Considering they have a pact with the other station, the route should be familiar to them. Briggs really confirms that saying "the helicopter" when talking through the radio with his base.
They approach the car with caution because the body outside the car: a man with a gun in his hand and a bullet in the head (he killed himself). Briggs looked inside the car and saw a woman and a kid dead in the same way (probably a family). The surprise could be because they didn't expect to find these bodies there, only an empty car. This family should be "survivors" from the other station which reached that place but couldn't walk anymore (e.g. too tired, no food, no water, no shelter).
