They cobbled the roads through their section of the reserve to limit people, speed and traffic.

"That's a good idea, to limit traffic to the city," he said.

The river's irregular flow strongly limits traffic on it, in particular at its ascent, though this can be overcome by boats being given a tow.

All have airlines that have elected on their own to limit traffic to no more than the runways can handle, officials say.

"If you're limiting upstream traffic, you're not going to see upstream traffic," Wade counters.

Even as the occupying authorities tried to limit such traffic, the underground railroad became more organized.

Newark International Airport was forced to limit traffic to a single runway through much of the morning, causing some delays.

Like other ancient cities, Rome is ill-suited for automobiles and has struggled to find ways to limit traffic without upsetting its citizenry.

A Pentagon official said that while Syria had done some things to limit militant cross-border traffic, "they have not done nearly enough."

Mr. Kiley said he believed that measures to limit traffic on some highways and bridges, like tolls, were overdue.