As for the first question, a correct answer, but not the one you probably are looking for, are all the bridges on the IC suburban between Central Station, Roosevelt Avenue, 12th Street Chicago and Kensington Junction, where the IC tracks themselves are still used by the last of the Insull interurbans, the South Shore, which certainly was an interurban, if now regarded as a suburban railroad. I would assume that there is at least one major bridge on that line, over a river or canal, not just street overpasses. I IC suburban is an electrified steam operation.
But possiblyi at one point the Washington, Baltimore, and Anapolis did share a bridge with the PRR for the short time it contiued to operate into Washington after the PRR electrified to Patomic Yard and Washington Union Station. I know there was a grade crossing between the two, and they may have shared a bridge with separate tracks.
But should the East Bay suburban operations of the Southern Pacific, reorganized as the Interurban Electric, be considered as electrified steam, since the SP did provide some suburban passenger service to the East Bay before electrification? There was a major bridge leading to the SP Oakland Mole, electrified for the SP’s Interurban Electric suburban service, and at varying times both Key and SN ran there, even though Key later had its own terminal. The SF Oakland Bay Bridge is not in the runing since the tracks were always electric, with two systems.
The Daisy Line was the interurban that connected Louisville, Kentucky, with New Albany, and possibly Jefforsonville and other points in Indiana. It was a broad-gauge operation with equpiment compatible with the Louisville Streetcar system, and it use a stanard guage steam railroad to reach Indiana, sharing one rail over the bridge. I think it was the Big Four of the NYC system, but it may have been the Monon.
Tbe Indiana Railroad may have used the same