OPERATIONAL EFFECTS OF NONTRAVERSABLE MEDIANS AND TWO-WAY LEFT-TURN LANES: A COMPARISON

Two popular arterial highway cross-section designs--two-way left-turn lanes (TWLTLs) and nontraversable medians (NTMs, raised or depressed) on four-lane roads--are compared for operational efficiency under identical traffic and development situations. Two broad measures of operational effectiveness, delay and fuel consumption, are obtained through simulation performed using the TRAF-NETSIM model. A three-way factorial design is used to compare and contrast the variables of interest. The results suggest that driveway density, traffic volume on the arterial, and type of design (TWLTL or NTM) have a significant effect on the performance measures such as total delay, fuel consumption, and delay to left-turning traffic and through traffic on the arterial. At low driveway density and low traffic volume, the difference in total delay between the two designs is not found to be significant. At higher driveway densities, no significant difference in delay to left-turning traffic on the arterial can be expected between TWLTL and NTM. However, TWLTL design is found to cause less delay to through traffic and be more fuel efficient at all levels of driveway density and traffic volume.