Regional rail systems are distinguished from light rail systems in that the cars are constructed to heavy rail standards to allow them to share track and/or right-of-way with freight trains. Commonly they are based on diesel multiple units (DMUs), which are self-propelled, bidirectional, articulated passenger rail cars with diesel engines, electric generatorss and electric motors located below the passenger compartment.
Their ability to coexist with freight in the same right-of-way can drastically reduce system construction costs. Frequently they are built with dedicated tracks within that right-of-way to prevent delays.