In boom times, motor carriers may tolerate a few empty backhauls. But in lean years, they don't have that luxury. When operating margins are thin, just a handful of "dead-head" hauls can cause truckers' profits to evaporate.

That was the carriers' plight last year, says Rosalyn Wilson, author of the Council of Supply Chain Management Professionals' annual State of Logistics Report. "In 2006, [truckers] needed to be almost 100 percent engaged just to make ends meet," says Wilson. "Some have even reported turning down a haul if they could not get a guaranteed back haul."

The situation has created a new sort of career opportunity in logistics. Wilson reports that she's seeing the emergence of a new type of specialist, the "transportation sales agent." These sales agents, she explains, help truckers find loads to fill those empty miles, essentially serving as travel agents for freight.