Yesterday was a good example of why it is important to always clean your car’s windshield completely before driving. I didn’t see the accident take place, but a car that was parked on the street was pushed about fifty feet down the road, onto the grass, and into a tree. This caused quite a bit of damage to both ends of the car. The driver that hit the parked car left the scene. A few minutes later another neighbor showed up with a smashed bumper. What I think happened was this:

(Using standard cryptography alphabetical stand-in names)

It was warm but snowing (‘slushing’) just enough that car windows needed to be cleaned before driving. Alice was in a hurry and didn’t clean her windshield. In the half block between Alice’s house and where Bob was parked, Alice accelerated too much. I can tell Alice was driving too fast for a neighborhood street by how far Bob’s car was pushed given the relative masses of the two cars. Alice must have not cleaned her windshield, preventing her from seeing Bob’s car, even though it is common for a car to be parked where Bob’s was. Alice then drove back up the block, cleaned the snow off the car, and came back.

Now, imagine that instead of a parked car, it was one of the many cyclists or joggers in the neighborhood. So, please, completely clean and defrost your car’s windows before driving.