The driver of a tractor-trailer was severely injured Thursday when his vehicle slammed into the rear of a second trailer that was carrying three military Humvees to a refurbishing facility in Limestone, according to Maine State Police.

The accident occurred on the Maine Turnpike near New Gloucester.

Samuel Shassner, 44, of Shippensburg, Pa., was driving the first rig and was taken to Central Maine Medical Center in Lewiston with head injuries.

The driver of the tractor-trailer that was carrying the Humvees was not injured. One of the military vehicles was knocked partially off the trailer by the impact, but wasn’t badly damaged.

The Humvees were being taken to the Maine Military Authority’s maintenance center, which has been awarded contracts from the U.S. Army since 2004 to repair Humvees that are damaged while serving overseas.

Police said Shassner will likely be charged with operating beyond his allowed hour limits if his condition improves.