前後

1. Origins, structure, and basic meaning

• Structure: 前後 (ぜんご) can denote temporal before-and-after or spatial front-and-back. 事故の前後に is temporal; 列の前後を is spatial.
• Basic usage: One example recounts events around an accident, and the other checks both ends of a line.

2. Common pitfalls and similar expressions

• Time around an event and space around a line
  • The reference nouns 事故 and 列 select temporal and spatial readings respectively. These examples do not support extending 前後 to its approximate-quantity use.