>>1316906The (somewhat) recent eBART extension of the BART system uses Stadler GTWs on a standard gauge line which connects to the normal BART.
This was because simply extending the BART was too expensive (electrification plus 5'6 broad gauge), too complicated (difficult to source 5'6 broad gauge) and too slow (can't just use off the shelf parts). Plus, there was the politics of it all. Cheap, fast and easy if the American way.