In fact, all other people in the car are killed except the actor.
He is in despair and when all the fuel of the car had been used up, he shot the other people in the car with all the bullets left and only the actor is left. When he prepared to be killed by the monster, the army came and he was saved.
He regreted what he had done. It he waited a little bit longer, all the people in the car would not die. The ending is really sad.