> But a citywide blackout isn’t that uncommon.

I think too many people talk past each other when they use the word common, especially when talking about car trips.

A blackout (doesn't have to be citywide) may not be periodic but it's certainly frequent with a frequency above 1 per year.

Many people say "common" meaning "frequent", and many people say "common" meaning "periodic".

Even among people who mean "common" as in "frequent", they aren't necessarily talking about the same frequency. That's why online communication is tricky!