Lower limits reduce pollution
Lowering speed limits doesn’t just save lives, it can also help to reduce emissions, says Waka Kotahi.
As part of the outgoing government’s Road To Zero safety campaign, the transport agency estimates it has lowered limits from 100kph to 80kph on around four per cent of New Zealand’s highways.
Experts say someone’s chances of surviving a head-on car collision rapidly increase when vehicles are being driven at 80kph or lower, while lower speeds have also reduced emissions.
Waka Kotahi modelling shows the optimum speed for light vehicles travelling on our roads is 70-75kph – and anything above that increases the car’s emissions impact.
“The faster you go, the more the fuel is used to drive the car,” says Ralph Sims, emeritus professor of sustainable energy and climate mitigation at Massey University.
He has been studying Waka Kotahi documents that show the potential emissions increase from making the whole Waikato expressway 110kph would come in at about five per cent over the next few years even accounting for more electric vehicles being in the fleet.
For any roads shifted from 80kph to 100kph, the transport agency’s model predicts an average increase of between five and 10 per cent in emissions.
This is calculated using the vehicle-emissions prediction model developed by Waka Kotahi and Auckland Council several years ago. It predicts pollution from vehicles in our fleet under typical road, traffic and operating conditions.
Len Gillman, an expert in conservation biogeography, says these results aren’t unique to New Zealand. “The OECD has done work which shows a reduction from 110 to 90kph reduces emissions by 23 per cent. It makes a huge difference how fast you go.”
Despite these benefits, speed-limit changes have frustrated many drivers and the incoming government has been vocal in its criticism.
Simeon Brown, pictured, National’s transport spokesman, says Waka Kotahi will be asked to review the recent speed-limit decisions.
“They will have to take into account the benefit-cost analysis, which looks at the impacts on travel times,” he told RNZ in September. Brown has expressed particular concern for the economic impacts of prolonged travel times.
Gillman, however, says the difference is actually very small. “Dropping the maximum speed by 10kph only makes two to four minutes difference over 100km. It’s only minimal – enough time to get in the queue for a coffee, but that’s all.”
Sims believes the sacrifice is worth it. “Transport emissions are about 19 per cent of our total greenhouse gas emissions and most of that’s road transport. A typical family car in one year would produce around three tons of carbon dioxide. That’s a significant footprint, equivalent of flying from Auckland to the UK.”
He adds any move by the incoming government to reinstate faster speed limits would be a major blow to climate action although he realises lowering speed limits will always be a hard sell to Kiwis. “People in New Zealand love their cars and they love to drive at fast speeds,” he told RNZ.
