Merging Taper Lengths for Lane Closures of Short Duration

The merging taper lengths described in the Manual on Uniform Traffic Control Devices are assumed to apply to roadways of all types. Yet driver expectations and traffic operations differ greatly between the high-speed freeway and the lower-speed, signalized urban street. The research described in this paper investigated the operational impacts of reduced taper lengths on lower-speed urban arterials. The study found that drivers did react differently after merging taper lengths were modified. Both the merging taper and the work vehicle in the closed lane served as visual cues to drivers to vacate the closed lane. On longer taper lengths, channelizing devices were used to motivate drivers to change lanes. Vehicles with occluded views, however, were more likely to become trapped and to create mobility issues in the traffic stream. On shorter taper lengths, drivers reacted to the merging taper and the work vehicle itself. Although fewer vehicles became trapped near the merge point, that point was much closer to the work vehicle. Under the absence of taper conditions (i.e., mobile operations), in which the work vehicle was much larger than the trucks used during the merging taper observations, fewer drivers remained in the closed lane at comparable locations. Both motorist and worker safety must be considered in the selection of an appropriate merging taper length for work activities of shorter duration on urban arterials. Further research should investigate the implications for worker safety of installing and removing various merging taper lengths as compared with the time it takes to complete the work activity.