The 6.9kV is signal power voltage, not the voltage at the signals. The signal power is transmitted for multiple miles along the catenary structures from the various wayside substations. The voltage is similar to the voltage used by utilities for moving distribution power over miles. The 6.9kV power is stepped down at the signal locations to a lower voltage to operate the track circuits and power the signal displays.

Most railroads today simply have the local utility provide power to each signal location. The utilities bring the power to the signal sites at voltages up to 34kV, then step it down to a more common voltage (480, 240) for supply to the signals. The power distribution is utility. The signal system is railroad. Looking at it that way, Amtrak's system is both the power distribution and signal system: both under Amtrak control. It is a legacy of the old Pennsylvania Railroad. One advantage is that it protects Amtrak from signal outrages caused by local utility power disruptions.