HADITHAH, Iraq — Marines are aggressively targeting insurgents who plant roadside bombs and land mines along what’s called the “Hit-Hadithah Corridor,” a strategic stretch of desert roads running along the Euphrates River northwest of Fallujah.

The roads are used by both sides in the conflict: the U.S. military runs patrols and supply convoys; the insurgents use them to transport money, fighters and munitions in Al Anbar province.

Assembled in mobile assault platoons, or MAPs, Marines from the 1st Battalion, 23rd Marine Regiment spend long, cold patrols keeping the routes clear. From Humvees on the roads or observation posts on high ground overlooking the corridor, the Marines watch for people planting roadside bombs or other explosive devices.

And increasingly, they look for suicide car bombers.

“That’s the only thing left of that guy,” said Sgt. William Henderson, platoon sergeant of MAP 3, pointing to charred bits of twisted metal off the side of the road Thursday. The day before, a sedan painted with the orange-and-white markings of Iraqi taxicabs detonated as a U.S. convoy passed.

In that attack, only the suicide bomber was killed.

On a typical patrol, the MAP teams spend 12 hours combing the roads, checking for indications of freshly laid munitions and searching suspect vehicles. The insurgents, Marines say, tend to strike in the same spots, so careful attention is paid to several intersections and stretches of road.

On Thursday, a howling, bitterly cold wind made for a long patrol for MAP 3. Henderson and Cpl. Ben McGuire, a 25-year-old from Red Oak, Texas, took turns halting traffic while other Marines inspected the routes. Several times, warning shots were fired at vehicles acting erratically or getting too close to the Marines.

“I don’t worry about the mortars or the IEDs. I worry about the VBIEDs,” the military’s acronym for vehicle-borne improvised explosive devices, said Lance Cpl. John Knepper, a 20-year-old from Austin, Texas.

Knepper has seen firsthand what the car bombs can do. A few weeks back, a suicide bomber detonated less than 30 yards from a group of Marines; several were injured by shrapnel, but most were saved from serious injury by a thick stone wall.

“That was the biggest explosion I’ve ever seen. It was incredible,” said Knepper, who still has pieces of shrapnel in his arm from a land mine encountered on a different patrol.

Late in the afternoon, the Marines of MAP 3 pulled off the roads and patrolled near an old Iraqi military outpost. Nearby, then found a terrain model made of small stones on the desert floor; an arrow pointed north, and other lines of stones formed buildings and roads. The Marines guessed it was made by insurgents.

The patrol then occupied a strategic overlook, using high-powered optics to watch the traffic below. Traffic in the area has picked up in recent days, the Marines said, as many locals start the Hajj, the annual Muslim pilgrimage to Mecca.

The Marines watched for people dropping or burying explosive devices on the roads, and also for vehicles bearing the hallmarks of car bombs: erratic driving, single occupants, cars riding low to the ground.

They radioed suspicious vehicles to a nearby sniper team, also tracking the roads and ready to stop anyone wanting to make this piece of the corridor a little more dangerous.