No abstract

PURPOSES :Climbing lanes on expressways managed by the Korea Expressway Corporation (KEC) have been hot potatoes due to conflicts between slow-moving vehicles such as trucks and other vehicles at the merging section as well as the less popularity with the slow-moving vehicles. In order to resolve such problems, KEC has altered existing climbing lanes to passing-type climbing lanes in 1999. The new type of climbing lanes showed an apparent improvement in mobility. For example, the speeds of vehicles using both climbing lane and other lanes improved a lot. However, there has been no clear evidence about improved safety. METHODS :This research effort was initiated to evaluate the safety of the new passing-type climbing lanes using the comparison-group(C-G) method based on three-year-long traffic accident data sets before and after the change, respectively. RESULTS :The passing-type climbing lanes showed twice increased traffic accidents even though the traffic accidents on old type climbing lanes increased 1.1% during the same periods. In addition, in-depth study, the merging area of the passing-type climbing lanes was found out to be the weakest section where 43.8% traffic accidents out of total traffic accidents happened. It is noted that the merging area of the old type climbing showed only 25.0% traffic accidents. CONCLUSIONS :The new passing-type climbing lanes were found to be weak in terms of safety when compared with the old type climbing lanes. Especially, the merging area should be improved to reduce the risk of traffic conflicts between slow-moving vehicles and other vehicles.

The level of service (LOS) of the Highway Capacity Manual (KHCM) has been used as a basic criterion at decision making processes for signalized intersections in Korea. The KHCM provides five steps for the signalized intersection analysis. Among them, lane grouping, which is the third step, significantly influence the final LOS. The current method presented in the KHCM, however, classifies a shared lane as a de facto turning lane group, even though the turning traffic of the shared lane is few. Thus, this research was initiated to provide an alternative. To this end, three alternatives were suggested, including the method based on the lane grouping presented in the U.S. Highway Capacity Manual, the method using turning ratio of shared turning lane, and the method using a threshold traffic volume in lane grouping. The feasibilities of the three methods were evaluated using a calibrated CORSIM model. Conclusively, the method using a threshold traffic volume in lane grouping outperformed.