The former Pennsylvania Railroad section of the Northeast Corridor is electrified with 11,000 volt 25 Hz, as are the former Reading commuter lines. I need to check the historical basis for the lower frequency. Apparently it was a combination of transmission losses, and being able to operate “universl motors” that could operate on DC.
The 17 Hz is actually 16 2/3 Hz of the Deutsche Bahn (1/3 of 50 Hz).
Those are old legacy systems
In 1997, I read Michael Bezilla's The Electrification of the Pennsylvania Railroad, and now it's out of print. I was going from a failing memory.
Yeah that’s mostly my understanding (see previous post.) With AC you could mitigate the huge transmission loss you get with direct current, but as you increased the frequency you start to have higher and higher inductance losses in the windings of a DC motor. 60 Hz was too high for those motors. 25 Hz was a trade-off point between internal losses and line losses.