The latent demand in road traffic (English summary)
Use of the main road network increased by 16% from 2000 to 2012. Of this increase, it is estimated that approximately one-eighth (2%) was a consequence of the extra car use that was evoked by the completed road expansions during that same period.
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This report is available in Dutch.
At locations where road capacity was expanded due to previous congestion problems, there were during peak hours often sharp increases in traffic volumes. This primarily concerns existing traffic that, due to congestion, had previously opted to travel via other routes or avoided peak hour travel. Moreover, the road expansion also evoked totally new car use, because, for example, car passenger became car driver or because car drivers travel to destinations situated further away. This effect is however relatively limited.
These were the findings of the KiM Netherlands Institute for Transport Policy Analysis’ research publication, titled ‘The latent demand in road traffic’, which was conducted on behalf of the Ministry of Infrastructure and the Environment’s Directorate General for Accessibility. “Road expansion makes no sense, because it creates much more extra traffic, and consequently in no time the roads are full again.” A much-heard comment, but the reality reveals a more nuanced picture.
KiM defines ‘latent demand’ as the increase in car use per day on the entire motorway network (in number of vehicle kilometers travelled), which exists as a consequence of the expansion of that network. The extent of the extra car use that is manifest in capacity expansions differs strongly per expansion. On average, five years after the road network’s capacity is expanded by 10%, one can expect an effect of 3 to 5% extra car use on the network.
This report is available in Dutch.