In several countries in Europe they occasionally paint markings on the road (chevrons or dots or similar) with a sign like "Keep apart 2 chevrons". Some places have electronic speed limit signs to reduce the maximum speed in heavy traffic, which reduces risk and improves flow.

https://www.alamy.com/stock-photo-keep-apart-2-chevrons-moto...

(Obviously we can't tell the speed of the cars in the photo, but if it's the standard speed many drivers are still ignoring it.)