[jfim]

They're not typically used for passenger cars, but semi truck drivers and first responders use them since they're visible from farther away in both regular and low visibility situations like fog, rain, and at night.

[Kuinox]

They are not used in europe. The first time I saw one was in Japan last week.

We have portable triangle reflector in Europe that are in every truck or car.

[throwup238]

Consumer vehicle emergency kits used to come with them decades ago. Now they come with plastic reflectors or LED beacons.