MIDBLOCK U–TURN FACILITIES ON MULTILANE DIVIDED HIGHWAYS: AN ASSESSMENT OF DRIVER’S MERGING GAP AND STOP DELAYS

Abstract

This paper discusses the results of a study which was carried out with a primary objective to evaluate the merging gaps and traffic delays at midblock U–turn facilities installed on multilane divided highways. A total of more than 2,000 U–turn drivers at a midblock U–turn facility on an urban multilane highway were observed using a camera–video recording technique. The data pertaining to the analysis of gap acceptance and rejection was abstracted from the video–playbacks using a computer event recording program. The analysis found that the critical gap of the drivers at a midblock U–turn facility is in the range of 4.0 – 4.5 seconds, which is different from the values reported for studies carried out in other countries. The effect of major road traffic volumes on the stop delays to the U–turn drivers could not be established because the data did not exhibit any specific trend. The drivers were observed to make forced merging maneuvers when traffic volumes in the main traffic stream are relatively heavy. Such maneuvers lead to flow breakdown in the major road to occur at a faster rate. The findings suggest that there is a need for a thorough study to be carried out to evaluate the current practice of U–turn facility design and assessment methods since traffic operations at such a facility is different from those at on–ramp facilities where their planning and design are generally based on the American Highway Capacity Manual.