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Speaker: Sponsored post: Speed and Safety

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  • tussock,

    On the discussion of how speed works, there was an Experiment in Victoria, Oz when I was kid there (early 80's), where they figured a lot of people were crashing on the main freeway north of Melbourne (Hume Highway) because the road was too bloody easy to drive on (design was to allow safe travel at 160k) and put people to sleep.

    So they raised the limit to 120k, from 100. After a year, they had less accidents, less injuries of all types, about the same serious injuries, and a few more deaths. About as expected. They did the math on social costs, and the extra deaths lost significantly: adults are just too valuable.

    NZ roads just aren't that good. At all. I'd point out how much better off society would be if the speed limit was lowered (crash rates and injury rates drop on anything but the easiest roads), but it'd be an easy way to lose an election for any party proposing it, so it's not going to happen.

    Having said that, many local back roads are down to 80k now. Because the council asked and no one objected.

    Since Nov 2006 • 607 posts Report Reply

  • Chris Waugh, in reply to tussock,

    So they raised the limit to 120k, from 100. After a year, they had less accidents, less injuries of all types, about the same serious injuries, and a few more deaths.

    So.... people generally drove more safely and had fewer problems, but when things did go wrong they went much more spectacularly wrong?

    Wellington • Since Jan 2007 • 2401 posts Report Reply

  • BenWilson, in reply to tussock,

    but it’d be an easy way to lose an election for any party proposing it, so it’s not going to happen.

    I don't know about that. A lot of people want speed limits dropped, at least in their area.

    Having said that, many local back roads are down to 80k now. Because the council asked and no one objected.

    Which is the sensible way for it to happen. Each speed limit has to be weighed up on it's merits, so it's not really a national government issue. On a really, really good road, a speed over 100km/h could be justified. We just don't have any roads like that. But if we did, I wouldn't want a law made prior to the road being created to block it.

    Nationwide efforts need to be caveated to conditions. The law dropping maximum speeds to 40 around schools was a good idea. But even still, it's nowhere near sufficient. Traffic engineers should judge each case individually. The pedestrian traffic on Ponsonby Rd is sufficiently large that making it 40km/h was a good call, despite there being no schools anywhere along it.

    Auckland • Since Nov 2006 • 10633 posts Report Reply

  • Matthew Poole, in reply to BenWilson,

    On a really, really good road, a speed over 100km/h could be justified. We just don’t have any roads like that.

    Bollocks we don’t. The new motorways constructed in Auckland with hard dividers are equal in standard to any high-speed roadway in the world. Pretty much all the Auckland motorway network, in fact, is of a build quality that posted limits > 100km/h would be safe. The CMJ is built to a standard that could support a higher limit, but it’s posted at 80km/h because of the volume of merging/splitting that occurs through that section.

    What we don’t have are country roads that are safe at their posted 100km/h limit. Many are barely safe at 80km/h, never mind anything higher. Big stretches of SH1 fall into that category.

    Nationwide efforts need to be caveated to conditions. The law dropping maximum speeds to 40 around schools was a good idea. But even still, it’s nowhere near sufficient. Traffic engineers should judge each case individually.

    An ordinary suburban limit of 50km/h increases pedestrian fatalities significantly. Between 40km/h and 50km/h is where the survivability of a collision drops dramatically. It’s the difference between the majority of hit pedestrians surviving and the majority dying. If the limit for suburban side streets were even lower, say 30km/h, most car vs pedestrian collisions would be survivable except for very unfortunate combinations of events.

    Auckland • Since Mar 2007 • 4097 posts Report Reply

  • Rich of Observationz,

    Matthew is right - SH1 south of Drury and north of Albany are as low-risk as any road globally. (The wide medians on the former are, I think, safer in an accident than a physical barrier). I'd also argue that a lot of rural roads have a low risk of two-party accidents because of the very low traffic volume.

    Back in Wellington • Since Nov 2006 • 5550 posts Report Reply

  • Matthew Poole, in reply to Rich of Observationz,

    The wide medians on the former are, I think, safer in an accident than a physical barrier

    Hard dividers are used on the Autobahn, that most iconic of high-speed roads. They have buffer space between some installations, but that's more to allow for deflection I suspect since the barriers are often substantial. We could certainly handle a 110-120km/h limit on all of Auckland's motorways (CMJ excepted, per above) without any real issues other than the incapability of drivers to handle the complexities of joining and merging with the traffic flow.

    Auckland • Since Mar 2007 • 4097 posts Report Reply

  • BenWilson, in reply to Matthew Poole,

    The new motorways constructed in Auckland with hard dividers are equal in standard to any high-speed roadway in the world.

    That's a pretty big call. There are definitely some high quality stretches of motorway, but I was pretty much talking about highways. Why bother with super high speed motorways? If you're going 100km/h then the times people take to get around just aren't going to be significantly improved by adding 20km/h, when the entire city is less than an hour from one side to the other, and only a small proportion of that trip will generally be actually at the speed limit, given traffic.

    On the highways, as you agree, we don't really have much where a really high speed is justified, and for the most part the opposite is true, it would be better if the speed limit were lower.

    If the limit for suburban side streets were even lower, say 30km/h

    The way they seem to be bringing that about is by speed humps, but they might as well change the limit if that is the whole intention.

    SH1 south of Drury and north of Albany are as low-risk as any road globally

    I guess those are technically motorways. I wouldn't class them as autobahn good, though. They're way narrower and bendier, and they seem to undulate more. I doubt I'd feel safe at 240km/h even if there were no other cars on the road.

    It’s the difference between the majority of hit pedestrians surviving and the majority dying.

    That's certainly a nice break-even point, but the way we rate death proportions vs right to speed doesn't seem to follow any clear logic, at least not at a political level (I expect engineers have a different view). It's not really enough to just classify the chance of death from each collision. You also have to consider the chance of the collision, and that's got a lot of factors, but a big one is pedestrian density. That's extremely variable around the city, so each street really should be weighed up on its own merits.

    Auckland • Since Nov 2006 • 10633 posts Report Reply

  • Brent Jackson,

    New research from The University of Western Australia has found strictly enforced speed limits could have a detrimental impact on road safety.

    Auckland • Since Nov 2006 • 614 posts Report Reply

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