I saw a bus driver do that once. I was sitting at the front and just enjoyed the sight. I'm guessing he enjoyed being watched because when he noticed me, he got harder. Shame I had to get off too soon :P
Makes me think of Roadhouse Blues by The Doors:
Keep your eyes on the road, your hand upon the wheel
Yeah, we're goin' to the Roadhouse, gonna have a real, a good time