They are, which is why I called it the usual solution. A lot of trams and subways use too tight curves (which can't really be avoided all the time) but then the

They are, which is why I called it the usual solution. A lot of trams and subways use too tight curves (which can't really be avoided all the time) but then there's the BART which uses cylindrical wheels for no good reason except it's expensive to change now. It's a tricky problem for sure, and I didn't intend to solve it with my comment, just shed some light on what the problem space actually is to people less familiar.