What happened to the State Troopers?

The officers go looking for help from the State Police who were assigned to the road block detail, but arrive to find the trooper car empty. There is no explanation on what happened to them. Granted the local cops operate on there own, but wouldn't the State Police dispatch realize they had some missing troopers and send others to investigate? I can under stand that the traveler took out the local cops who murdered him, but how did he get to the troopers? How did he know they would be there? They seemed to be tossed in for no reason other then to have the officers go out into the woods looking for help.