All three kinds (push trains, 4.5-volt battery-operated trains and 12-volt electric trains) existed alongside each other and even allowed for upgrades.
In 1972, 4.5-volt trains gained a monolithic railcar that carried the batteries and contained both a bottom-mounted stop button to be actuated by signals, as well as a side-mounted lever for manual go/stop/back control and tripping by a track-side pivot. Set number 115 introduced 4.5 volt battery-operated trains (initially the battery box was handheld, but train sets soon contained a railcar that carried the battery box), and train sets numbered 720 (1969) and up operated on 12-volt electrified rails, introduced in 1969. The train sets used blue rails, and the first train sets were simply push-along. Lego trains were first introduced in 1966 with Lego set number 080. The design of Lego trains has developed substantially, with several different systems introduced, with varying degrees of cross-compatibility. Lego trains use a nominal gauge of 37.5 mm ( 1 + 15⁄ 32 in), based on 5-stud track centerlines gauge, corresponding with a circa 1:38 scale. The train system is sometimes referred to as 'L-gauge' among Lego fans, in reference to traditional model railway scales.
The theme is popular among adult fans, as well as children, and has spawned international associations and conventions. Products in the range have included locomotives, tracks, rolling stock, stations, signal boxes, and other track-side buildings and accessories. The Lego Trains theme became a sub-theme of Lego City in 2006. Lego Trains is a product range and theme of the construction toy Lego, which incorporates buildable train sets. One section of a massive Lego train layout at the National Train Show in Cincinnati, Ohio, July 9, 2005