A koban — a small neighborhood police box/station where officers patrol, give directions, and take reports of lost property.
道に迷ったので、近くの交番で聞いた。
I got lost, so I asked at a nearby koban.
交番には地域の地図が置いてあることが多い。
Koban often have local maps available.
子どもが交番に保護されて、連絡が来た。
A child was taken to the koban for safekeeping, and we were contacted.
Alternation or taking turns (an old or literary usage); not commonly used in everyday speech.
昼と夜が交番に訪れる（文語的表現）。
Day and night come in alternation (literary expression).
In physics and related fields, used prenominally to mean 'alternating' (e.g., '交番電流' as an expression for alternating current); a technical usage.
教科書では交番電流について簡単に説明している。
The textbook briefly explains alternating current (referred to here as 交番電流).