Analysis of Bottleneck Capacity and Traffic Safety in Japanese Expressway Work Zones

This paper explores the characteristics of both bottleneck capacity and traffic safety in work zones of an 150 km two-lane section on the Tomei Expressway in Japan. It is found that vertical sag in a work zone could be a major bottleneck in addition to the transition area of the work zone. The capacity of bottleneck sags tends to be smaller than that of the transition area. It also tends to decrease with the length of the one-lane section upstream of a bottleneck. The bottleneck capacity during closures of outer lane and inner lane is much the same in daytime and the former seems to be less than the latter in nighttime due to the negative effect of the narrow lateral spacing of the inner lane in nighttime.

The traffic accident analysis of work zones shows more than 70% of the total accidents and more than 90% of the total injury and fatal accidents occur during traffic congestion. Focusing on the injury and fatal accidents occurred in congested work zones, about half of them happen at the back of the queue and about 40% even in the section upstream of work zones. The accident rate in congested work zones is about 8 times as high as in non-congested ones. This study also highlights the locations of high accident rates in both congested and non-congested work zones.

Based the study results, some countermeasures are recommended to mitigate traffic congestion and improve traffic safety in work zones.