FALLUJAH, Iraq – The last car bomb in Fallujah exploded in May.

On that warm evening, insurgents drove a vehicle packed with explosives into mourners for a slain local tribal leader as they wound through a ramshackle corner of the city, killing 20. The next day, Fallujah’s mayor banned all vehicles from city streets.

If there were no cars, reasoned Mayor Saad Awad Rashid, there could be no car bombs.

“It stopped,” said Lt. Col. William Mullen, commander of a shrinking force of U.S. Marines in the city who have watched the insurgency melt into the encircling countryside.

“The “significant events’ in the city stopped. I think a lot of (the insurgents) left,” he said.

The Americans are not far behind: After surrounding the city with walls and improving security on its streets, the Marines are pulling back from the one-time insurgent bastion of Fallujah. They are redeploying to surrounding areas as the U.S. troop surge allows them to consolidate progress made largely by tribal leaders and local officials in security and civil works.

They leave behind a city devastated by years of fighting and starved for reconstruction, as well as questions about whether Fallujah – a place infamous for the 2004 mob killings of four American contractors and two resulting U.S. offensives – can now serve as a model of stability for a wider American troop withdrawal from Iraq in the months and years to come.

It has been a workable but messy solution, with successes like the reduction in car bombs coming as much from the mayor’s spur-of-the-moment decisions as any military planning.

A partially trained Iraqi police force and bands of armed volunteers now work under American supervision, carefully preserving peace on streets covered by years of trash and rubble.

To live under this new protection, most of Fallujah’s 250,000 residents submitted fingerprints and retina scans to get ID cards that let them stay in the city.