The North County Transit District, or NCTD, is now testing Positive Train Control along its San Diego subdivision.  NCTD authorities expect the trial operation period to run through September, and warn some passengers may experience train delays.

The coastal rail suspended service intermittently in May 2015 for PTC installation. Charlie Neuman/Union Tribune.

Trains could also come to a brief stop based on PTC automatically applying the brakes.   .

Metrolink is the first commuter rail in the United States to operate PTC across its entire railroad system.   In the Rail Safety Improvement Act of 2008, penned just after the 2008 Metrolink Chatsworth crash, Congress formally ordered the rail industry to implement PTC across more than 60,000 route miles of train tracks.

The NCTD got off to a late start in installing PTC in spring 2015. Congress extended its deadline to December 2018 after most train companies threatened a service shutdown if lawmakers insisted on enforcing its original 2015 deadline.