Locomotive has the same functionality as Pushcart, but is better.
The model is also better than pushcart.
You can use it by accessing the GUI and adding fuel.
You can't operate it intuitively like Pushcart because it keeps moving in that direction even if you release the key, but it moves faster.
Large Minecart is a Minecart that is twice as long as normal.
There is also one with a Large Chest.
Both can be upgraded with the Aerodynamic Minecart Upgrade Kit.
Locomotive is usually a model like Steam Locomotive, but when upgraded it becomes a futuristic model.