It's also a serious consideration for companies working on self-driving cars, as unprotected left turns are extremely difficult for the robots.

Not too surprising if we think about it. At a significant number of unprotected lefts at busy intersections, you basically have to semi-aggressively pull out in front of oncoming traffic and rely on them to slow down for you in order to get through in a reasonable time. It's tough to automate that in a safe way. Especially if it involves fuzzy value judgements about whether those cars seem like they'll probably slow down for you.

Would be a great navigation mode for maps apps to add. No left turn or easy driving mode. If ups does it, why not others?

That should just be the default routing unless it's absolutely unavoidable.

I think I read an article like this on HN a few months ago, ty for the share