Double deck carriages date to at least as early as the second half of the 19th century. In France several hundred voitures à impériale with seats on the roof were in use by the Chemins de fer de l’Ouest, Chemins de fer de l’Est and Chemins de fer du Nord by 1870, having been in use for over 2 decades; the design was open at the sides with a light roof or awning covering the seats. In the 1860s M.J.B. Vidard introduced two-storied carriages on the Chemins de fer de l’Est, with a full body, windows, and doors; the same design lowered the floor of the lower storey to keep the center of gravity low. Vidard’s carriages had a total height of 13 feet 8 inches (4.17 m) with the head height in the lower part of the carriage only 5 feet 5 inches (1.65 m); the carriages had a capacity of 80 persons (third class) in a 2 axle vehicle of 13 tons[which?] fully loaded.
The Chicago, Burlington and Quincy Railroad placed bilevel cars in commuter service in the Chicago area in 1950. These were successful, and led to the Atchison, Topeka and Santa Fe Railway introducing long-distance Hi-Level cars on Chicago–Los Angeles El Capitan streamliner in 1954.
The double-deck design usually includes lowering the bottom floor to below the top level of the wheels, closer to the rails, and then adding an upper floor above. Such a design will fit under more bridges, tunnels and power wires (structure gauge). For cost and safety, this design also minimizes car height (loading gauge) and lowers the centre of gravity.
Depending on train station platform heights, three designs can be used for entry – high platforms require use of a “split level” car design, where the doors are located on a middle level, with access into the upper or lower level branching off – with stairs or ramps going both up and down (sometimes this configuration includes a section of seating at the middle level in the entry section, with double levels only in part of the lengths of the car). For low train station platforms, a “two-floor” design with level entry onto the lower floor is used. Occasionally a third, very tall “two floors over-wheel” design is used. This is a traditional single floor car “with a second story” design which, when using a low platform, requires steps up to a traditional floor height and then internal stairs up to the upper floor.
Platform height and floor height issuesEdit
There are four important height measurements above the railhead: platform height, traditional floor height, downstairs floor height and upstairs floor height. Platform height determines the level entry height for wheeled objects, such as luggage, strollers, wheelchairs and bicycles. Platform height is ideally standardized across all stations the train serves. Traditional rail car floor height matters for end doors connecting to existing single floor rail cars. Downstairs or lowest floor height is primarily determined by the thickness of the beams connecting the span between the wheels and bogies (trucks) of a rail car. The upstairs floor or highest floor height is above the lowest floor and must fit under bridges and tunnels. Level entry floor height must match the platform height. Hopefully either the traditional or downstairs floor height already matches the platform height. Despite the name “bilevel” or “double-decker”, for maximum compatibility the rail car will have up to four different floor heights. High platform design (Using outside steps to avoid having a level entry from the platform) is troublesome.
Common low-platform designEdit
Most low-platform double-decker trains have level entry onto the lower level of the car, allowing wheelchair access. There are two-floor heights (upstairs and downstairs) in these “bilevel” cars. There is a staircase between floors inside the car. Connecting doors between cars are either at the (higher) upper floor or at an intermediate level over the bogies. In the former case, connecting directly to a single level car causes drag and connecting door problems.
In the western USA, cars are of the upper-level-connection type. They use low-platform stations, because the traditional single floor trains all had exterior entry steps to maximize flexibility (emergency and temporary stops) and minimize infrastructure costs. There are no examples of two-floor platforms, so there are no platform doors on the upper floor. Car roof lines lengthwise are flat for connecting doors to the upstairs of bi-level cars. A Bombardier Amtrak Superliner car is 16 feet 2 inches (4,928 mm) tall.
Uncommon very tall designEdit
There are several very tall bilevel cars (e.g. Colorado Railcar has 19 feet 9 1⁄2 inches (6.033 m; 6,033 mm) . They typically are described as a traditional rail car with a second story. Most of these cars serve low platforms so they have exterior steps up to the traditional “over-wheel” floor height e.g. US 51 in (1,295 mm). End doors connect at the traditional height of existing rolling stock. Some cars have upstairs end doors as well. Many of these cars also include outside balconies on either the upper or lower level. Upstairs and downstairs connect by interior stairs. These cars can fit most able people, but lack level entry. On almost all these cars the upper level consists of a full-length glass dome. Some cars are self-propelled Multiple Units so using traditional floor heights appears fixed. In towed cars it is possible to lower the downstairs floor between the wheels/bogies so that level entry is possible with more than 500 mm (19 5⁄8 in) of added headroom and interior steps from that floor to the traditional floor.