While an interesting idea I don't think WSDOT ever looked at that route.

Other people on here know more about the line but it has a steep grade out of Tacoma, Tacoma Rail has had problems getting trains up the hill in the past...

Plus Tacoma Rail from what I understand sold the portion or is leasing the trackage from Rainier to Centralia/Chehalis to another company that has markings WWR Western WA Railroad. They have used the line for mainly storing flats and oil cars over the last 5 years or so. In fact, they still have flats on the line in Rainier on either side of the bridge over hwy 507.

And from what I've seen now that track speed is 10 mph.

If WSDOT ever did use that trackage, it would take years for them to upgrade. Look how long it took the contractor Stacy Witbeck a long time to rebuild that bypass. I remember talking to BSNF MOW crews and they said they could have done it much quicker

If anyone does know if WSDOT looked at that route, it would interesting to read their report on it.