Mel Gibson must have a British truck, because the steering wheel is on the opposite side of most American cars. But the goof is actually when the bus driver looks at Mel's truck in the mirror. The image is not reversed.
Edit: It's not British and it's not a goof, it's an Australian truck. The scene is a parody of Mad Max 2 (The Road Warrior), an Australian film which launched Mel Gibson's career with American audiences. (Mel Gibson is Australian, if you weren't aware.)