The U.S. Department of Transportation is requesting proposals for ways to relieve traffic congestion at the Canadian and Mexican borders, saying that this congestion is “stifling commerce.”

Transportation Secretary Mary Peters noted that the value of freight shipments between the three US, Canada and Mexico increases 8 percent per year, and has gone up 170 percent in the past 20. Traffic delays at the Canadian border alone cost businesses $!4 billion per year, she said.