In December 2018 the Transportation Research Board’s Future Interstate Study Committee released its long-awaited report, Renewing the National Commitment to the Interstate Highway System: A Foundation for the Future. At 649 pages, including 10 appendices, it makes a powerful, evidence-based case that the Interstates are wearing out and need what amounts to replacement. Unfortunately, the report’s main recommendation—a huge increase in federal fuel taxes to support reconstructing the system using the original 90 percent federal and 10 percent state funding program—is both highly unlikely and inadvisable.
The committee’s findings are very important. First, most of the Interstate System already has, or soon will have, exceeded its original design life and will need reconstruction. A large fraction will likely require full-depth pavement replacement, from the sub-base up— and yet there are no real data available on the extent of this need, and the federal Highway Economic Requirements System includes no unit costs (per lane-mile) for this most expensive kind of reconstruction. Hence, the reconstruction cost estimates in the report may well be under-estimates.
Second, contrary to widespread assertions during the last decade that the era of traffic growth had ended, we now have renewed annual growth in vehicle-miles of travel (VMT), with truck VMT growing faster than passenger-vehicle VMT. The report uses a baseline figure of 1.5 percent for overall annual VMT growth, with lower and upper bounds of 0.75 percent and 2 percent. This growth supports the need for widening many corridors—and to minimize inconvenience to highway users if a stretch of Interstate needs widening, it’s best to do this as part of the planned reconstruction process.