Speed Limits - A Bit of Humor

A police officer had just pulled over a car full of nuns for going too slow on a major highway. The conversation went like this:
Police officer: "Why were you driving so slowly?"
Nun driver: "I kept seeing all these signs with the number 20 on them and figured that was the speed limit."
Police officer: "No, Sister, that is the highway number."
Nun: "Oh, I'm so sorry, Officer, I didn't know that."
Then the police officer looks into the back seat and sees that the nuns there have panic-stricken faces and white knuckles from holding on to each other too tightly.
Police officer: "What's wrong with the nuns in the back seat?"
Nun: "Oh, we just got off Highway 101 a few miles ago."