While the number of attacks on U.S. troops in Iraq is small (relative to the number of troops and vehicles there), no one wants to get killed or maimed by a roadside bomb, RPG rocket or rifle bullets. So, in a tradition that began in World War II, troops are modifying their trucks and armored vehicles to provide more protection. The most effective measure is sandbags, as these stop fragments from roadside bombs and reduce the effectiveness of RPG rockets and rifle bullets. Putting sandbags underneath the passenger compartments of vehicles helps protect troops as well. Older flack jackets have proven useful when put over (or inside) the doors of hummers. Units that have access to welding equipment scrounge up metal (there are a lot of junked Iraqi army vehicles lying about), and weld it to trucks. This sort of effort also produces pedestal and ring gun mounts for trucks and hummers.
This points out that, even when getting ambushed, the best defense is often a good offensive. Troops are more alert and have their weapons ready when moving through hostile areas (about a third of Iraq fits that category.) This included training troops how to search in front of their vehicle for signs of an ambush. More binoculars were issued and larger convoys were led by MPs trained at this sort of thing. When possible, helicopters or UAVs flew overhead to spot attackers, and counterattack. One reason for the increased use of roadside bombs has been the growing ability of U.S. troops to spot ambushers and attack first, or respond so quickly and violently to an ambush that most Iraqis lost their heart for it.
One of the minor, but important changes is making sure all your vehicles are painted with the desert colors. Doesn't have to be camouflage pattern, just the tan CARC (Chemical Agent Resistant Coating.) This provides a measure of invisibility in the vast desert areas of Iraqi. CARC is a special paint that resists damage when trucks are decontaminated after they are hit with chemical weapons. Normal automotive paint is damaged when the decontamination fluids are used on it.
Some units have put a hummer in the lead of a convoy with just the driver and sand in the cargo bed and lots of protection added. The sand helps protect the driver if a mine is encountered, although this is only a problem when operating on dirt roads, where mines can be planted without leaving telltale signs. If ambushed, the driver of this lead vehicle has a better chance of surviving, and vehicles behind him can concentrate their fire on the ambushers.
These added defensive measures come at a cost. Additional weight (armor, sandbags, weapons) on the vehicles increases fuel use. The vigilance required while on the road tires the troops out more quickly. But as long there was a recent, or nearby, attack, it's not too difficult to keep everyone alert.