Testing is set to begin along Amtrak Cascades tracks where positive train control technology has been implemented, the Washington State Department of Transportation said this week.

That includes the Point Defiance Bypass, the stretch of track that was being used for the first time when a train derailed in December, sending cars dangling over I-5 and killing three people. The train, which was going nearly 80 miles per hour when it derailed, could have avoided derailing had PTC been in operation, federal investigators said.

Point Defiance Bypass.

The state department of transportation said then that Amtrak trains would not return to the bypass until PTC was implemented; it will be required for all tracks on which Amtrak operates by the end of the year.

In a news release this week, WSDOT said track work was “progressing well,” and is a collaborative effort among Amtrak, WSDOT, Sound Transit, and Burlington Northern Santa Fe.

Three major steps must be completed before the tracks are ready for regular Amtrak service, according to the release. Trackside equipment must be installed and operate properly; vehicles must undergo final testing and approval; and BNSF and Amtrak must install back office servers to integrate their systems together. All three are in progress.

Trains will travel along the bypass regularly throughout the summer at up to 79 miles per hour as system mechanisms and train employees are tested. Also during the summer, the release said, transportation officials will host meetings and attend local events to discuss the matter with the community.

Amtrak trains will return to the bypass when testing has finished and PTC is fully active. That is likely to occur in the fall, ahead of the Dec. 31 federal deadline, according to the release, though no date has been set.