Centre Square Fire Company was dispatched, along with Towamencin Fire Company, at 0400 hours for a vehicle accident northbound on the Northeast Extension of the Pennsylvania Turnpike, in the area of the Lansdale Interchange.  Reports were that a tractor trailer had left the road and was now in the woods.  Centre Square units arrived on location at milemarker 28 northbound to find a tractor trailer that had traveled about 100 feet off the road and into the woods  CSFC personnel provided inital medical care to the driver, who had self-extricated.  CSFC personnel also surveyed the scene to make sure there were no leaks and no risk of fire, and stood by while EMS personnel treated the driver and determined whether they would transport by ground or by air.  We also stood by until a heavy wrecker arrived and made sure the operator was comfortable retrieving the vehicle from its position without further fire department support.