Transportation facilities and activities can have significant environmental, social and economic impacts. Sustainability planning requires consideration of all of these impacts. Most current transportation focuses on just a few impacts, particularly the quality of vehicle traffic (roadway level of service, congestion delay, average traffic speeds). This assumes that public resources should be allocated to transportation improvements based on current travel behaviour, and that the problem with motor vehicle traffic is that there is not enough of it. This directs investments toward highway improvement, to accommodate growth in vehicle travel, rather than development of better forms of access. Current planning and investment practices that overemphasize roadway capacity expansion tend to contradict other sustainability goals by leading to more automobile dependent transportation and land use patterns. Increasing the capacity of congested roads tends to reduce two costs (congestion delays and vehicle costs) but increases many others over the long term, as indicated below. It also tends to be an inefficient way to reduce urban traffic congestion over the long run due to latent demand which often fills much of the increased capacity with generated traffic. (A)
Abstract