speed-limit-injuries-cars_jpg_662x0_q100_crop-scaleThere has been some great discussion lately on this blog about lowering speed limits. An example was given of the Albert Road/Victoria Road (Devonport) corridor after the roundabout with Lake Road. Apparently, there was a proposal to reduce the speed limit to 30km/h and this was opposed by the Police. I am not sure what NZTA/AT had to say.

It seems like such a no brainer as that route is a dead end and lowering the speed limit would help increase visitors by making it more pedestrian and cyclist friendly. Really what is needed is a shared space like in Fort Street. As with Fort Street, this would be a boon to the struggling local businesses and would fit in with the current remodelling of the area in front of the Devonport ferry building. In addition, the difference between driving that 1km distance at 50km/h and 30km/h is around 10 seconds.

Chase Scene
A cyclist on a typical auto centric Auckland street – a complete lack of subjective safety

This article debates what the speed limit should be within cities and points out the exponential risk to all road users, but especially pedestrians and cyclists, from higher speed limits. Speed limits are normally set by using the 85th percentile rule (a rule based on cutting edge research – from 1964), which means that the speed limit should reflect the speed that 85% of motorists drive under. No account is taken of whether that speed is appropriate for the area or if it creates a safe atmosphere for the child wanting to cycle to school or the elderly lady cycling down to get a loaf of bread.

There doesn’t just need to be some tinkering around the edges on the design of our streets. There needs to be a paradigm shift on how we think about streets and who they are used by. We must remove cars from the top of our transport hierarchy and put people back.

Separated cycle track - not pretty
Separation doesn’t have to be pretty or gold plated – it just has to protect cyclists

We should start by assuming that the speed limit on all streets within the city should be 30km/h. A case must then be made for the speed limit being higher. That higher limit can only be instigated once pedestrians and cyclists are safely separated from the motor traffic. Simple and yet so difficult.

Aren’t cities about people?

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18 responses to “Lowering speed limits: Cutting the Gordian knot

  1. Here is a great write up on ’85th percentile’ from Copenhagenize. http://www.copenhagenize.com/2012/11/the-85th-percentile-folly.html

    85th percentile was never designed to be used in urban situations. It was for highways but somehow (I can guess why – traffic flow) it was allowed to creep into urban road building standards.

    I was also advised by an AT engineer that the Police don’t like 30 kmh areas as they are ‘too hard to enforce’. My answer was that if the street is designed properly, no enforcement is really needed.

  2. In NZ we don’t (fortunately) rely on an “85th percentile” rule; if anything, we pay attention to the MEAN speed, which is of course lower. Makes sense, because if you shift a speed limit to the existing 85%ile the mean traffic speeds will creep up nearer to this, pushing the 85%ile higher, etc…

    More attention in NZ is paid the adjacent land use and activities (incl. level of walking/cycling) and physical road environment factors, with a “points” system used to determine the appropriate speed limit. It’s not bad in general, but it suffers from a lack of systematic method for determining speed limits below 50km/h – you have to argue these case by case. I highlighted some of the problems with the existing system a couple of years back in a paper – see http://ir.canterbury.ac.nz/handle/10092/6293 if you’re interested. Currently NZTA are reviewing the way speed limits are determined, but it’s slow going.

    1. Maybe in ChCh Glen but I was talking to a very senior AT engineer last week and he was quoting 85th percentile when discussing 30km/h speed limits in residential streets.

      1. It’s got nothing to do with Chch or Auckland; it’s part of the official “Speed Limits NZ” procedure in the Setting of Speed Limits Rule. Table SLNZ3 shows that, for example, the mean speed in a 50k zone should be 50km/h (85%ile of 60k), the mean speed in a 100k zone should be 100km/h, and so on. For speeds <50k the Rule states that MEAN speeds should be within 5km/h of the posted speed limit.

          1. Guidelines for setting speed limits section 2.4..

            “Speed limits of 20, 30 or 40 km/h may be set for local roads or minor collector roads in urban traffic areas where the road is used by motorised traffic and pedestrians or cyclists (eg, shared zones) and a speed limit less than 50 km/h is necessary for safety purposes. Speed limits of 20, 30 or 40 km/h are generally not suitable for roads serving a significant collector or arterial function.

