National rail network

In United States railroading, the term national rail network refers to the entire network of interconnected standard gauge rail lines in North America. It does not include most subway or light rail lines. Federal Railroad Administration regulations require passenger cars used on the national rail network to be heavy and strong enough to protect riders in case of collision with freight trains. Most mass transit vehicles do not meet this requirement. Commuter rail equipment generally does, as do all Amtrak cars. Mass transit systems that do not meet FRA requirements cannot even be connected to the national rail network, unless the connection layout only permits the transfer of one or two cars at a time, for example via a Y stub siding.