The name of the signal you describe is “Slow Clear” and the indication is “Proceed at Slow Speed (15 MPH) until entire train clears all interlocking or spring switches, then proceed at Normal Speed.” Normal speed is defined as, “The maximum authorized speed.” The maximum authorized speed would be found in the NS Dearborn Division employee’s timetable, which used to be 70 MPH for Passenger trains on either #1 or #2 track at this location. In the hierarchy of rules Operations Bulletins supersede the ETT, and Mandatory Directives supersede Operations Bulletins.
The speed for the curve at CP482 would be listed in Amtrak’s employee timetable for that area and there would also be a hierarchy of rules there as well.
The “Green” signal aspect west of Porter is "Clear, " which indicates "Proceed not exceeding Normal Speed.
RS