A phenomenon affecting the gentleman when on long car journeys. When the natural harmonics of the road vibrations through the car at cruising speed, cause a usually unwelcomed lob on (aka semi, chub on, semi erect penis) for no apparent reason. Indeed you could be thinking of things entirely un-erotic.
Usually affecting the gentlemen passenger, but will hit a driver after a while. There is speculation of 'Journey Juice' affecting women, but this is unconfirmed.
Passenger: Dude, i've just got to take my seatbelt off and sort my self out.
Driver: Why, what the fuck is going on
Passenger: well i've suddenly got a tremendous Travel Lob on. Not sure why, I was just thinking about my forthcoming exam.
Driver: Oh. Oh OK.