a regular passenger car. The most common combination is that of a coach and a baggage car, but the combination of coach and post office car was also common. Combines were used most frequently on branch lines and short line railroads where there wasn't necessarily enough traffic to economically justify single-purpose cars. As lightweight cars began to appear on railroads, passenger cars more frequently combined features of two or more car types on one car, and the classic heavyweight combine fell out of use. Control car (cab) A control car (also known as a Driving Trailer in Europe and the UK) is a passenger car which lets the train be run in reverse with the locomotive at the back. It is common on commuter trains in the US, Canada and Europe. This can be important for serving small towns without extensive switching facilities, end train stations, dead-end lines, and having a fast turnaround when changing directions in commuter service. Dome car A dome car can include features of a coach car, sleeping car, a lounge car, dining car, and an observation car. Within the United States, the primary manufacturers were The Budd Company (stainless steel construction), The Pullman Company (steel construction), and ACF (American Car & Foundry, aluminum construction). A portion of the car, usually in the center, is split between two levels, with stairs leading both up and down from the train's regular passenger car floor level. The lower level of the dome usually consisted of a small lounge area, while the upper portion was usually coach or lounge seating within a "bubble" of glass on the car's roof. Budd Co. dome cars used curved class, whereas Pullman company cars used flat panels of glass that were positioned at different angles above the roofline. Passengers in the upper portion of the dome were able to see in all directions from a vantage point above the train's roof line. On some dome cars, the lower portion was built as a galley, where car attendants used dumbwaiters to transfer items between the galley and a dining area in the dome portion of the car. In the United States, the Union Pacific railroad was the primary user of dome dining cars in the pre-Amtrak era. Some dome cars were built with the dome extending the entire length of the car (a "full dome" car), while others had only a small observation bubble.