If you've played this game on the XBOX 360 version, you know what this is. After shortly advancing through the story, you'll reach a point where to go outside the mall and there will be a cut scene of three convicts in orange suits driving a jeep. After the cutscene, if you have any survivors with you, you should not fight the convicts yet. Once you have no survivors with you, go outside and fight the convicts. The guy on the machine gun will be a pain in the butt, but the driver has a tendency to get stuck on trees.
You can either shoot them with a ranged weapon, or melee attack them when they get stuck on a tree.
They don't have much health, as only a few hits from just a baseball bat will kill each one. You must kill all three and then drive the vehicle. You can also then use the machine gun on the back, but it's a two handed weapon so you won't be able to switch weapons without dropping it.
Here's a video if you'd prefer to watch