Increasing speed limits defies the science

8 July 2024

Public Health Communication Centre / Lou Wickham

- more deaths and pollution predicted

The government is proposing to increase speed limits. Raising speed limits will lead to increased deaths and serious injuries on our roads. In addition, increasing speed limits is likely to worsen air quality and increase greenhouse gas emissions. The evidence suggests that the benefits of estimated time savings are overstated and don’t always improve economic productivity. The health impacts of raising speed limits are likely to be significant and wide-ranging, and the costs will be far greater than any benefits.

See here for the full briefing from Simon Kingham and Angela Curl which references two Emission Impossible Ltd publications showing:

• Over 2,000 people die each year in NZ from traffic-related air pollution (Kuschel et al., 2022).

• The optimum speed for minimising emissions is 60-80 km/h (Metcalfe J., 2023).

We fully support Oxford Professor Dorling:

If you could do one thing to reduce health inequalities?

Implement 30km/h speed limits where 50km/h ones have usually been in place.

Professor Dorling’s reasons are that it is cheap, easily done, and in addition to reducing deaths and serious injuries, especially among children, it brings wider benefits such as less pollution and stronger communities. It would further reduce inequalities as people tend to be at most risk of being hurt or killed by cars in the poorer parts of towns and cities. 

This conclusion is likely to be equally important in NZ as we know that rates of injury and death on the roads disproportionately affect Māori, younger people, and those in low-income communities. Our own research demonstrates that exposure to traffic-related air pollution is worse for people living in lower income areas.

So why is the Government proposing this?

The case for raising speed limits relates to time savings and enhanced productivity. However time savings are never as big as expected and any benefits are based on the assumption that people use time savings to be more productive, which they often don’t. In fact, making it easier to travel further and faster encourages people to travel longer distances; a concept called induced demand, which creates more traffic problems.

We concur with Professor Kingham and Dr Curl that “the negative health impacts of raising speed limits are likely to be significant and wide ranging, and the costs will be far greater than any benefits”.

Readers are encouraged to consider making a submission on this proposed policy change, which are due by 11 July. Details on the Ministry of Transport’s website.