What I mean is, light rail systems that use a linear induction motor pulling on a center “reaction rail”. See this Wikipedia page for what I’m talking about. So we have the Innovia Metro, now owned by Bombardier (the tech behind the Vancouver SkyTrain), and Japan also has their own very similar linear metro system, which are deployed in a few of their cities, notably Osaka, and was also exported to Guangzhou, China.

The tech originates in the 60s and 70s, and it’s not that complicated: an aluminum center rail couples with a linear induction motor on the train, which generates the movement along the tracks. It’s used for both accelerating and braking the trains, with the mechanical brakes only used in an emergency. It’s something you can fairly easily build a small scale of at home as a DIY project, and many people have.

According to TransLink in Vancouver, the motor components almost never breaks down, they’ve claimed in one video that they’ve never had to rebuild or replace a linear induction motor, with no gearbox or transmission to break down either. And the center rail is completely passive, literally just a sheet of metal, and since the motor never touches it, there’s really no reason for it to experience much wear. Therefore, I imagine the trains need way less maintenance compared to trains with rotary motors. I live in Vancouver, and we still have tons of the first generation trainsets from the 70s that have lasted until now and show no sign of giving up the ghost anytime soon, and the system isn’t even bothered when a section of center rail is completely missing, there’s been a two meter long gap in the center rail for months, and only got fixed recently, with none of the trains having any problems with it. I couldn’t find much info about the Japanese system, namely because I can’t read Japanese, but I imagine it’s similarly reliable.

There are also a lot of benefits, namely, acceleration and traction (or, disregard for the lack of it). I ride both the Canada Line in Vancouver and the rest of the Skytrain system a lot, and you can really tell the difference in acceleration. The Canada Line, which uses regular motors and disk brakes, definitely takes a lot longer to get up to speed, and seems to take even longer to stop while entering a station. You can actually feel a pretty significant difference in acceleration and especially braking just based on how much you’re shifted forward and backward. Also, since the contact area with the running rails isn’t really relevant to making the train move or stop, it can handle low traction without losing performance (or more importantly, braking power). And I’ve read accounts that Vancouver chose the linear induction system specifically because it’s mountainous, and they were worried about trains losing traction on hills when the tracks are wet or iced over, and the Skytrain does have some pretty steep gradients, despite being mostly elevated.

I feel like those benefits would make it really good for urban rail, where you have frequent starts and stops so getting up to track speed faster can actually save on travel time, and you have less options for going around steep hills while still connecting important locations.

Actually, I can see this being even more useful as surface level light rail or trams/streetcars than elevated rail, because in that case you really do have to go along the slope of hills, and better acceleration and especially braking is even more important when you have to deal with cars, bikes, and pedestrians. Third rail wouldn’t work in that case, but there’s no reason this tech can’t work with overhead lines or batteries. Hell, even diesel-electric. You can even run regular trains on the same tracks or upgrade existing tracks while keeping old rolling stock because the center rail doesn’t stick out above the running rails.

I’m not sure what the energy efficiencies are in terms of both driving the train and regenerative braking, but I imagine it’s less than a regular motor simply because the magnetic fields are less confined, (so some of that magnetic energy dissipates). Maybe that’s actually a massive drawback and it’s, like, a quarter of the efficiency or something? Any electrical engineers able to enlighten me?

So, why aren’t linear induction based light rail more common? I find it kind of weird that this kind of tech hasn’t received that much adoption, and especially that there aren’t any other companies trying to make a similar system, or making competing trains that can run on the Innovia or Japanese tracks. I’d love to hear what your thoughts are on this.