Justification for raising speed limit on motorway is ‘nonsense’

Claims increasing the Southern Motorway’s speed limit to 110km/h will boost economic productivity have been rubbished by experts.
On Tuesday, NZ Transport Agency/Waka Kotahi starts consulting the public on a proposal to raise the speed limit on a 17.7km stretch of motorway between Christchurch and Rolleston.
In a statement welcoming the move last week, Transport Minister Simeon Brown said: “Boosting economic growth and productivity is a key part of the Government’s plan to rebuild the economy. This proposal supports that outcome by reducing travel times and increasing efficiency on this key South Island freight route.”
Transport expert Simon Kingham, a geography professor at University of Canterbury, says: “For multiple reasons, it’s just nonsense.”
He adds: “It will have a negligible impact, and the disbenefits will far outweigh any benefits.”
(Expanding the economy was also used to justify Monday’s announcement of halving walking and cycling funding in the country’s projected $33 billion of transport spending over the next three years.)
In a peek behind the curtain of transport planning, Kingham – who, until May, was chief science adviser at the Ministry of Transport – says benefit-cost ratios use estimated time savings, multiplied by the number of vehicles on a road, to come up with a “big number”. This number is mythical time savings, he says, which is then wrongly equated with extra productivity.
We asked Brown for advice he’d received that raising the speed would provide an economic boost. He said: “Around 38,000 vehicles use this corridor daily, and increasing speeds to 110km/h will save a collective 538 hours of travel time every day.” On average, that’s a time saving for each vehicle of about 51 seconds.
Just because there’s a higher speed limit doesn’t mean vehicles will travel that speed along the entire stretch, Kingham says, because traffic doesn’t flow consistently. And even if people arrive at their destination earlier, most don’t do anything productive with that extra time. They’ll probably spend a bit longer scrolling on their phones, he says.
Traffic researcher Dr Glen Koorey, a director of Ōtautahi/Christchurch transport consultancy Via Strada, says raising speed limits on the Southern Motorway might lead to a slight gain in travel time, in theory. “In the real world, you get to the end, and run into Brougham St, and you’re back to crawling again.”
(At the same time it is proposing to let people drive faster along the motorway, the Government has halted a $90 million safety upgrade on Brougham St.)
Kingham, of University of Canterbury, concedes some businesses using light vehicles to ply the route – a mix of state highways 1 and 76 – might get some useful time savings on a faster-flowing Southern Motorway, in the order of minutes. A small number might even be able to get to the end of a journey without having to take a legal break.
However, vehicles travelling at 110km/h, as opposed to 100km/h, use more fuel, so there’s an added cost. (Via Strada’s Koorey says such an increase could add 3-4 percent to vehicle operating costs.)
Is the time benefit of more value than the added cost of extra fuel? “Probably not,” Kingham says.
Higher fuel use also means increased greenhouse gas emissions. Building motorways between cities and satellite towns encourages people to live further away, Kingham says, which induces demand.
Then there’s safety.
Koorey says the number of crashes may well reduce on well-engineered roads.
“It’s what happens when those crashes do happen; they still end up being more severe,” Koorey says. “There’s pretty good evidence about what happens when people go faster. Certainly, if it was 10km/h difference at those kinds of speeds, your deaths and serious injuries are often increasing by 30 percent, equivalent.”
Last week, in Auckland, a truck crashed through a rope-wire median barrier after blowing a tyre, plunging into oncoming traffic and killing three people.  
John Skevington, Automobile Association’s Canterbury/West Coast District Council chairperson, says: “Unfortunately, no speed limit can eliminate all risks on the road, but we do know that new roads built to a standard designed for modern traffic conditions significantly reduce the likelihood of serious and fatal crashes.” 
A recent AA Research Foundation study found there was a 37 percent reduction in deaths and serious injuries at seven newly built roads and bypasses – for crashes on both the new and old roads combined, compared to when there was just one road before.
The AA supports lifting the speed limit on the Southern Motorway. Skevington says the road is capable of safely accommodating the proposed limit, especially considering pedestrians and cyclists aren’t permitted to use it.
The higher speed limit would have an economic advantage, Skevington claims, as it’s “an important economic corridor with tonnes of freight moving in and out of region being carried on it every day”. 
However, there’s no proposed change to the 90km/h limit for heavy vehicles.
Transporting NZ/Ia Ara Aotearoa interim chief executive Dom Kalasih says his organisation supports higher speeds on the Southern Motorway, given the road’s design and safety features. He agrees any time savings would be offset by higher fuel costs.
“The biggest benefit for the trucking sector is light vehicles can complete their manoeuvres more quickly, and so that just helps that whole car driver/truck driver relationship.”
Kalasih says Transporting NZ has recently consulted its members on their views of the road user rules that limits the speed for heavy vehicles to 90km/h.
So, would Kalasih’s organisation support increased speed limits for heavy vehicles on well-engineered roads like the Southern Motorway? “We’re going to wait and have that policy work done.”
Brown, the Transport Minister, tells Newsroom: “New Zealanders utterly rejected the previous government’s plans to slow Kiwis and the economy down with their speed limit reductions. We are going in the opposite direction.”
But if there’s no evidence of economic benefits, as Brown claimed, what’s behind the move?
Koorey, of Via Strada, thinks he knows. “It’s a populist move. A lot of people do want to go faster – I get that.
“If you reduce speed limits – and obviously we saw a fair bit of that in the last few years, with urban and rural speeds going down – people feel like they’re losing something. They feel like I can’t go as fast, I’m losing what they might think is minutes but often is literally seconds.
“You can understand going the other way, for a lot of people that sounds like a good deal, but it’s all those unintended consequences that haven’t always been thought through.”
Submissions on the speed limit change close on October 1.