Yes. I still think it should be added to TM in some form, but not sure about adding it to to usai. The state maintains the freeway and logs it as "route 5S", but like many other Interstate routes Caltrans doesn't internally designate it as an Interstate route. There is no Interstate signage for the route on the I-5 mainline, the only I-5 sign on the spur is an unbannered sign on a "freeway entrance" sign assembly at 5S's east end.
I suggest adding it to usasf as a named Colorado Street freeway (or Colorado Freeway), sidestepping the iffy Interstate signage.
Anyone want to weigh in?