The Quadrail is a train system including multiple tracks, each consisting of four rails, wrapped inside of a tube. The tube is intended to operate at vacuum, although leakage through the pressure seals at the stations over hundreds of years has allowed a small air pressure to accumulate. The tube allows for faster-than-light transport through most of the known galaxy and includes the 12 Empires recognized in Zahn's Quadrail series.
At the core of the Quadrail is a "quantum thread" known as the Coreline. The Coreline is the mechanism which accelerates the Quadrail train system through an unexplained physical phenomenon, although the passengers aren't aware of this (general speculation is that one of the four rails provides the motive power). Standard Quadrail trains can travel at up to a light-year a minute, but in all actuality, train speed is controlled by proximity to the Coreline (e.g. the closer an object gets to the Coreline, the faster it moves). Therefore, some specialized Quadrail maintenance trains can travel faster than standard Quadrail trains.
The Quadrail is operated throughout the Galaxy by the Spiders - an enigmatic race with long mechanical spider like legs and spherical bodies.
There are three classes of seating on a typical Quadrail train - First, Second, and Third. Among the different types of cars are compartment cars, only available in first class, coach (seating) cars, available in all three classes with decreasing comfort depending on the class, dining cars, available in all three classes with decreasing conveniences and selections depending on the class, recreation/entertainment cars, which include exercise facilities and bathing facilities, available in all three classes, and baggage cars. Typically a train will have, going from front to back, an engine car, which is not internally accessible, one or more compartment cars (individual compartments have sleeping, bathing and toilet facilities), one or more first class seating cars, a first class dining car, a first class recreation/entertainment car, second class seating, dining and entertainment cars, third class seating, dining and entertainment cars, and one or more baggage cars. The cars are internally pressurized and are joined by pass-through airlocks. Passage from one car to another is controlled by the class of ticket, with each class ticket giving entry to its own class and lesser class cars. Each class has a first aid station/infirmary, located either in the dining car or the entertainment car.
Known Quadrail stations
- Terran Federation
- New Tigris
- Night Train to Rigel (2005)
- The Third Lynx (2007)
- Odd Girl Out (2008)
- The Domino Pattern (2010)
- Judgment at Proteus (2012)