between the left-turn storage length and the accepted probability of the overflow occurring. The accepted probability of the overflow occurring is based on the road importance. So, this relationship will lead to determine the storage length by determining the accepted probability of the spillover occurring.