Some questions I have on the newly rehabilitated Nisqually Line (Point Defiance, WA bypass)

When driving on Southbound I-5 at Berkley St / Tillicum you can see various signs along the track.

1. P 68 MPH South of the Berkley street crossing about 1/10 of mile
2. P 70 MPH South of the 68 MPH sign 1/10 of a mile.

Why the change of 2 MPH for P trains?

3. a rectangular green sign on metal post, another sign across from the green one, but facing North (can't see the color) This is near the two MPH signs. What is that sign for?

4. North of the Dupont/Steilacoom crossing there is a F 10 MPH sign (facing South). Before the rehab I was told the freight train speed was limited to 10 MPH due to track condition. Are freights going to run faster than 10 mph on the track North of Dupont?
Or, is the speed restriction due to the concrete ties?

I was told by a BNSF employee about 6 months ago that wood ties are more flexible with heavy weight trains such as oil trains etc. Just wondered if the military train movements would be reason for 10 mph

Thanks in advance!