In-roadway warning light system and where it's used to increase safety for pedestrians

One example of their use in Virginia from Traffic Safety Corporation:

Crosswalk Warning Light System Improves Safety for Students at Virginia Tech University
The four-lane road running through Virginia Tech University in Blacksburg, VA presented a safety challenge to the University. Use of a traffic signal was out of the question because the site didn't meet necessary requirements. A ten-light crosswalk lighting system from TSC provided the perfect solution to improving student safety.

Thanks to Carol for the tip.