EFFECTS OF URBAN ROADWAY LANE BLOCKAGE ON CAPACITY

A recent study of incident management afforded opportunities to study the effects of incidents on surface street and on traffic flow. This paper reports the findings from these observations as headway measured from videotapes of 15 incidents made when incident-management personnel were present. In all cases, continuous queuing upstream of the blockage during videotaping reflected a maximum rate of flow that may be expected under the conditions. Mean headways for all observations was 2.40 seconds. Headways at crashes always were longer than those for traffic moving past disabled vehicles. One of the longest average headways occurred at the only nighttime observation, which was also an injury crash. The presence of a painted median facilitated lateral movement away from the incident and sped the flow. An analysis of variance revealed that the class of incident and the amount of activity at the scene had a substantial effect on the length of headways. However, time of day and presence or absence of a median also suggested a significant effect on mean headway.