Speed is a major contributing factor in fatal and serious crashes in the rural environment (35% of fatal and 28% of serious crashes in 2003). In such crashes, drivers are generally described as travelling too fast for the conditions. Based on the premise that drivers do not deliberately travel too fast for conditions, what aspects of the road alignment affect drivers’ speed choices?
Using highway geometry, speed and crash data collected during 2005–2006 on six 20 km road sections located in Canterbury (SH73), Blenheim (SH1), Wanganui (SH3) and Whangerei (SH1), this research investigates the relationship between curve radii, the preceding speed environment and drivers’ observed curve negotiation speeds. The observed free speeds are compared to the ‘safe’ speed, measured as a function of the design speed of each curve; the relationship between speed and crash occurrence is examined by relating crashes to the difference between observed and ‘safe’ speed.