Pennsylvania streetcars do not run on standard-gauge track. This is not just a local quirk: it was a law of the Commonwealth. Streetcar companies must not lay standard-gauge track. Why did we have such a law? Well…
This is Liberty Avenue in 1889, where a railroad ran down the middle to serve the wholesalers. Now imagine one backroom deal with the streetcar company, one little switch, a few extra feet of track, and suddenly the Pennsylvania Railroad has access to every major street in the city.
But that can’t happen, because the streetcar tracks are a different gauge.
That is why, to this day, streetcars in Pittsburgh and Philadelphia use Pennsylvania Broad Gauge or Pennsylvania Trolley Gauge, 5 feet 2½ inches, instead of the standard American rail gauge of 4 feet 8½ inches. (Actually, Philadelphia is off by a quarter-inch at 5 feet 2¼ inches.) Most other American transit systems use standard gauge, although New Orleans streetcars use Pennsylvania Broad Gauge, too.
