M.U.

Multiple unit, a method of controlling several diesel or electric cars or locomotives from one cab. M.U. cars are electric passenger cars for operation on electrified portions of a steam or diesel railroad, as in a suburban district. Interurbans, subway cars, and RDCs are technically M.U. cars, but the term is usually reserved for steam road electric cars.

Main line

The track serving as the main route for trains. Some heavy-use lines have two or more main tracks.

Maintenance of way equipment

The machinery and rolling stock used to keep track and roadbed in good condition.

Markers

Lamps formerly hung on the rear of the last car of the train to show that the cars are indeed a train and to indicate its status. Later substitutes were used, such as reflector paddles. Now replaced on freight trains by end-of-train (EDT) devices; passenger trains now typically have built-in marker lights.

Matte medium

An artist’s material used as an adhesive for ballast and scenery materials.

Milepost

A trackside sign with a number indicating the distance from an established starting point.

Module

A section of a layout built following a standard pattern or dimensions. Each module can be connected interchangeably with any other module built to the same standards. Ntrak is an organization that has developed standards for N scale modules.

MOW

Maintenance of way, the job of keeping track and roadbed in good condition.