            These limits can only be set if the calculated speed limit for the road is 50 km/h and appropriate and safe traffic engineering techniques are applied to ensure that the mean operating speed of motorised traffic is kept to within 5 km/h of the speed limit.”

            That looks problematic to me. The heart of the problem is right up at the top, in the “Setting of Speed Limits” guidelines. Rule 54001 as it says.

            “2.3(1) The urban speed limit is 50 km/h.”

            “Except when a different speed limit is set under this rule..”

            Wouldn’t it be better if the urban speed limit was 50 km/h.. except for significant collector or arterial roads, or when a different rule is set.. where that is safe etc”

          2. Wouldn’t it be better if the urban speed limit was 30 km/h.. (obviously.. duh!)

          3. Tim, I totally agree; it does nothing to help encourage lower speed limits. As I noted in my paper, it errs on the side of the default (50k/100k) situation; you have to work a lot harder to introduce something like a 30k zone, with very little technical guidance given (something I’m trying to help fill in some of the gaps at present).

          4. The silly thing is the Dutch have been doing this for decades now. It can it be that hard.

        1. Perhaps there’s a disconnect between the law and what the engineer was telling me? Maybe it’s not widely understood?

          1. When discussing 30kmh he didn’t mention mean speeds once. It was all about 85th percentile. This was a senior manager I was talking to.

    2. Yes I hope you are right Glen but I understood that the 85th percentile was still used. Is that part of the review you refer to?

  3. I have commented in the past (although i cant find a link just now) that I suggested a 30kph limit on the parallel cycle friendly routes to the AT rep when attending the Dom Rd progress open day thing. Was told it couldn’t be done without NZTA approval. Actually come to think of it I suggested that a 1km radius be drawn around Kowhai intermediate and 30km limit imposed within there. I would have thought that that kind of close to a school limit would be an easy one to convince people of the merits of. Assuming the requisite paradigm shift has to come about gradually.

    1. They can do it without NZTA approval. It just has to meet the necessary NZTA standards for speed limit setting and then create a bylaw (as I understand it). The will just isn’t there though.

      1. What would it take to create the will? Aside from more deaths?

        I believe I’m not the only person here that drives at 40 or less in residential streets. After a few months of this I must say I’m pleasantly surprised I haven’t met a few impatient drivers by now.

        The problem I have though is the street design is often hopelessly mismatched with the context.. Some streets are obvious, in fact they feel 30-ish as they are. On others 40 feels right. Then there are plenty (residential streets that are not “main roads”) with vast acres of tarseal, unmarked apart from racing lines round the sweeping curves, and literally no pedestrians… so they’re 50.. and that feels slow.

        Some of the Dom Road “cycle” roads would fit my informal “feels like 30-ish is about right here” policy. Can we ask for a trial period?

        1. And I think the way the road “feels” is exactly why it is so hard to get the limit lowered. The Police/NZTA/AT are reluctant to have a speed limit that doesnt reflect the reality of the road – and safety be damned.

          I think we should be looking to narrow roads, remove centre lines and widen footpaths whenever a street is worked on. Even just white lines designating the parking area and removing the centre line, would help to make streets feel narrower and create traffic friction. In that way parked cars can actually help to slow traffic.

          I think both your and Alan’s suggestions above are great and would create much better environments for walking and cycling.

  4. There is lesson to learn from Formula 1 racing. People have short memories and sadly it is all about timing.
    First crash – get rules ready, Second crash (if you’re lucky it’s not a death) – put rule in place
    This is early 2012
    Formula 1’s governing body has rejected a move by teams to lower the pit lane speed limit during races.
    Most teams backed a proposal to lower the limit from 100km/h (62mph) to 60 km/h (37mph) in the interest of safety
    The FIA also considered what the cars would look like travelling down the pits at 60km/h during the race and felt that they would appear too slow.
    This is mid 2013
    In order to reduce the risk of similar accidents in the future,
    2) Article 30.12**, which will provide for a reduction of the pit lane speed limit during races from 100km/h to 80km/h (with the exception of Melbourne, Monaco and Singapore, where due to track configuration the limit remains at 60km/h).

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