by bike = on the bike

by taxi = in the taxi

by plane / air = on / in the plane

by subway = on / in the subway

by train = in / on the train

by bus = on the bus

by bike = on the / one’s bike

“by + 表示交通工具的单数名词”在句中作方式状语，相当于“on / in + 限定词 + 表示交通工具的名词”，在对它们进行特殊提问的时候都要使用how。所以这两种情况在句中都是作方式状语。例如：

1.How does she get to school?

She gets to school by car / in the car.

2.How do you often go to school?

We often go to school on the school bus.

3.How does he often go to school?

He goes to school in his father’s car.