7 Comments

  1. Kevin McDonald

    All transportation system usage is in some way induced demand–if not, we’d all be trying to get to work on indian paths. The real question is whether the new trips are frivolous (i.e. they do not contribute to better quality of life/ economic growth). Accommodating growing demand through added capacity (Woodrow Wilson Bridge Reconstruction in DC, for example) can be beneficial to the region’s economic vitality and quality of life. Building new capacity in outer suburbs of regions with little growth (i.e. Cleveland) may induce trips in those areas, but these will likely mean a corresponding decline in other facilities– which clearly does not add to quality of life or growth in the aggregate.

    • Alex

      I see a difference between opening a bottleneck (Wilson Bridge) and simply adding highway capacity. Whether you add lanes in an already developed area or in a greenfield area, you’re going to induce demand. In highly developed areas, it makes more sense to add capacity in the form of more efficient transportation, usually rail. It takes up far less space overall than a 6 or 8 or 14 lane highway and can move many more people for the space it uses. It’s also much more scalable as demand increases. Meanwhile, I does not add pollution or require as much eminent domain. Both are wins for quality of life.

      • Tim

        When it comes to social-good and sustainability I would prefer to see the consideration of prioritisation of modes as follows:

        Active transport – Walking/Cycling
        Mass-transit/Public-transport(rail/light-rail/bus)
        Private-motorised – cars, vans, etc

        Of course it depends on the types of journeys being made on the route; no-one would expect people to walk 100 miles between cities. But in urban areas where it can be shown that a reasonable share of journeys are relatively short, dedicated active-transport infrastructure should be top priority for the following reasons:
        – It can match/beat public transport for space saving
        – more sustainable, less pollution, carbon burned etc
        – much cheaper to build, maintain and use
        – more convenient in certain circumstances (ie for shorter journeys) as door-to-door, independent travel, no waiting
        – other public health benefits – exercise

        (Sorry I missed out motorbikes and in some ways I would rather see them than cars, but I don’t think motorbikes are likely to get their own dedicated infra any time soon. This is in contrast to cycling where we’ve seen dedicated subjectively safe infra is paramount if cycling is to be popular or even acceptable, much as pedestrians have sidewalks.)

  2. One of the key factors in “inducing demand” in areas of new roads, is new development. The issue should be controlling or limiting development in areas served by new roads, rather than attacking the new roads themselves. If you put in a new road to eliminate congestion, and then allow haphazard development along the length of it, well, duh, its going to increase traffic.

    Regarding adding lanes or other flow improvements to existing roads and freeways, among other benefits, it allows people who may have been clogging up surface streets to avoid congestion to take the freeway or arterial highway, creating a better quality of life in neighborhoods. Considering most long trips are for work, these people obviously were getting to and from work somehow before (again assuming no additional development because of the road improvements) and now can take the more direct route even if its not completely free of congestion. Allowing more people to travel with the same amount of congestion is still a new positive unless someone has a concern unrelated to actual traffic issues (ie environmental agendas, which are fine, but be honest about it). And, again, new development has to be taken into account in the equation, manage that better and reduce “induced demand.”

    Finally, the equation has to take into account population growth and subtract that from the increased elascity. Perhaps it already does to some extent, but I doubt it. Population growth nationally keeps skyrocketing and, for apparent political reasons, is no longer considered a policy concern or problem. This must have an impact on road use and congestion.

    It also seems quite interesting that this is another case where alleged “science” (academic fad) seems to contradict common sense. The fact that these “findings” about “induced demand” helps to validate and further the ideology of the “new urbanists” is curious to say the least. Considering the adoption of “new urbanist” ideology among many planners and academics, it smells a bit like the old “studies” that tobacco companies would put out “proving” that smoking was not harmful to one’s health,

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