I think this is more concerning for the Secret Service than Waymo.

I would be shocked if Waymo doesn't start avoiding motorcade routes preemptively just to prevent this headline from ever occurring again. They're extremely sensitive to bad PR given the nature of the industry.

I think part of the issue is those routes are somewhat unknown ahead of time?

The SS can and does make that information available when necessary, for instance to private toll bridge operators. Waymo doesn't need significant advance notice either, just minutes for normal vehicles.

I suspect the easiest thing would be a "return to base and shutdown" button that the Secret Service could trigger at short notice - would cause problems for everything wanting to use a Waymo, but I suspect the SS are quite OK with causing disruption already.

Sounds like fake movie spy shit to me. It turns out, the Secret Service is an organization of humans with ordinary lives and a relatively modest budget.

I imagine the Secret Service is considering some kind of routing override for those vehicles.

It’s called the “tow truck protocol”. The specifics are too complicated to get into here, but it involves a phone call, and sometimes they bring in an outside agency known only as “AAA”.