Standard "heavy rail" Amtrak (think: Pacific Surfliner, two stories tall with thundering diesel, https://www.pacificsurfliner.com/plan-your-trip/ ) can run at 120 MPH if the track has positive track control. By some definitions that makes it "high speed rail" heh.

Which the Surfliner didn't in my day (and I think it still doesn't) - but it would hit 90 MPH through Camp Pendleton and I swear my GPS clocked it at 100 once.

Still would beat a car LA station to San Diego station during rush hour traffic.

Freight priorities on rail don't apply in the Northeast Corridor, almost the entire stretch is owned by Amtrak (unlike the rest of the US). Acela and NE Regional have the right of way up here (with preference given to Acela). The reason it's slow is because the tracks are old and aren't rated for high speeds. They were constructed with sharp(ish) turns during an era of much slower trains which entirely precludes Acela from going 300km/h (like TGV), and only allow for ~240km/h on a tiny stretch between Boston and Providence, and a handful of small stretches between NYC and DC.

Despite many claims that Acela is swift, the killer argument is looking at the time difference between Acela scheduled time vs regular trains with only a few stops on the same route.

I happily pay more for Acela because the carriages are more comfortable but if the time is inconvenient I am happy to book a regular train.