Back up plan not needed
The three-digit telephone number "9-1-1" has been designated as the "Universal Emergency Number," for citizens throughout the United States to request emergency assistance. It is intended as a nationwide telephone number and gives the public fast and easy access to a Public Safety Answering Point (PSAP).
In the United States, the first catalyst for a nationwide emergency telephone number was in 1957, when the National Association of Fire Chiefs recommended use of a single number for reporting fires.
In 1967, the President's Commission on Law Enforcement and Administration of Justice recommended that a "single number should be established" nationwide for reporting emergency situations. The use of different telephone numbers for each type of emergency was determined to be contrary to the purpose of a single, universal number…
https://www.nena.org/general/custom.asp?page=911overviewfacts