18 mph Speed Limit: European? Sensible? Read On.

In two consecutive issues of the estimable Southwest Cycling News (print) publication, I have seen the picture below.

18 mph Albuquerque sign

Editor Fred Meredith shot the photo of the sign on a bicycle boulevard — a low-traffic, residential street configured as a through route for bicyclists — in Albuquerque, New Mexico while attending the 2010 League of American Bicyclists National Rally. Meredith wears more than one bicycle helmet — he also works under contract for the League’s education program, so it is natural for him to attend the National Rally.

Now, please don’t get me wrong, I’m an instructor in the League’s program, and I’m also a proponent of bicycle boulevards and of low speed limits on residential streets. Many European residential streets have a similar speed limit. and so do some streets in Montréal, Québec, in Canada — as per the sign on the left in the photo below.

Some signs in Montréal, Québec

Some signs in Montréal, Québec

Similar speed limit, what? That sign reads 30!

Yes, it does: 30 kilometers per hour. Canada changed its speed limit signs from miles to kilometers in 1977, conforming to the rest of the world, the only major holdout nations being the USA and the United Kingdom. Part of Canada is French-speaking, the kilometer is a French invention, and that might have something to do with Canada’s divergence from its southern neighbor.

So, anyway, American bicycling advocates on pilgrimages to Europe see the 30 km/hour signs, which look like a good idea to them, and decide to transplant the idea back home.

As I said, I support lower speed limits. I have a few problems with the sign, though.

First of all, our bicycling advocates appear to be math-challenged — or perhaps they want to go a bit lower on speed limits than the Europeans.

30 km per hour converts to 18.64 miles per hour, rounded to the nearest 1/100th. Rounded to the nearest whole number, then, it’s 19 miles per hour — not 18.

There’s another problem with the number 18 — or for that matter, 19. Have you ever before seen a speed limit in miles per hour with a final digit other than zero or 5 — or in kilometers, with anything other than zero? No, you haven’t. There are a couple of reasons. The steps in speed limits need to be large enough to be meaningful. Also, a zero and a 5 look so different that they are very unlikely to be confused with each other at a glance, or if a sign is damaged or partially obscured. An 8, on the other hand, is easily confused with a 3, or a zero. A 9 is easily confused with a 2 or a 7.

The requirement that speed limits go by jumps of 5 or 10 is written into US standards documents. The US standard, the Manual on Uniform Traffic Control Devices, section 2B.13, includes the following wording:

The speed limits displayed shall be in multiples of 5 mph.

Am I nitpicking by raising these issues? I don’t think so. Confusion makes a speed limit harder to observe, and harder to enforce. So do speeds which must be estimated, between the markings on a speedometer. Failure to observe standards exposes governments to liability risks. A nonstandard speed limit can give speeders and their lawyers a legal loophole.

The issue is similar to the one with bike lane color that I described in an earlier post.

The usual school-zone speed limit in the USA is 20 mph. It is only slightly higher than the European and Canadian 30 km/hour speed limit, and it conforms to US standards. This same 20 mph speed limit is already being used in residential neighborhoods in the USA. If 20 mph is too high, 15 also is possible, and I have seen it, in parking lots and the loading/unloading areas of airport terminals.

Advocates of an 18 mph speed limit are acting in disregard of existing American standards which would give them very nearly the same speed limit, on a sign that is more readable and immune to legal challenges.

When and if the USA goes over to speed limits in kilometers per hour, the current speed limits will be adjusted up or down slightly so the numbers end in a zero, as in other countries.

If the USA makes the conversion, a large number of “speed limit 30″ signs will become available for re-use as 30 kilometers per hour, and the bicycling and neighborhood safety advocates can expect to have the genuine European speed limit at a bargain price. I will support them in that.

10 Responses to 18 mph Speed Limit: European? Sensible? Read On.

  1. What do you say to the assertion that speed limits have little influence on actual driving speeds, that only the design of the road matters?

    • The assumption that actual speed depends only on road design would require that the type of traffic on the street have no influence. If a street is used heavily by bicyclists, and there isn’t sufficient width for motorists to overtake, they will have to slow to the bicycists’ speed. On a residential street which children use for travel or play, most motorists will drive more slowly out of caution, especially if the street is in their own neighborhood. In any case, a bicycle boulevard is designed with barriers, diverters and neighborhood traffic circles, to slow traffic and to exclude all but local motor traffic, reinforcing these tendencies.

      Then there is traffic law enforcement. The assumption that only street design affects motorists’ speed requires that enforcement and penalties be very lax or nonexistent. That is the unfortunate situation in much of the USA, but it is an adaptive response to a bad situation. It is like assuming that the rate of convenience-store robberies depends only on how secure the cash register is, and has nothing to do with whether criminals are arrested and punished.

  2. While you both are normally correct that such signs are silly (though you both state different reasons why), a really peculiar sign such as that above garners a lot of attention from motorists and law enforcement alike – as long as they are very rare. As would the arret sign if it were transplanted into New Mexico. It is the same phenomena that appear to make green paint work when it is first tried.

  3. Make it 15, or even 20, that doesn’t matter to me if you really think the number is an issue.

    And don’t call reducing the speed limit a bicycle issue. This is a human life issue, and the primary benefactors are pedestrians. I favor reducing the speed limit on all roads in urban areas with regular pedestrian traffic.

    Design and enforcement are both important considerations, and both need to be be improved. Roads can and should be built to inhibit fast driving. Fines can and should be raised to discourage this deadly behavior.

  4. I wonder whether the 18 mph sign would be ignored as a joke since it would be so unusual.

    Along the lines of Eli’s comment, lowering the limit without other adjustments to the road would slow down some drivers; although I suspect that these drivers are already fairly conscientious such that risk to peds and cyclists would be minimally affected. I do think that it would have a positive effect on driver reaction to cyclists when they are taking the lane.

  5. My problem with bicycle speed limits is enforcement. No jurisdiction that I know of requires bicycles to have a speed measuring device so the bicycle rider cannot know his actual speed. Where I live, bicycle speed limits can be enforced and often are (radar) on multi-use bicycle pathways, usually on Saturdays, when there are pedestrians, skaters, dog-walkers, strollers and anyone else who ventures out. I would rather see cautionary speed signs – yellow – where excess speed could be dangerous to the bicycle rider.

    • Ah, your comment raises another issue here! The speed limit is intended for motorists, so that the street will be pleasant and safe for cyclists. On the other hand, some cyclists ride faster than this, and if electrically-assisted bicycles become popular, more will. That is aside from the issue of bicycle boulevards’ also possibly being used by people on gasoline-powered motorized bicycles and mopeds, which are faster yet as well as noisy and polluting.

  6. Take a look at the 20 Is Plenty for Us campaign in the UK to see the reasons for and success they are having with 20 mph speed limits on residential streets there without physical traffic calming.
    http://www.20splentyforus.org.uk/

  7. 20 mph would work just as well in practice but perhaps the unusual number does catch people’s attention. In BombTown, our school zones are posted 15 mph when the lights are flashing.

    Does anyone know if someone has challenged a bike boulevard speeding ticket in Albuquerque on the basis that the speed limit and signage does not conform to the MUTCD?

    But to split hairs: “The speed limits displayed shall be in multiples of 5 mph.” 18 = 5 * 3.6

    Guess they should say “whole” multiples…

  8. @khal spencer

    I saw lots of 20 mph signs in residential areas in Phoenix, Arizona during my recent visit. So, I can say that the Southwest hasn’t been entirely weaned away from US standards.

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