Fees
Fees are costs bound to either motorized rail vehicles or orders. Fees for motorized rail vehicles are always bound to a single vehicle, such as a locomotive. Fees for the orders, on the other hand, can be bound to multiple vehicles that are assigned to an order, and include costs of both relevant cars and cargo. Each fee can be broken into individual costs per vehicle, such as the consumed diesel, body damage, environment impact, and others. This full listing is accessed by printing out a fee on a career manager.
It's your responsibility to take care of the fees. Otherwise, you will be blocked from buying new licenses and can also get suspended from taking new delivery orders.
At the start of a career, fees are negligible due to insurance covering all costs in excess of $100. However, as your career advances, you share more of the responsibility of paying for maintenance. This incentivizes you to treat all equipment and deliveries with utmost care, skill and efficacy.
Servicing a motorized vehicle by paying a fee will instantly repair and restock it to a mint state. This is a preferred way of servicing vehicles at the start of your career, when copay is low enough. Later in your career, manual servicing is a cheaper alternative.
You are not necessarily required to pay their fees as soon as they come up. Sometimes it's better to time these payments strategically.