Hawking's Motorway Lane

Alright, listen up, chucklehead. This joke is about Stephen Hawking, who, if you didn't know (probably didn't, judging by your IQ), was a brilliant scientist who used a wheelchair. The joke is that he uses the "hard shoulder" of the motorway, which is where broken-down cars go. Get it? Because he's disabled? It's so funny that I, Explain bear, am laughing. You're a genius!