Those are not tanks, but many think they are. These are half the weight of a tank, so the train can carry two per car. What you see here are the Bradley Fighting Vehicles, which replaced the old boxy APC (Armored Personnel Carrier). The Bradley has a turret with a 25MM chain gun (fires like a slow machine gun), and this turret often makes people think it's a tank. That main gun in the turret is designed to be able to engage and neutralize medium targets like trucks, enemy APCs and the like. The interior of the vehicle is designed to carry a squad of infantry soldiers who also can shoot outside the vehicle using a highly-modified M-16 which has no handgrip in the forearm, but has a rather naked barrel (with no front sight)terminating in a big screw-like bushing. The Bradley has a number of hollow ball-shaped mounts for these rifles. You stick the rifle through the hole in the ball, and screw it into threads in the ball. Then you swivel it using the ball to fire in different directions. YOu look out of small periscopes to fire these side-mounted weapons. The Bradley has a big door in the back (similar to the old APC), that opens so the infantry troops can dismount and attack. I can see that these Bradleys are also equipped with the TOW anti-tank missiles (located in big boxes on the side of the turret) The Bradley is faster than the old APC, and was designed to be able to stay-up with the much faster tanks, the M-1A1 Abrams, on the battlefield. The Bradley is motivated by a large diesel engine which blows black smoke up into the air, making the occupants nervous on the battlefield. These Bradleys were likely on the way from Ft. Carson (at Colo Spgs) to the NTC in California for desert exercisesm or maybe to Pinon Canyon maneuver area. Although, they might have been on the way to or from Iraq, since the photo was taken in 2007.
Want to know more? see http://www.fas.org/man/dod-101/sys/land/m2.htm