they just had a trivia question on the radio, what part of a car travels the most

the keys.

Even when you park the car, you take the keys with you where ever you go.

Everything that instantly throught, "well the keys aren't part of a car" can shut up and move along. They sell you the keys and car as a single transaction. The keys do nothing without the car, and the car does nothing without the keys. Just like the car battery, that we are really lucky to not have to carry around like the keys.