Stephen Rees's blog

Thoughts about the relationships between transport and the urban area it serves

Heart and soul of the city | Conservation | Guardian Unlimited Environment

with 4 comments

Heart and soul of the city | Conservation | Guardian Unlimited Environment

The demolition of a vast motorway through the centre of South Korea’s capital and the restoration of a river and park in its place proves that mega-cities can be changed for the better.

I missed this the first time around, so I am grateful to Babara Docherty for posting it to the Livable Region Coalition list.

It’s not often you get post graduate transportation economics in a daily paper but this is really important

Braess’s paradox, named after mathematician Dietrich Braess, gives the lie to governments and local authorities that argue that building more roads reduces congestion.

According to Wikipedia, the online encyclopaedia, it works like this: “For each point of a road network, let there be given the number of cars starting from it, and the destination of the cars. Under these conditions, one wishes to estimate the distribution of traffic flow. Whether one street is preferable to another depends not only on the quality of the road but also on the density of the flow. If every driver takes the path that looks most favourable to him, the resultant running times need not be minimal. Furthermore, it is indicated by an example that an extension of the road network may cause a redistribution of the traffic that results in longer individual running times.”

The article talks about a number of other Asian cities that have done this, but we should all be familiar with the removal of inner city freeways in Toronto and San Francisco which had precisely this effect. This is not just theory – there are many examples that have been extensively reported – so many in fact that Phil Goodwin and others produced a study of studies.

This by the way is not new. Here is a citation which Braess himself gives

J.G. Wardrop, Some theoretical aspects of road traffic Research in Proc. of the Inst. of Civil Engineers, Part II, 325-378 (1952)

So we have known for over fifty years that building new roads generates traffic and taking roads out of the network does not increase congestion it actually reduces it. But somehow that message has still to get through to the BC Ministry of covering the world’s best place in concrete.

Written by Stephen Rees

November 20, 2006 at 5:34 pm

4 Responses

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  1. I think there’s probably a difference between inner-city freeways where there are alternate routes available to take the “distribution of traffic” and bridge crossings that provide the only route.

    For example, you can see the theory at work with the absence of traffic problems surrounding the Canada Line construction. Since there are many alternate routes available, there hasn’t been the chaos that some predicted. Similarly, drivers could probably adapt to the demolition of any one of the closely-spaced Burrard Bridge, Granville Bridge or Cambie Bridge, but I don’t think that demolishing a lifeline route would have the same result.

    Ron

    November 21, 2006 at 3:35 pm

  2. This is a blog about urban transportation. “Lifeline route” applies in rural BC, but there are few places in the lower mainland that would count. Except perhaps the Canoe Pass bridge – the only way to get on or off Westham Island.

    Stephen Rees

    November 21, 2006 at 7:45 pm

  3. I think it’s a question of degree – i.e. the extent to which the network can absorb or support traffic in the absence (whether demolition in the case of Seoul or the Embarcadero or being unbuilt).
    Within the scope of urban transportation, in the case of the Port Mann Bridge, that would then relate to whether that area is “urban” or “suburban”. If it is “urban”, then I suppose the argument could be made that it is entitled to be built-up to the same degree as other urban areas so as to provide the same amenities found in the City.

    Ron

    November 22, 2006 at 3:33 pm

  4. You are entitled to your opinion, but it is not what the research shows. Traffic expands and contracts to fit the space available. Most civil engineers treat traffic as though it behaves like water. In reality it is more like a gas. That is because very little traffic is people just going for a ride. Most trips are to achieve some other purpose. And there are nearly always alternative ways of satisfying that need. For example in the short term you have to make the journey to work, but in the longer term if it gets too frustrating, you could either change jobs, move house or work from home and telecommute. Many trips could have alternate destinations, and in urban areas there are many different possible routes and even mode choices in some cases. And there is also the choice of changing the time of day or day of travel. In over 60 case studies reported from around the world, a road closure resulted in an average overall reduction of traffic in the area of 25%. (That’s the Goodwin study of studies cited in my original article).

    Stephen Rees

    November 22, 2006 at 5:30 pm


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