Thinking of or local college. I presume most of the local roads are public roads. There is one block that is blocked off with bollards... so perhaps maintained by the university. Other streets have lane restrictions and etc. I can imagine being asked to move on, but I'm not sure they would be able to kick a person off of the roads.
Then a bunch of sidewalks.
The sidewalks are good for riding slow, and would be inappropriate for doing intervals.
A few of the sidewalks that I rode on 20+ years ago now have signs... NO BICYCLES. I've still ridden on them, and have seen others riding... but ride with caution, and 100% yield to pedestrians, and hopefully nobody will chase you down.
I think PSU in Portland is the same. Some of what should be roads converted to street-width sidewalks, and NO BICYCLE signs on the main campus (often about a block of prohibited sidewalks to get to bike racks).
Now the local community college. That might be a good place to race. But, alas, I think once one turns off the main road, it is all college property. I bet one could easily make a mile loop around the parking lots.
If most of the classes are Monday through Friday, I bet one could circle some of the parking lots on the weekend and nobody would care. But, I'd certainly be careful of becoming a nuisance during school hours.
The football stadium parking lot can be a hive of activity. But, perhaps there are off-hours. Mall parking lot? Unfortunately with holidays and winter daylight times, there might not be a lot of time when the lot would be bright enough to ride without customers, but perhaps an hour or so in the mornings. Again, riding with courtesy.
Fortunately I live on effectively a dead-end road. So, I've created a couple of STRAVA segments. One short hill climb, and two flatish 1-mile fairly straight shots. And, an 11 mile out and back. I don't think I can hit the speed limit, except perhaps on the descent, but go by a no-nuisance rule. Also, on the hill Strava segment, I made an up and down loop, but was careful in direction to not hit a critical descent stop sign at speed.