Back in December at a cargo-security forum, Rodriguez said only 20 to 30% of truck trailers are locked, a lapse he feels could enable terrorists to commandeer them or place explosives inside.

To those outside the industry, a lock on every truck seems like a simple request, but fleet operations managers see it as very complicated.

For example, how would a fleet control padlocks and keys when it has high driver turnover? How do you keep locks from freezing in cold weather? If not padlocks, then what kind of lock will be required and how much will a retrofit cost?

Jeff Davis, vp-safety at Dayton, OH-based Jet Express, says, "We have 600 trailers. If you were to add up the cost of locks, installation and labor costs, administrative costs, key distribution and backup systems, we're looking at around $150 per trailer. That's a lot of money."

Dan Fout, safety director for Garner Transportation in Findley, OH, says that since 9/11 all of their 300 trailers have been sealed. And all drivers are required to do a walk-around to check seals after a stop. "The drivers are also required to lock the tractor when they're not inside -- always."