A runaway, three-quarter ton truck, owned by the Somerset Valley Construction Company in New Jersey, the firm engaged in the sewer project on the west side of the community, crashed into the rear of the Court House at 2:15 p.m. today after going through a railing and over a 25 foot drop from Packer Hill, not far from the Soldiers Monument. Michael SanFelice, 49, of Norristown, N.J., operator of the vehicle, said he parked the truck and was talking William Bargart, project engineer, when the truck suddenly started to move.