HOW IT ALL WORKS - All Aboard: The Complete North American Train Travel Guide - page 174

visually displays trackside signals for the engineer. Since most
Amtrak locomotives outside of the Northeast Corridor have not
been so equipped, their speed has been limited to 79 mph.
That is changing however. In 2009, the Federal Railroad
Administration directed that all U.S. railroads begin to imple-
ment a system known as positive train control (PTC). The PTC
technology can, if necessary, automatically override actions by
a train's engineer—if, for example, he or she should fail to stop
before passing a red signal. The new system will be in place on all
trains by 2015. For Amtrak, the net result will be greater safety
and higher speeds where track conditions permit.
This is certainly not to say that many trains don't go faster
than 79 mph today. On the Northeast Corridor between Boston
and Washington, D.C., Amtrak trains routinely travel between
105 and 125 mph, with the high-speed Acelas reaching 150 mph
along a few stretches. In parts of Missouri, Pennsylvania, and a
few other areas, passenger trains travel at 90 mph and higher.
Apart from the speed limits, how fast the train goes depends
on several factors, including track conditions, the weight of the
train (meaning the number of cars), the type and number of loco-
motives pulling the train, and whether that automatic signaling
device has been installed in the engine cab.
Communication
In the old days, members of the train crew communicated among
themselves with visual signals, such as waving their arms or, at
night, lanterns. Today it's all done by handheld radios, linking
the conductors with the crew in the head end. The most powerful
radio on the train is in the locomotive cab, and with it the engi-
neer can communicate with the railroad's dispatcher, who may be
hundreds of miles away. The engineer can also receive radio mes-
sages from the crews of other trains, from Amtrak personnel at