A few months ago, I wrote about induced demand, or the tendency of supply to create demand. In other words and in this context, that means more roads breed more drivers, which in turns results in more traffic. The idea here is that practically speaking, no matter how many roads we build, they will never eliminate traffic.
A recent report, however, suggests that this phenomenon is often overlooked, leading to new roads that don’t produce as much benefit as they should. The report was picked up by Planetizen, The Atlantic Cities and Streetsblog, among others. I found the Streetsblog post the most interesting, as it points out that,
Nearly every time a new road is built, traffic volume increases beyond the predictions of the traffic studies. And nearly every time, transportation planners are surprised.
The explanation is a wonky little phenomenon called “induced demand.” Essentially, if you widen roads to reduce congestion, people who were avoiding the road because of congestion will find it more convenient and take more trips, thus increasing traffic again.
Commenting directly on the study, the post continues,
According to the study, completed by researchers at the Institute of Transport Economics and a Danish university, this leads to skewed cost-benefit analyses that call for new highways and road widenings of dubious benefit to the public.
Researchers reported that perceived time savings make up the largest portion — sometimes 85 percent — of the economic benefits assigned to prospective highway projects. But an unanticipated boost in traffic volume can turn many projects that would theoretically pass analytical muster into economic losers. Unless transportation agencies are carefully accounting for these effects, however, many of these projects get built anyway.
I always find it astonishing that so-called experts overlook things that even amateurs can understand and see a need for. But apparently they do.