MAP-21 also charts other important changes in transportation policy, particularly through provisions aimed at shaving years from projects' schedules by speeding environmental reviews.

Among the changes are provisions to exclude more highway and transit projects from the National Environmental Policy Act (NEPA) review process. Even before MAP-21, the vast majority of highway projects already had such "categorical exclusions" from NEPA because they were judged not to produce significant effects on the environment. But MAP-21 goes further, directing exclusions for all projects that get less than $5 million in federal funds; new projects in an existing highway or rail right-of-way; and repairs to roads or bridges damaged in natural disasters.

It also allows states to acquire real estate for a project, issue requests for proposals, award preconstruction services contracts and issue notices to proceed with preliminary design before the NEPA review process is finished.

David Bauer, American Road & Transportation Builders Association senior vice president for government relations, says the "streamlining" section "has the potential of having a big benefit," but adds that those benefits will take time to be realized.

Environmental groups criticized the project-review and other provisions. Deron Lovaas, Natural Resources Defense Council transportation policy director, says that, in the past, agencies excluded some projects from NEPA through administrative actions. "At least administratively, you have a chance to debate whether a new exclusion makes sense," he says. But now with MAP-21 statutory exclusions, Lovaas says, "That's a much broader brush that you're painting with."

The new law also requires states to use performance measurements to evaluate their transportation programs and shrinks the number of federal surface-transportation programs and funding categories by about two-thirds.

The statute changes the transportation "enhancements" program, which funded projects such as bicycle and pedestrian paths. Enhancements had many defenders and a mandatory funding set-aside. But it drew fire from some in Congress who saw the set-aside as diverting money from road and bridge projects. MAP-21 merges enhancements with programs for trails and safe routes to schools into a new Transportation Alternatives category. It still has a set-aside, but half of the program's funding will go to localities and half to states, which formerly got all the enhancements funds.

Industry officials like many parts of MAP-21 but know it only postpones the day of reckoning for the Highway Trust Fund. The fund's motor-fuel tax revenue has been pinched by more fuel-efficient cars and the sluggish economy's impact on motorists' miles driven. Congress kept the trust fund in the black thanks to $34.5 billion in transfers from the general fund since 2008. MAP-21 gives the trust fund a further $18.8-billion general-fund infusion, but even so, CBO estimates the trust fund "would be exhausted in fiscal 2015."

ARTBA's Bauer says MAP-21 "will prevent a [trust-fund] solvency crisis for the next couple of years. But at the end of 2014, we're right back into … the dilemma that vexed people for the last three years, and that is: How do we fund infrastructure investments in the future?"

Some non-transportation provisions are tacked on to the MAP-21 legislation. The RESTORE Act should be a plus for construction: It directs 80% of Clean Water Act penalties against oil giant BP after the 2010 Gulf of Mexico oil spill to go to Gulf Coast states for environmental restoration and economic development.

Other non-transportation provisions dropped out, notably House proposals to mandate quick federal approval of the Keystone XL pipeline and block the Environmental Protection Agency from regulating coal ash as hazardous waste.