This year's study measures the predictability of congestion in a new "planning time index." It shows that Georgia freeway drivers have a better idea than some others of how long a drive will take, and don't waste as much time building in an unnecessary buffer around everything they schedule.
The report from Texas A&M Transportation Institute found that Americans are adapting to road congestion by allowing, on average, an hour to make a trip that would take 20 minutes without traffic.
The report ranked the Atlanta area's overall traffic seventh-slowest in the nation.

http://accesswdun.com/article/2013/2/257985