What is an Optimal Speed Limit?

Recent New Zealand Government policy has introduced new Setting Speed Limit Rules that aim to increase or reverse many current lower speed limits, with the rationale being to improve economic efficiency. However, recent research and policy advice would suggest that, in many cases, a lower speed limit will be the more “optimal” one to choose. 

A review of State Highway speed limits found that optimum limits for most highways were <80km/h. And a recent economic assessment of several rural speed reduction options in Tasman District produced Benefit/Cost Ratios above 5:1. For urban areas, the benefits are less clear; however, there are likely to be other benefits there that are more difficult to accurately quantify, including health benefits from active mode shift, improved amenity, and reductions in air pollution and noise. 

This presentation summarises these investigations and offers some considerations for Road Controlling Authorities reviewing their own speed management networks