This project produced NCHRP Report 395
. The report presents procedures for estimating the operational, safety, and access impacts of different midblock left-turn treatments and includes guidelines for selecting among raised-curb medians, two-way left-turn lanes, and undivided cross sections. The report will be useful to designers of multilane roads with unrestricted access.
Midblock left-turn lane treatments, which are important in meeting the access needs of motorists, directly affect accidents and roadway capacities. Although the safety records of multilane cross sections with flush or raised medians are generally well known, there were few, if any, studies that provided explicit information and data on the capacity and operational effects of these facilities. Research was needed to provide guidelines and criteria for selecting appropriate midblock left-turn lane treatments.
The objective of this project was to develop a quantitative methodology for evaluating alternative midblock left-turn lane treatments on urban and suburban arterials. The project results are applicable to a full range of arterial cross sections, including raised medians and up to 7-lane flush cross sections. The product of this study is in the form of a guide that allows the transportation practitioner to make decisions based on commonly available data. The research also produced a better understanding of the relationship between the type of midblock left-turn lane treatment and the adjacent traffic generators.