This word is a little tricky — at first, the combination of mix and number in a series doesn't seem to add up to police box, but there's a catch. This word is actually an abbreviated combo of two other words: The 交 comes from 交替 (in rotation) and the 番 comes from 立番 (standing watch).

A police box is basically a tiny community police station staffed by one or two officers. It's something that is not common in many Western countries, but it is pretty much all over Japan.