Fiddling with highway speed limits: A small step in the wrong direction

Spain reduces highway speed limit to 110 km/h to decrease oil dependency. Meanwhile, the Netherlands starts a pilot to increase speed limit to 130 km/h on some highways. What’s going on?

The Afsluitsdijk where drivers are now allowed to consume a bit more oil (photo: TobyA)

The Afsluitsdijk where drivers are now allowed to consume a bit more oil (photo: TobyA)

Briefly, nothing. A small 10 km/h change over 100 km/h will not make a big difference either to decrease oil consumption in case of Spain, nor on the Dutch highways — especially if the new limit will be coupled with tighter speed camera tolerances, which leaves you with pretty much the same de facto speed limit as today (I would say 135 km/h). But it does send a political message.

To look back a bit, note that highway speed limits range from 100 km/h (Norway) to 140 km/h (Poland) in Europe, as well as the infamous unlimited speeds on (parts of) the German Autobahnnen. This latter one-country exception provides the car industry with the excuse to sell cars all around the world which are carefully designed for breaking the law everywhere except certain German highway segments.

These differences, luckily, force us to stop searching for “best practices” (although an argument in the Netherlands was that “abroad” the limit is already 130 km/h — this fictional country named Abroad always intrigued me) and really think about what could be an optimal speed limit on the highway.

Capacity and consumption/emissions characteristics guide us to an optimal speed of about 80-90 km/h, above which the capacity is reduced and emissions per traveled km increase again. Traffic safety of course monotonously decreases by speed, and in fact the difference is also significant in this speed range: the Dutch Institute for Road Safety Research (SWOV) calculated that at the current speed of 120 km/h, a speed increase of 1 km/h (not 10 km/h) already means a 3,3 % increase in deaths.

On the other hand, the pleasure of speeding is hard to quantify, but travel time isn’t: in case of the Afsluitdijk, where the new speed limit is introduced, a time saving of only 1 minute and 10 seconds is possible over the 30 km length.

In short, although a general maximal road speed limit of 80 km/h does not seem to be politically feasible, any further increase above this range is also scientifically not justifiable — it is nothing else than a cheap way to please some voters. Surprise: there are elections today.

Update: just like most scientists, the “most senior traffic offence official” is also against the speed limit raise.

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3 Responses to Fiddling with highway speed limits: A small step in the wrong direction

  1. Unusually, this is an area where the UK and the Netherlands are doing the same thing. My ex boss asks whether road fatalities will now rise.

    • Well, although the situation is still great here, the direction of current government policies is pretty much pro-road, anti-public transport — at least there seems to be a cross-party agreement on cycling.

      In this case, isn’t it great that decisions take soo much time in the Netherlands :)
      (this 130 was a topic already just after the elections, if I remember correctly. Also, maybe today’s election can stop cost-cutting in public transport.)

  2. In 1973, the US enacted a 55MPH (88.5km/h) speed limit.

    http://en.wikipedia.org/wiki/National_Maximum_Speed_Law

    The law was repealed in 1995 by Freedom-loving Republicans.

    There does seem to be an inverse correlation between oil price and the speed limit which the public will tolerate.

    -danny