Last December's Amtrak derailment near DuPont, Washington, did more than cost three people their lives and injure dozens more. It's now becoming apparent that it set back regional train service expansion by years.

The deadly derailment happened on what was to be the first day of more frequent Amtrak service between Seattle and Portland. Washington state was all set to subsidize six daily roundtrips — up from four — using a new, faster bypass route south of Tacoma.

The expanded and then retracted Amtrak Cascades schedule of last December would have had trains leaving both Seattle and Portland every two to three hours throughout the day.

But that increase was quickly rolled back after the crash on the inaugural run on December 18, 2017. Train frequency will stay at the current level even when the bypass reopens next spring, said Washington State Department of Transportation rail spokeswoman Janet Matkin.

"We lost a locomotive and an entire train set in the derailment," she said. "So we don't have enough equipment to add those additional trips right now."

Amtrak promised to replace the wrecked train soon after the accident, but the railroad and the state of Washington have yet to agree on how.

"Amtrak is in active discussions with Washington state to determine that best method for replacing the equipment," said Amtrak spokeswoman Olivia Irvin in an email. "Once we determine the best fit, Amtrak will be delivering on that promise."

Matkin said the state would like to get a new Siemens Charger locomotive like the model that was wrecked. For complex industrial equipment such as a locomotive, she noted that considerable time passes between the placing of the order, manufacture and delivery. Washington and Oregon own most of the train sets used in the regional service and contract with Amtrak to operate them.

A letter in a Federal Railroad Administration docket shows that Amtrak offered to replace the wrecked Amtrak Cascades equipment with two similar train sets made by the same manufacturer, Spanish train maker Talgo. Those train cars, now in storage in Indiana, were originally ordered by the state of Wisconsin nearly a decade ago for planned high-speed rail service that was later shelved.

Matkin said the number of unresolved variables in play make it impossible to predict when the long-desired service expansion on the Amtrak Cascades corridor could happen.

"There are a lot of 'I don't knows,'" she said Monday.