"I've wanted to write for a while about [so-called] 'induced demand,' the specious argument that expanded roads just fill up with new traffic so why should we bother [building more]?
"Two articles below debunk the induced demand argument in their own ways, but here's my own TL;DR summary: Which type of infrastructure should government invest in: transit almost nobody will use, or lanes everybody will use? Induced demand is a false argument. Nobody says 'don't build a new airport terminal or runway - it will just fill up with new flights' or 'don’t build a new port terminal – it will just fill up with ships'."~ Tory Gattis from his post 'Induced Demand Debunked' [emphasis in the original]
Friday 30 June 2023
'Induced Demand': Nobody says 'don't build a new bus lane - it will just fill up with new buses'
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The induced demand claim is observably false in the Wellington area (Aucklanders may have their own observations). Both the Kapiti Expressway, now extended to Otaki, and Transmission Gully have taken a huge amount of traffic off local roads, making them much more usable for locals. And neither road has shown the slightest tendency to fill up, except at certain times at each end where they merge into inadequate continuing roads.
I can vouch that Transmission Gully, at least, has accommodated additional demand, since far more people than formerly now make regular trips from Wellington to the Kapiti beaches. That demand was, presumably, always there, but people did not bother to travel because the time taken was so long and unpredictable. The new road has not "induced" the demand, but has "accommodated" it, adding to the sum of human happiness.
The Wellington roads that are still congested are those that have been underbuilt (where 4 lanes merge into 3, or 2 into 1), or that are blocked by a series of unsynchronised traffic lights. The basis for the "induced demand" claim presumably comes from situations overseas where a 6-lane highway was needed to meet existing demand but only a 4-lane highway was built. Not surprisingly, the inadequate new road would immediately fill up.
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