Driving around Iraq has gotten safer

U.S. Army Corps of Engineers/Washington Post

Driving around Iraq has gotten safer if you're part of a U.S. Army convoy. In January of last year, a convoy had a 1 in 5 chance of coming under attack (that's the tall bar on the left of the chart). By last December, 1 in 33 convoys were attacked (the bar on the far right). This April, it was just 1 in 100, according to data given to the Washington Post from the U.S. Army Corps of Engineers.

Why has it gotten safer? The Post's military correspondent, Tom Ricks, provides three reasons here.