Ian Stewart's article in Scientific American was based on "Train Sets" by Adam Chalcraft and Michael Greene (Eureka 53, pp. 5–12), which also provides the basis

Ian Stewart's article in Scientific American was based on "Train Sets" by Adam Chalcraft and Michael Greene (Eureka 53, pp. 5–12), which also provides the basis of the Duplo constructions. (But note that Duplo has linked points as well as sprung and lazy points, which allows for more compact constructions.) http://www.monochrom.at/turingtrainterminal/Chalcraft.pdf http://www.monochrom.at/turingtrainterminal/Chalcraft.pdf