Impact of Signal Mounting Configurations on red-light running at urban Signalized Intersections

by Kerrie l. schAttler, ph.d., deborAh mcAvoy, ph.d., p.e., ptoe, mAtthew t. christ, msce, And collette m. glAuber introduction Navigating through signalized intersections is considered to be one of the most complex driving tasks. In 2007, the National Highway Traffic Safety Administration (NHTSA) reported that 8,650 people were killed as a result of intersection-related crashes.1 A high proportion of these intersection-related crashes involved red-light running. NHTSA estimates that approximately 800 fatality crashes are directly related to motorists running red lights at signalized intersections annually.1 Many engineering strategies have been found to reduce red-light running and related crashes and injuries, such as improving signal visibility, improving signal conspicuity, optimizing signal timings, changing cycle lengths, changing the timing of yellow and all-red intervals, using dilemma zone protection, removing unwarranted signals, improving stopping conditions such as converting intersections to roundabouts, and others.1, 2 In order to achieve safe and smooth traffic flow at intersections, traffic signal visibility and conspicuity is critical to reducing red-light running and associated crashes. In a recent survey, 40 percent of motorists caught running red lights indicated that the reason for their violation was that they did not see the signal, whereas another 12 percent thought the signal indication was green, instead of red.3 In regards to standards, the Manual on Uniform Traffic Control Devices (MUTCD) regulates the location (horizontal and vertical placement), design (size and number of signal faces by approach), and meaning of the signal indications. These standards are in place to ensure uniformity in signal design features throughout the United States. However, there are substantial differences in the mounting configurations of traffic signals among road agencies. Traffic signals may be mounted on poles located on street corners, supported by overhead mast arms, or hung overhead by span wire attached to poles near the intersection.