“by train”意为“乘火车;坐火车(作为出行方式)”。常用于说明交通工具或旅行方式。(类似表达还有 by bus / by plane 等。)
/baɪ treɪn/
I go to work by train.
我乘火车去上班。
Because the roads were blocked by snow, we decided to travel by train instead of driving.
由于道路被大雪封住,我们决定改乘火车出行,而不是开车。
“by”在这里表示“通过某种方式/手段”,后接交通工具名词(通常不加冠词),构成固定结构:by + 交通工具(by train / by subway / by taxi 等)。这种用法强调“方式”,而不是具体哪一列火车。