Traffic volume and waiting time influence on gap acceptance of selected change direction U-turn opening

The vehicles moving on change direction U-turn opening have to spend some time while the acceptable headway provided on conflicting main traffic flow. The present paper investigated the effect of waiting time and traffic volume increasing on gap acceptance behavior, critical gap limit, and U-turn capacity. The data were collected at selected change direction U-turn in Najaf city (center city of the Najaf governorate located approximately 160 km south of Baghdad, the capital of Iraq) within Najaf city highways network. The study concentrated on the passenger cars driver movement at change direction U-turn openings. The analysis approach depended on evaluating these parameters and their degree of influence on U-turn capacity is statistical analysis. statistical analysis established that, when waiting time fall in a range between 21- 30 sec, driver enforced to accept gap size less than that fall in the range of 11 to 20 sec at a confidence interval of 95%. On the other hand, there is a slightly different in mean gap acceptance between an interval of (1-10) and (11-20) sec) at the same confidence interval. Results showed the studied U- turn change direction median critical gap equal to 3.75 sec. and follow-up time was 1.1 seconds. According to Siegloch’s formula the maximum capacity of 3273pcu/ hr. At level of confidence of 95%, the mean value of the highest wait time group interval is lower than the critical gap. Therefore, the studied change direction U-turn might be hazard location and it is important to control and manage at the median opening