I probably should wait for a more technically accurate answer from BOB2, but I can think of several issues starting with wheel and rail profile. Often streetcar systems use relatively small flanges that fit with the shallow flangeways on streetcar girder rail and switches. These streetcar wheel flanges don't work well with regular railway switches. Regular railway flanges ride up on the streetcar track flangeways. There also are car profile issues. LAMTA light rail cars are relatively narrow and the platforms are built to match. Would the OC streetcars have the same car width, use the same platform heights? It helps me to think about a streetcar system as a large machine with many moving parts, all of which must fit. Another streetcar system may have a similar appearance, but the parts fit together differently.