Evaluation of Performance Measures for Two-Lane Expressways in Japan

Abstract

Two-lane expressways exist as provisional sections for future expansion to four-lane expressways in Japan, although recently such roadway types have been considered for construction for permanent use. Their highway classification may fall somewhere between common (multilane) expressways and ordinary two-lane highways, with full access control and high speed limits but with only one lane per direction of travel. Since this type of highway is unique, methodologies for service level measurement of other uninterrupted-flow facilities are not applicable. Percent time spent following, for instance, is estimated with significant consideration of the opposing flow rate, which has practically no effect on driving conditions since a median barrier is present in all sections. The goal of this study is to analyze and compare possible performance measures that would best describe the traffic operational characteristics of two-lane expressways. Among the performance measures considered, follower density had much promise, having shown strong relationships with flow rate. Since the available data were only those taken during off-peak periods, further observations of follower flow must be made during congested or near-congested flow to establish follower density and volume relationships for all traffic conditions.