Patently Apple:

The system relates to improving detectability of road signs and vehicles on the road in low visibility conditions like fog or snow with a plurality of retroreflectors. For instance, if traveling on the road in a snow storm and road signs are covered in snow, a retroreflector system, using radar, would be able to read the text under the snow and relate it to the driver on a CarPlay display and/or other device display.

This is an interesting invention, shows Apple is still going down the Project Titan road, has value for a human driver.

But, it seems to me, the future of road signs and low-visibility hazard warnings (a car stuck in the middle of the roadway in a snowstorm, for example), is digital, not analog. In addition to flashers and reflectors, which are great for humans, signs/on-board hazard signals designed for automated vehicles will be equipped with high speed communications targeted at all nearby traffic.

The rub here is that time in between, where both human and automated traffic share the road.