Unless the new GO 95 has changed things, operations like the Muni can have 17' trolley wire because all they run are streetcars; i.e. grandfathering not necessary. When you start getting involved with moving freight cars, then the 22 1/2' (or is it 23'?) standard kicks in. After WWII, the PUC made the Key System raise the height of the trolley wire from 19' because the SN was still operating freight there. They didn't make the Key raise the wire elsewhere, except for perhaps Poplar Street.