Many people will have seen a recent proposal by Auckland Transport (AT) to reduce speed limits across Auckland, including a 30km/h blanket speed limit in the CBD, and will be asking "Why?"
Firstly, bringing down speeds on our highest-risk roads is something we should all support. New Zealand's road toll has been going the wrong way at an alarming rate, and Auckland has had a particularly big increase in deaths and serious injuries.
So action is needed and reducing speeds can be an effective, efficient and affordable option, when done well.
Many roads in the Auckland CBD are in the highest-risk 10 per cent of the Auckland network, as defined by the Speed Management Guide (the official framework for setting speed limits nationally). AT is right to target these roads, and the other residential and rural roads in the top 10 per cent.
Secondly, lowering speed limits is rarely popular, whether it's in Auckland, elsewhere in New Zealand, or overseas.
If authorities want the social licence to make these changes, they need to demonstrate a strong evidence base, and ensure what they're proposing makes sense to the public. And this is where the AA thinks AT is falling short.
The Speed Management Guide recommends 40km/h as the safe and appropriate speed for most roads in the CBD, not 30km/h limits as AT is suggesting.
Cities like Melbourne and Sydney have introduced 40km/h limits in their CBDs and have seen substantial crash reductions. Closer to home, a 40km/h limit has worked well on Ponsonby Rd.
So the AA will call for the new limit in the CBD to be 40km/h, not 30km/h.
But on the big arterials like Hobson, Nelson and Fanshawe Sts, we would question whether speed limit reductions are practical. Research has shown that if a speed limit doesn't suit the physical environment then rates of compliance will be low. Telling someone to drive at low speeds on an extremely wide, multi-lane road in free-flowing traffic is likely to be an exercise in futility - particularly if the new limit is 30km/h.
The only likely way to get compliance would be relentless enforcement, a sure-fire recipe for public resentment. On Nelson St in particular, there are also concerns that a lower speed limit would push too much traffic back on to heavily congested motorways.
So before looking at lowering the speed limit on these roads, we think AT needs to look at what engineering work needs to be done to improve them so they're safer for everyone at current speeds. That could mean anything from pedestrian over-passes and under-passes to better designing the phasing on pedestrian crossings to discourage jay-walking.
Most of the 700km of roads where speed limit changes are proposed are in rural areas (Franklin and Rodney), and six town centres are set to drop to 30km/h.
We think AT needs to be guided more closely by the evidence, and by what will make sense to people. On many of the 100km/h rural roads earmarked, the Speed Management Guide recommends 80km/h but AT is proposing 60km/h.
Of 14,000 responses in a survey of Auckland AA members, 62 per cent opposed or strongly opposed a blanket 30km/h speed limit in the CBD, while only 16 per cent were in favour. There was similar division about what's being proposed in town centres and rural areas.
Asked about he speed limit on Nelson St, less than 2.5 per cent said 30km/h, while nearly 90 per cent said 50km/h or more.
This is an issue where public support is critical, resulting in low compliance, high public frustration, and a future situation where speed limit changes become a no-go zone politically. That would be a poor outcome for road safety.
• Barney Irvine is principal adviser, infrastructure and motoring affairs, for the Automobile Association.