The TRB report, The Workforce Challenge, released June 30, says that as many as half of transportation agencies' senior staffers will retire over the next 10 years, more than twice the rate for all U.S. workers. That problem is made heightened at agencies that have had to cut staff or reduce hiring because of budget directives. Compounding the situation, the agencies now oversee a wide range of transportation modes, not just their original mandate of building roads.

"Although any one of these issues would be of concern individually, in combination they suggest an impending crisis, which--with foresight and intervention--may be averted," says the report.