Products in the range have included locomotives, tracks, rolling stock, stations, signal boxes, and other track-side buildings and accessories.

The design of Lego trains has developed substantially, with several different systems introduced, with varying degrees of cross-compatibility.

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.

The motors were the same size, the push trains used a motor-shaped dummy block of bricks, and all used the same wheel style.

The colour of the tracks was changed from blue to grey, and the 12-volt transformer changed to support utility functions in a more streamlined style with control switches that docked alongside the transformer, following the design style of increasingly streamlined model train controls of the time.

The utility functions now included remotely controlled points, signals, wagon de-couplers and level crossings.

The models gained a much more realistic appearance, including some with much longer carriage/wagon bodies and swivel bogies, and there were special windows which simulated having a pull-down glass section.

Stickers were included allowing the owner to bedeck their trains with symbols of several European railway companies, such as DB, ÖBB, NS, SBB, DSB, NSB, VR, and British Rail.

The railcar bases were now again assembled from train-specific wheels and coupler and a greatly increased number of universal pieces.

As with the previous generation, the electrical parts such as the train motor (7865) and the mains transformer unit (7864) were manufactured by Bühler on behalf of Lego.

Owners with a worn out red motor had no option but to replace it with a standard black one (7865) or break open the sealed unit and transplant the components.

The 12-volt line was promoted in a 1983 UK television advert featuring a group of adults planning a 'mail train robbery'.

Lego continued to supply accessories (but not complete sets) for the 12V system via its mail order service until 1993.

To enable the models to be battery-powered, the powered vehicles had a specific train base, which was 6 studs wide to accommodate a snap-fitting battery pack.

However, the infrared remote control introduced problems of range, and the use of batteries required them to be replaced or recharged at regular intervals.

The announcement cited a lack of sufficient demand for the 9-volt product line to be profitable, caused partly by the need to replace key machinery and place minimum orders for motors and power regulators.

The new range was announced as launching in 2009, and would use the new 'Power Functions' system also used in the Technic line, which would allow the company to "amortize the development and on going cost across multiple themes".

Necessary part numbers were listed on the rear of the box to convert the Emerald Night to a Power Functions compatible train.

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