I see there was a lot of interest in power distribution. There's an
excellent book that covers the history of electric propulsion on steam
railroads, "When the Steam Railroads Electrified" by William
Middleton. It is now in its second edition which contains added
information. There's a chapter on motor technology.
Railroads electrified to (1) increase track capacity since electric
trains were faster and more flexible, and (2) avoid smoke in tunnels.
A big innovation was the "multiple unit" (MU) passenger train. These
are trains, usually commuter trains or subways, that have no
locomotive. The motors are part of the carriage with the wheels and
the engineer sits in a vestibule at the front of the train. These
have the advantage of being very flexible in size--one car or 16 cars
as needed, and easy to turn around since they are bi-direction. MU
cars also accelerate faster.
With the advent of diesel engines and improved ventilation, some
tunnel electrifications were shutdown. Some commuter electrifications
were shut down as well.
The Pennsylvania Railroad had a massive electrified network for its
passenger and freight trains. While started in 1915, it reached its
peak in the 1930s. Most of the passenger network remains in place run
by commuter agencies or Amtrak, but the freight network was shutdown
after Conrail inherited the Pennsy.
Diesel locomotives are actually electric, with the generator carried
above. As such, they have many of the advantages of an electric
engine without the expense of maintaining a power distribution network
(substations and overhead wires).
Street railways and subway-elevated lines used 600 V DC and most still
do (somewhat higher voltage) to this day. The relatively low voltage
requires frequent substations.
Railroad trains used a variety of voltages and AC frequencies. As
mentioned, 11000V 25Hz was common and still in use to this day.
I am a strong proponent of electric propulsion. A modern electric
powerhouse is far more efficient due to economy of scale than an
on-board power plant could ever be. The plant could run on coal, oil,
or gas, and many can be switched from one source to another. The
exhaust can be economically cleaned up by scrubbers. Since the plant
is more efficient in the first place, more of the fuel is burned up
and less left over to go up the stack. Also, nuclear plants which do
not release air pollutants or use scarce oil can be used.
Rail is the most efficient means of travel for short distances.
Unfortunately, this country has chosen to massively invest in air and
highway and despite that investment, those modes remain overcrowded
and unable to accomodate all demand. Fast trains -- which are not
that costly to build -- should be used for regional transport needs
and would be far more efficient in terms of fuel, safety, and
pollution. We don't have the land to build more airports and roads,
and trains fit in anywhere. Planes are better for coast to coast