49 USC 20502 – Requirements for installation and use
(a)
(2) A railroad carrier ordered under paragraph (1) of this subsection to install a signal system on one part of its railroad line may not be held negligent for not installing the system on any part of its line that was not included in the order. If an accident or incident occurs on a part of the line on which the signal system was not required to be installed and was not installed, the use of the system on another part of the line may not be considered in a civil action brought because of the accident or incident.
(b)
(1) may be operated safely without unnecessary risk of personal injury; and
(2) has been inspected and can meet any test prescribed under this chapter.