In the US, Amtrak (the national passenger rail service) operates a big 25Hz single-phase system, dating to the 1920s, for traction power between Washington DC and New York City, and between Philadelphia and Harrisburg, PA. It includes two dedicated 25Hz hydroelectric generators at Safe Harbor Dam on the Susquehanna River, motor-generator frequency converters in PA and NJ, and more recently, solid-state cycloconverters
See:
Amtrak 25Hz traction power system
