Peter Calder: Sharp eyes study speed limits

Frank Louie aims at traffic on Hillsborough Rd. Photo / Greg Bowker

The traditional 50km/h restriction on suburban roads may be replaced by lower - and higher - speed limits.

Just 14 seconds after Constable Frank Louie pulls the speed-gun trigger, the high-pitched squeal announces that it's locked on to a target.

He has clocked the late-model Mazda at 78km/h, and it doesn't slow down as it passes. Maybe the driver doesn't have time to react at that speed to the uniformed figure in a high-vis vest who steps out on to the road and points at him; maybe he thinks he can ignore him. Louie studies the rego number. The ticket - $230 plus 35 demerit points - will have been delivered by now.

Louie, who's based at the strategic traffic unit at Balmoral, is partial to this spot, on the corner of Hillsborough Rd and Goodall St, at the northern corner of the Hillsborough Cemetery. "You always get plenty of speeders there," he says, in a matter-of-fact tone, noticeably free of either regret or relish.

It's a high-speed zone because many drivers have just exited the Southwestern Motorway and failed to adjust their speed to suburban levels. And it's a good hunting ground because a slight kink in the main road about 100m north means drivers can't spot him until it's too late.

In the 20 minutes or so we're there, Louie nabs three more: one, who rather foolishly professes not to know the prevailing speed limit, gets a $120 ticket and 20 demerits; two others, more apologetic, get off with written warnings. "It's not the crime of the century," he says, his voice more reassuring than reproving. "But you really must keep an eye on that speedo, eh?"

I have come to watch Louie at work because Hamilton City Council is considering ditching the 50km/h speed limit in favour of a 40km/h limit in residential areas and 60km/h or even 80km/h on arterial roads.

Louie can see some merit in the plan, but he makes it plain that, no matter how wide its four-lane expanse may seem, Hillsborough Rd is residential. He points out the kids, just out of school, dawdling along the footpath and negotiating gaps in the traffic to cross the road; the front yards only metres from traffic lanes; the domestic driveways that give straight on to the street.

It's not a police decision, he explains - councils set speed limits; police just enforce them: "I do support the idea [of differential limits] but depending on the area. I just don't think it would be prudent to increase the speed limit along here. It's just too quick, eh."

In truth, the part of the council plan that calls for increasing speed limits is less likely to get the official go-ahead than the part that calls for dropping them. The death of landscape designer Nicole Mace and the serious injury of photographer Jane Ussher, both in 2005 on Ponsonby Rd, resulted - after four years of official chin-scratching - in the imposition of a 40km/h limit on that busy stretch of street.

It's a restriction honoured as much in the breach as the observance in my recent experience - maybe Louie should set up there for a day - but it certainly had an immediate and salutary calming effect. It doesn't feel as though you're taking your life in your hands when you cross the road these days.

What I didn't understand was why Ponsonby Rd should be singled out for special treatment. Any suburban shopping strip, where cars exit streetside parking spots and parents push buggies, has to be just as dangerous.

Simple maths shows that stopping time increases exponentially with speed: not counting reaction time, it takes 24m to stop if you slam the anchors on at 38km/h; increase the speed by 50 per cent to 58km/h and the stopping distance almost doubles to 43m. Between 30km/h and 50km/h the chance of a pedestrian dying in what police call "car vs pedestrian" increases from 10 per cent to 80 per cent.

In practice, traffic congestion commonly keeps speeds down below 50km/h, but the fact that cars may travel at 50km/h (which in practice means 58km/h) is surely worth official attention.

Fortunately it is getting some. Andrew Bell, the regional road safety adviser for Auckland Transport, says the Hamilton proposal is part of a national "safer speeds" pilot strategy. In Auckland, they are studying lower speed limits on problematic stretches of two-lane rural road.

Bell says that, with 20km/h shared spaces, 30km/h on Queen St and 40km/h school zones Auckland has certainly started the process of removing the default 50km/h limit. But there's a long way to go yet. Just ask Frank Louie.