Research was carried out between 2005 and 2006 to determine if there were benefits or disbenefits associated with sealing unsealed roads, and if so, to determine a procedure for calculating the accident savings (or costs). Road data and seal extension site information were obtained from various district councils in New Zealand and combined with the Ministry of Transport’s accident data to give accident rates before and after sealing.
No statistically significant change in the accident rate was found following the sealing of roads. To determine any regression to the mean effects, a background trend analysis was conducted and found no significant overall change in the accident rate during the period 1990–2005.
The research concludes that there is no statistical benefit or disbenefit associated with sealing unsealed roads and recommends that site specific before and after studies are conducted into the study outliers and a portion of flat South Island sites.