A truck driver heading north on Highway 87 lost control of his semi and drove through a chain link fence into the Metra Park grounds this morning.

Montana Highway Patrol Trooper Darvin Mees said the 54-year-old driver from Bozeman told authorities a medical problem led him to lose control of the truck. The driver, who complained of back pain, was taken to an area hospital.

After plowing through the fence, the tractor trailer hit a tree and kept going for about 600 feet before coming to a stop near the park's stables. Witnesses told authorities the truck was airborne several times.

The Montana Highway Patrol is still investigating the accident, which took place at about 9:45 a.m. Mees said that at the least the driver will be required to retest for his commercial license.

The truck was marked with insignia for Hi-Ball Trucking, Inc., of Billings.