The past four years have been golden for transportation engineers and contractors, thanks to the 1998 Transportation Equity Act for the 21st Century, the largest public works funding measure in U.S. history. When it expires on Sept. 30, TEA-21 will have poured out more than $220 billion for highway and mass transit projects around the country, a 40% hike over the six-year program that preceded it.

As Congress now gets set to start drafting a TEA-21 successor, industry executives and state officials are pushing for an encore. They want to boost federal aid by up to 50% from the 1998 law's total. But they would be wise not to bank on such a large jump this time, because U.S. economics have changed dramatically since then.