Between July 2004 and February 2006, research was continued on the safety implications of flush medians in Auckland, New Zealand. A site-by-site benefit/cost analysis found that 38 per cent of studied sites achieved a negative benefit/cost ratio, proving that separate analysis is required for every proposed flush median site. The width of a flush median was found to have no effect on overall benefit/cost ratios. Crash types that increased as a result of installing a flush median were investigated. JA, FD and LB-type crashes are the crash types that were shown to increase as a result of installing a flush median. It was concluded that JA-type crashes increased because installing a flush median reduces visibility. To mitigate the expected increase in crashes that a flush median is likely to cause, visibility from side roads should be improved. It was concluded that FD and LB-type crashes increased as a result of more congestion, which caused longer queue lengths and longer peak periods. The probable increase in FD and LB-type crashes when a flush median is installed can be minimised by ensuring adequate capacity at all intersections along the route. A methodology was formed to predict crash patterns at proposed flush median sites. The Preliminary Guidelines for Safer Flush Medians were updated to include findings from this research. (Author/publisher)
Abstract