Induced traffic, for those not in the know, is, according to StreetsWiki, is "the phenomenon whereby decreasing the cost of vehicle trips in a particular corridor -- usually by decreasing congestion through a roadway improvement -– induces new vehicle trips in that corridor."

A new research paper from professors at Aalborg University in Denmark and the Institute of Transport Economics in Norway says that the cost-benefit analyses for new roads in Europe still suffer from a lack of recognition for the induced traffic phenomenon:

"By exaggerating the economic benefits of road capacity increase and underestimating its negative effects, omission of induced traffic can result in over-allocation of public money on road construction and correspondingly less focus on other ways of dealing with congestion and environmental problems in urban areas," according to the report summary.

The effect is illustrated through a case study of a new road project in Copenhagen, where a more sophisticated representation of travel behaviour resulted in 40% less benefits compared to traditional approaches. The researchers argue for transport models to focus more on pedagogy than precision, to reduce the risk of policy makers misleading both themselves and the public.

The full report is available as a free PDF download.

Thanks to Morten Skou Nicolaisen