ViaStrada were commissioned by Tauranga CC to assess the effectiveness of the 30 km/h zone in Mount Maunganui, in terms of vehicle speeds and crashes, taking into account the changes in traffic volumes that have also occurred since its introduction in August 2011. A control zone immediately south of the study area, where the 50 km/h speed limit remained unchanged, was used as a basis for comparing general changes in the area. Five years of speed, volume, and crash data before and after implementation were used to analyse the effects.
The analysis found that:
- Traffic volumes increased in the 30km/h zone by +6%, compared with a decrease in the adjacent control zone (-12%).
- Traffic speeds showed no notable change in the two years immediately before/after the change; however, there was an ongoing downward trend in mean and observed speeds over a 5-year time frame of about -7%, and mean speeds were already below 30 kmh.
- The expected number of crashes in the 30 km/h zone (based on the change in traffic volumes) fell by 21% in the 5 years before/after, compared with a 1% drop in the control zone. However, this finding is not (yet) statistically significant.
It appears that implementing the 30 km/h speed zone has had a positive effect on traffic safety, despite traffic volumes increasing slightly, and contrary to the trends displayed in the neighbouring control area.