These are ride safe lights! They have been around out east for a long time and are slowly making their way to the Midwest.
How they work: You install the lights on your sled (there is a company that sells as one unit to install) or you can install them yourself. Yellow(amber) is for all riders except the last one in your group. Green is used by the last rider. You install both colors on every sled if you don’t purchase the single unit. This is so when on coming traffic is coming they can see that there are more sleds coming until they get to the green. They will now know that was the last person in your group. No more hand signaling. This allows for riders to keep both hand on the handle bars at all times.