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I would like to purchase some used lego train tracks off ebay. I am not, however, very familiar with the different choices of track systems are out there that I might come across. So I would like to learn more about the existing types of track systems. What kinds has lego used at various eras in their history? Are they inter-changable? If I'd like train tracks that are compatible with the currently available new lego city train sets, what types of tracks should I consider?

If possible, I'd love to see photos of a basic piece of each kind side by side to see the differences.

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The LEGO train systems are all roughly compatible. They all use a 6 stud gauge, so with a bit of fiddling, you can use all of the systems together. If you want to be most compatible with the current track offerings, you're better off with 9V and RC/PF track. This question discusses the specific compatibility issues in more detail.

The different types of train track can be divided into a few main eras.

Blue Era (1966 - 1980)

A track section consisted of 2 rails connected by regular 2x8 plates. The rails themselves were blue.

blue straight rails

Trains could be either pushed by hand along the track, powered via 3 batteries (4.5V system), or powered via a third conducting rail added to the center of the track (12V system). Here are what the conducting rails for the 12V system look like:

12V conducting rails

Some people still prefer the 12V system because it included more remote controlled components than the later 9V or RC/PF systems. With later systems, the only thing that is easily remote controlled is the train itself, whereas the 12V system included remote controlled points, light, and decouplers.

Each era included straight track, curved track, switches, and cross track.

blue points

blue cross track

Gray Era (1980 - 1991)

These rails are generally the same as the blue rails aside from the new gray color.

straight gray rails

The sleepers were moved closer together (3 per section rather than 2), and they were changed to a specialized part to improve the strength of the connection. Here's what the sleepers look like:

gray era sleepers

The trains of this era were still either powered by 4.5V batteries or the 12V conducting rails.

9V Era (1991 - 2006)

The 9V era completely changed the track components, and did away with the old 4.5V and 12V voltages. Rails sections were a single piece, and they were all conducting.

9V straight rails

RC / Power Functions Era

In 2006, LEGO switched back to non-conducting rails with roughly the same mold as the 9V track. Trains are now all battery powered under either the RC or currently the Power Functions systems.

RC Track

This era included the first and only crossover switch:


It also introduced flexible track:

flex track

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What's the part number for that crossover switch? I've never seen it, is it still available? – SQB Feb 24 '14 at 13:48
Found it, it's in 7996 – SQB Feb 24 '14 at 13:53
@SQB: It is but very expensive (least expensive is over $160). I like it too but it is better to buy two sets of 7895 for $32. – Farhan Feb 25 '14 at 20:30

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