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Scott Elaurant from Six Cats Consulting (who is both an engineer and an economist) presented his thoughts on this important topic. Induced demand has been theorised by transport economists and planners for over fifty years. It challenges the validity of both traffic modelling forecasts, and transport planning practice.
Induced Demand is the idea that building more transport infrastructure (especially roads) results in more transport demand, and is self-defeating as a means to “bust” traffic congestion. This argument has been made since soon after the first large urban freeways were constructed in the USA in the 1940s. This was the subject of a long debate, with opponents countering that unrelated population growth was the cause of the traffic growth.
This presentation looked at empirical research on induced demand over the past two decades. In the author's view, this evidence is sufficient to reach conclusions that induced demand has been proven to be valid in all jurisdictions analysed. The implications for transport modelling and planning practice are then discussed. The question of how to respond to induced demand is by no means clear cut, and a lively discussion is expected and welcome.