North American railroad signaling

For the physical signals, see North American railroad signals.

Standards for North American railroad signaling in the United States are issued by the Association of American Railroads (AAR), which is a trade association of the railroads of Canada, the US, and Mexico. Their system is loosely based on practices developed in the United Kingdom during the early years of railway development. However, North American practice diverged from that of the United Kingdom due to different operating conditions and economic factors between the two regions. In Canada, the Canadian Rail Operating Rules (CROR) are approved by the Minister of Transport under the authority of the Railway Safety Act. Each railway company or transit authority in Canada issues its own CROR rulebook with special instructions peculiar to each individual property. Among the distinctions are:

  • The US has a much longer history of power operation of switches ("points" in UK parlance) and signals.
  • The US and Canada departed from UK practice wherein a semaphore blade is devoted to each route (Route Signaling). General North American practice is to group routes by speeds and use a single blade for, say, "medium speed" regardless of the number of routes involved (Speed Signaling). The primary exception to this situation is in the field of heavy rapid transit, such as subways and elevated lines, which make use of a localization of the British practice, or a combination of the AAR and British systems. Some freight railroads also still use route signalling.