By Hugh Sykes
BBC News, Baghdad
The people of Baghdad woke up this morning to new security measures intended to stop car bomb attacks.
Checkpoints present easy targets for car bombers
But two car bombs had already exploded in the city before midday local time, killing two people and injuring 10. Five of the injured were police officers - the bombs targeted police patrols.
The security plan is called Operation Forward Together. The regular night-time curfew has been extended, there is a new hotline for anonymous tip-offs and there are extra checkpoints and police patrols all over Baghdad.
The national security adviser, Mowaffak al-Rubbaie, says it is intended to step up pressure on al-Qaeda in Baghdad.
But it is a gamble. Checkpoints and patrols present easy targets for car bombers intent on killing security forces.
And ordering a suicide car bomber to pull over could prompt the bomber to detonate, and so actually help him to achieve his objective.
The main effect of the new clampdown so far has been to create massive traffic jams.
An Iraqi colleague who usually takes 20 minutes to drive to his office in the city centre took an hour and a quarter this morning.
Generally, he has to go through two checkpoints. This morning there were six. I asked if he was thoroughly checked - "No," he said, "Just waved through."
His daughter is sitting university exams - they start at 1000. She lives 15 minutes' drive away, but to be sure of being on time, the shuttle bus came to pick her up with three hours to spare.
Reaction to Operation Forward Together has been mixed.
One man told the BBC: "We've seen it all before - it's mostly useless".
Another said: "We don't trust the checkpoints."
The Association of Muslim Scholars is deeply critical. They suspect this operation will be used as an excuse to raid Sunni Arab homes without good reason.
But others are pleased: "More checks are better - we'll feel safer," was one comment.
"Never mind the traffic jams. It's worth it if it reduces the danger," someone else said.