A cop driving up highway looking for speeding dri vers notices a car plodding along at 18MPH. He thinks, "that's ridiculous - they're way below the speed limit" and pulls the dr iv er over.
The passengers in the car are all old women, all looking shocked and wide-eyed. The d riv er, also an old woman, was confused: "Why did you pull me over, I wasn't speeding, I was going at the correct speed limit!"
The officer replies, "No, you weren't speeding - you were going far too slow". "Slow?! I was going at the speed limit - 18MPH!"
The police officer, very surprised at this, thinks for a moment, then explains that the "18" she's referring to is in fact the route number. She realises her error, and thanks him for pointing it out.
"Just before I go" he says, "can I ask if your passengers are okay? They look rather shocked"
"Oh, don't worry about them - we just got off Route 143!"
Source: lumpyporridge.com