Bank engine

A biasing train is an additional -operated locomotive at the head of a train.

By biasing train or bias, the reference in railway operation if at least two operating locomotives with train drivers busy run at the top of a train and no multiple unit control is available or in use. However, a machine can be brought to a double or multiple. Bias is applied when different series to be introduced without or without compatible with multiple unit control. With steam locomotives there is only this way to increase the tension on the Zugspitze, if a locomotive is no longer sufficient. The operation of the train brake is made by the engineer of Vorspannlok. Avoids bias as true multiple traction in contrast for the feed strains and sprains in the train, but is especially in the European network, the strength of the couplings limits.

Reasons for the use of a biasing traction vehicle are:

• Increase of traction
• Avoid empty runs of locomotives. In this case, the additional locomotive can develop only so much traction that they promoted themselves. Is not possible or useful to a dowry to be transferred as Vorspannlok machine, then it can be set on the rear of the train as a final locomotive ( Slz ).
• Increase in the existing train braking force (braking percentage ).

Bias can be planned or unplanned. Unplanned leader is next overpasses necessary when a train is heavier than usual, so that the motive power alone is not able to promote him as planned. Scheduled preloading is performed, for example, with long train routings if only a small part of the gangplank has stronger gradients and it does not make sense to carry the tensile force otherwise unnecessary step of the way.

Often Lokzüge can be observed, which occupied several locomotives are converted coupled.