Flutterby™! : Induced Travel

Federal Highways Administration: "Is Induced Travel Real?":

Economists use the term "induced travel" to describe the additional demand for travel that occurs as a result of a decrease in the generalized cost of travel, including both travel-time and out-of-pocket costs. However, this term is often misused to imply that increases in highway capacity are directly responsible for increases in traffic. ...

FHWA: Economic Analysis Primer: Forecasting Traffic for Benefit Calculations then goes on to state that drivers who formerly avoided trips or used alternate routes will now use the new routes, and that:

Other drivers will "unchain" existing trips into multiple trips or make new trips that they might otherwise have avoided due to excessive delay associated with congestion. Some individuals may shift from transit to automobile. Drivers may also make longer trips (to more remote locations) than they did before the improvement. Other traffic responses can and do occur.

The real question here is: how come traffic engineers don't have more incidents of spontaneously exploding heads?