Articles and means of transport.

By means of transport:

• ❎ By a land.
• ❎ By a sea.
• ❎ By a bus.
• ❎ By a taxi.
• ❎ By a plane.

• ❎ By the land.
• ❎ By the sea.
• ❎ By the bus.
• ❎ By the taxi.

• ✅ By land
• ✅ By sea
• ✅ By bus
• ✅ By taxi
• ✅ By plane

He goes to Pune by air.

But, when the means of transport is used as a countable noun:
- A/an is used.

He has to buy a car.

🧠 The + means of transport:

• ✅ Ride on the bicycle.
• ✅ Sit on the bicycle.
• ✅ Sit in the car.
• ✅ Catch the train.

• ❎ Ride on a bicycle.
• ❎ Sit in a car.

But,
✅ Take a train.