Whether he saw it out of his peripheral vision or had mystical lizard-sense, and whether the vehicles seemed to sneak up on him despite how unrealistic that is, the rest of the fucking movie was awesome, and that opening scene shouldn't ruin the rest of it. It is fine if you don't like the movie, but that scene shouldn't be any part of any actual reason, because it is purposely just a fun/convenient scene to let him do a voice over, struggle to piss, eat a lizard, and then get a cool shot of cars racing past the camera from behind, all leading up to him getting captured. Period.