How do trains pull so much weight? I’ve seem them with hundreds of freight and gas tanker cars.
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Steel wheels in steel track have very little compression so the rolling resistance. If you compare it to rubber tires in a truck it is an 85-99% reduction.
Air resistance has the most effect on the front and rear of a vehicle. It is less along the sides of a vheicle. Even if there is a gap between wagons there is a reduction in air resistance compared to if it is separate. So more wagons/trailers are more efficient the fewer in regard to air resistance. The same is also true for trailers on a truck.
Trucks with multiple trailers are allowed in a simple location like the Australian outback [https://en.wikipedia.org/wiki/Road_train](https://en.wikipedia.org/wiki/Road_train) four trailers are allowed in some locations. That is more efficient if split into separate trucks. It is how the road network is built with limitations on for example bridges, road culvers, intersections size, and interaction with other vehicles that is that limitation.
The train also accelerates a lot slower than trucks, it would be problematic for other vehicles if they accelerated as slowly as trains. The max incline of a track is lower than roads which means less power is required to go up a hill. The speed is also in general lower for freight trains and air resistance, at least for the front increase with the square of the speed. All of this results in that trains can have less power per tonne of cargo, that is in addition to the reduced rolling resistance.
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