From one online article, first published on the Human Events website (a conservative online magazine, I think?):

"The Texas segment of the NAFTA Super Corridor is moving rapidly toward approval. When built, the Trans-Texas Corridor, or TTC, will be a major super-highway with six lanes moving in each direction, twelve lanes across in total, described in the 4,000 page draft environmental study as including separate lanes 'for passenger vehicles and large trucks, freight railways, high-speed commuter railways, and a corridor for utilities including water lines, oil and natural gas pipelines, and transmission lines for electricity, broadband and other telecommunications services.'

The Texas Department of Transportation (TxDOT) is overseeing the Trans-Texas Corridor (TTC) as the first leg of the NAFTA Super Highway. A 4,000-page environmental impact statement has already been completed and public hearings are scheduled for five weeks, beginning next month, in July 2006. The billions involved will be provided by a foreign company, Cintra Concessions de Infraestructuras de Transporte, S.A. of Spain. As a consequence, the TTC will be privately operated, leased to the Cintra consortium to be operated as a toll-road.

The details of the NAFTA Super Highway are hidden in plain view. Still, Bush has not given speeches to bring the NAFTA Super Highway plans to the full attention of the American public. Missing in the move toward creating a North American Union is the robust public debate that preceded the decision to form the European Union. All this may be for calculated political reasons on the part of the Bush Administration. A good reason Bush does not want to secure the border with Mexico may be that the administration is trying to create express lanes for Mexican trucks to bring containers with cheap Far East goods into the heart of the U.S., all without the involvement of any U.S. union workers on the docks or in the trucks."

I've been trying to find some reasonably objective information about this to link to, but (perhaps predictably) most of what I've found thus far has been pretty biased one way or the other (pro or con)--I'll post a few links here for informational purposes, but again, it's been hard to find any "real" news coverage of this, only stuff posted & re-posted on blogs.

North America's SuperCorridor Coalition, Inc. (NASCO)

Old article (1998?), "I-35: An Interstate Become a Global Corridor"

One on DailyKos, explaining why some conservative groups are upset about this