Safety performance functions for traffic signals: phasing and geometry

A significant proportion of urban crashes, especially serious and fatal crashes, occur at traffic signals. Many of the black-spots in both Australia and New Zealand cities occur at high volume and/or high speed traffic signals. Given this, crash reduction studies often focus on the major signalised intersections. However, there is limited information that links the phasing configuration, degree of saturation and overall cycle time to crashes. While a number of analysis tools are available for assessing the efficiency of intersections, there are very few tools that can assist engineers in assessing the safety effects of intersection upgrades and new intersections. Safety performance functions have been developed to help quantify the safety impact of various traffic signal phasing configurations and level of intersection congestion at low and high-speed traffic signals in New Zealand and Australia. Data from 238 signalised intersection sites in Auckland, Wellington, Christchurch, Hamilton, Dunedin and Melbourne was used to develop crash prediction models for key crash-causing movements at traffic signals. Different variables (road features) effect each crash type. The models indicate that the safety of intersections can be improved by longer cycle times and longer lost inter-green times, especially all-red time, using fully protected right turns and by extending the length of right turn bays. The exception is at intersections with lots of pedestrians where shorter cycle times are preferred as pedestrian crashes increase with longer wait times. A number of factors have a negative impact on safety including, free left turns, more approach lanes, intersection arms operating near or over capacity in peak periods and higher speed limits.


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Filing Info

  • Accession Number: 01495575
  • Record Type: Publication
  • Source Agency: ARRB
  • Files: ITRD, ATRI
  • Created Date: Oct 17 2013 10:07AM