Despite having all the necessary equipment for positive train control (PTC) operation installed between Everett and Tacoma, the safety system is not fully operational on all Sounder trips, Sound Transit said Wednesday.

In a letter to boardmembers, CEO Peter Rogoff said that currently, due to technical issues associated with new deployments, only about 56% of trips operate under PTC.

PTC technology requires the installation of wayside equipment along the track as well as onboard locomotives, monitored by a back-office system. In the letter, Rogoff said Sound Transit, which owns the stretch of track from Tacoma to DuPont where Monday’s incident occurred, has already installed all wayside PTC equipment and all Sounder locomotives are equipped with PTC hardware. According to Rogoff, BNSF has also fully installed and activated PTC along the section of track from Tacoma to Everett. BNSF also handles Sound Transit’s PTC back-office system at its control center in Texas.

“Before PTC is operational on a given segment all of these equipment systems must communicate with each other seamlessly following complex configuration work and the completion of testing,” Rogoff said in the letter.

He told boardmembers “the system can actively and automatically control a train if an engineer fails to adhere to operating parameters such as speed limits.”

PTC has been fully implemented on over 15,000 miles of track in the United States, according to the Association of American Railroads (AAR). The system can prevent derailments caused by excessive speed, a potential factor in Monday’s deadly derailment of an Amtrak Cascades train.

Rogoff said that, according to the American Public Transportation Association, of the 41 rail operators required to implement PTC by the 2018 deadline, Sound Transit is one of only 12 that have already installed all of the necessary equipment. But only two commuter rail agencies are fully certified for PTC operations: SEPTA in Philadelphia and Metrolink in Los Angeles.

“While a small handful of agencies are ahead of us, we are ahead of easily two-thirds of our peers and are working diligently to implement PTC ahead of the federal deadline,” Rogoff said.

“There are multiple players here, it’s not something that Sound Transit can do by itself,” he added.

According to The Seattle Times, Amtrak locomotives don’t yet employ PTC in the area where the crash occurred.

Sound Transit expects PTC integration to be completed by the second quarter of 2018, but “implementation steps with other agencies mean that we will not control the exact date of full PTC activation.”

“It is a partnership that requires the effort of all agencies to get the technology fully employed,” Rogoff said.