[midoridensha]

Great post. Another point is that the DC metro system also uses a non-standard rail gauge: it's 1/4 inch smaller than standard US gauge for some dumb reason, so of course this makes it more expensive to buy cars. Getting new cars made only happens once a decade or so, and involves getting a big juicy contract, and a whole new assembly plant built in the US somewhere.

Here in Japan, the metro system is great. Trains are always on time, they don't break down (because they actually do maintenance!), there's constantly new construction too. On top of this, the train systems are all privately owned: different companies own the different lines. Even so, they all use the same payment method: a simple contactless debit card (suica or pasmo) that works at every station across the country (as well as in vending machines, restaurants, taxis, and countless other places). It's really amazing just how horrible metro systems in the US are compared to this; it's like going to another planet.

[coldacid]

Generally, you'll find that these non-standard gauges for urban/light rail have good reasons, at least good for the time the decisions about them were made. The history of the TTC gauge used here in Toronto is a great example of that.