@TrafficEng and
@zambono -- we are now seeing some symptoms that appear to indicate why the car suddenly slowing down on a divided, limited access road is taking place. One theory is that the AP is now reacting to what it perceives as a stopped vehicle or object in the adjacent lane, slowing the car to around 50mph. It may well be that the AP is treating the toll-booth and the bridge support leg as a stopped vehicle in the adjacent lane thus triggering the slowdown until it is past the object and then considering things "all clear."
As we have no release notes or explanation from Tesla, none of us know for sure, but I would encourage you to report these incidents as possible bugs. Assuming the "stopped vehicle in an adjacent lane" trigger HAS been deliberately added to AP software, they clearly need to distinguish that from a bridge support or other fixed object where there is no expectation a passing vehicle should slow down.
I think it is far more likely that what you are seeing is NOT a bug in the software but rather the software is doing what it is programmed to do, but the software isn't compensating/disregarding the bridge support. In systems terms, we have a valid detection (the bridge support for example) but the system is failing to identify it as such (or rather identifying it as a stopped vehicle) and thus triggering the "stopped vehicle in adjacent lane" logic. That makes more sense to me than that the AP is randomly doing this....
it would be interesting to see if you consistently are getting this when passing objects of this type.