Continuity mistake: Throughout the movie, there is a family picture that disappears and reappears on the driver's side sun visor.
Continuity mistake: While David is sitting at the table in Chuck's Cafe, the ashtray is unused, but moves around the table several times. Cutlery changes position too, in two different shots.
Chosen answer: The movie opens with him in downtown Los Angeles, California, so he's probably from there or somewhere in Southern California. He's heading to Bakersfield, California, which is north, about 2 hours away. In the short story, he's heading to a client in San Francisco. However, in the film he gets off the main freeway running from LA to Bakersfield (IH-5) and takes Highway 14 towards Canyon Country.
Bishop73