Edited from Wikipedia
Before dining cars in passenger trains were common in the United States, a rail passenger’s option for meal service in transit was to patronize one of the roadhouses often located near the railroad’s water stops. Fare typically consisted of rancid meat, cold beans and old coffee, and such poor conditions discouraged many from making the journey.
Most railroads began offering meal service on trains even before the First Transcontinental Railroad. By the mid-1880s, dedicated dining cars were a normal part of long-distance trains from Chicago for points westward, save those of the Santa Fe, which relied on America’s first interstate network of restaurants to feed passengers en route.
The legendary “Harvey Houses,” located strategically along the line, served top-quality meals to railroad patrons during water stops and other planned layovers and were favored over in-transit facilities for all trains operating west of Kansas City.
As competition among the railroads intensified, dining car service was taken to new levels. When the Santa Fe rolled out its new “Pleasure Dome”-Lounge cars in 1951, the railroad introduced the traveling public to the Turquoise Room, promoted as “The only private dining room in the world on rails.” The room accommodated 12 guests, and could be reserved anytime for private dinner or cocktail parties, or other special functions. The room was often used by the era’s celebrities and dignitaries while traveling on the Super Chief.
In one of the most common dining car configurations, one end of the car contains a galley (with a side aisle next to it, so passengers can pass through the car to the rest of the train) while the other end supports table or booth seating on either side of a center aisle.
Trains with high demand for dining car services have sometimes featured “double-unit dining cars” consisting of two adjacent cars functioning to some extent as a single entity, generally with one car containing a galley plus table or booth seating and the other car containing table or booth seating only.
In the dining cars of Amtrak’s modern bilevel Superliner trains, booth seating on either side of a center aisle occupies almost the entire upper level, while the galley is below; food is sent to the upper level on a dumbwaiter.