After the [[Downers Grove train wreck (1947)|1947 Downers Grove train wreck]] caused by a missed signal, the ICC required additional technical safety systems for any train traveling at or above 80 mph with the rule taking effect in 1951. Those railroads still interested in high speed operations IIATS met the minimum ICC requirements with a loser cost compared to [[Pulse code cab signaling|other cab signaling]] or automatic train control systems, however with rail travel facing increased competition from cars and airplanes most railroads simply choose to accept the new speed limit. Only the [[Atchison, Topeka and Santa Fe]] choose to fully equip its Chicago to Los Angeles and Los Angeles to San Diego main lines in support of the [[Super Chief]] and other premier high speed trains.
WithIISAT installations reached their peak in 1954 with a total of 8650 road miles, 14400 track miles, and 3850 locomotives equipped with the system. However, with the collapse of long distance passenger rail travel and the general North American railroad industry malaise in 1971, the bankrupt [[Penn Central]] was permitted to remove IIATS from its Water Level Route along with the Southern and other railroads with test or pilot IIATS systems. Even the ATSF and successor [[BNSF]] were gradually allowed by regulators to remove IIATS from parts of previously equipped lines due to the reduced passenger traffic. At the turn of the 20th century the only IIATS equipped lines were the [[Metrolink (Southern California)|MetroLink]] and [[Coaster (commuter rail)|Coaster]] line between San Diego and Fullerton,<ref name="look at" /> parts of the former ATSF Super Chief route in California, Arizona, New Mexico, Colorado, Kansas and Missouri and the former [[Chicago and North Western Railway]] [[Union Pacific North Line|North Line]], [[Union Pacific Northwest Line|Northwest Line]] out of Chicago operated by [[Union Pacific]] on behalf of [[Metra]]
In 2001 a new IIATS system on the [[New Jersey Transit]] [[RiverLINE]]. This is a light rail systems running on shared track with main line freight traffic and IIATS is used to enforce a full stop at equipped signals instead of as a warning system.
