Trains have a certain train configuration. This refers to how individual train sections can be combined to form an entire train set. Locomotive-hauled trains are a classic example of this, but not only in freight traffic. They also used in passenger traffic. However, they are increasingly being replaced by multiple units. These are closed vehicle units that can only be separated for workshop purposes, but no longer for operational reasons.
How the car bodies and their axles are arranged, or where the traction motor is installed, these are all criteria for the classification of trains. But there are more than the before mentioned. Each train configuration has its advantages and disadvantages. Usually, they are system decisions adapted to the environment that we deal with in this chapter.