Effect of restricted sight distances on driver behaviors during unprotected left-turn phase at signalized intersections

During the unprotected left-turn green phase at intersections on divided highways, if the median of the major road is relatively wide, the simultaneously turning vehicles in the opposing left-turn lanes often block drivers’ views for each other so as to influence the unprotected left-turn or U-turn gap acceptance behaviors. To identify the changes of those driving behaviors clearly associated with drivers’ restricted sight distances, a field data collection in this study was conducted at a signalized intersection with the potential sight distance problem. Both linear regression and logistic regression models were developed to estimate parameters of gap acceptances. The results showed that sight obstruction due to the opposite turning vehicles may contribute to significant increments of the critical gap and follow-up time. This could result in an extra traffic delay and a capacity reduction in the left-turn lane. Moreover, it was found that left-turn or U-turn drivers with the sight distance problem were more likely to accept smaller gaps so as to cause more traffic conflicts between turning traffic and opposing-through traffic. The analyses in this paper provide a better understanding of the relationship between highway visibility and traffic safety and operation.