quarters. A number of these private cars have survived the decades and some are used for tour rides, leasing for private events, etc. A small number of private cars (along with other types of passenger cars), have been upgraded to meet current Amtrak regulations, and may be chartered by their owners for private travel attached to Amtrak trains. The only current example in Britain is the British Royal Train. Troop sleeper A "troop sleeper" was a railroad passenger car which had been constructed to serve as something of a mobile barracks (essentially, a sleeping car) for transporting troops over distances sufficient to require overnight accommodations. This method allowed part of the trip to be made overnight, reducing the amount of transit time required and increasing travel efficiency. Troop kitchens, rolling galleys, also joined the consists in order to provide meal service en route (the troops took their meals in their seats or bunks). Troop hospital cars, also based on the troop sleeper carbody, transported wounded servicemen and typically travelled in solid strings on special trains averaging fifteen cars each. Car technology Passenger cars are as almost as old as railroading itself, and their development paralleled that of freight cars. Early two axle cars gave way to conventional two truck construction with the floor of the car riding above the wheels; link and pin couplers gave way to automatic types. Several construction details characterized passenger equipment. Passenger trains were expected to run at higher speeds than freight service, and therefore passenger trucks evolved to allow superior ride and better tracking at those speeds. Over time, in most cases provision was made for passengers and train staff to move from car to car; therefore platforms and later vestibules were used to bridge the gap. In later years a number of changes to this basic form were introduced to allow for improvements in speed, comfort, and expense. Articulated Articulated passenger cars are becoming increasingly common in Europe and the US. This means that the passenger cars share trucks and that the passageways between them are more or less permanently attached. The cars are kept in "trainsets" and not split up during normal operations. Articulated cars have a number of advantages. They save on the total number of wheels and trucks, reducing costs and maintenance expenses. Further, movement between cars is safer and easier than with traditional designs. Finally, it is possible to implement