The result of clear "traveler" beer bottles post drinking on long car trips. Especially evident around large signs displaying distances to locations (or "score boards") and can range in sizes from near full bottles to absolute dust depending on variables such as local speed limits, build quality of road furniture and skill level / level of intoxication of bottle ejector.
Road Emeralds - green bottles
Road Rubys - brown bottles
Broc -"This is a work car, don't just throw bottles on the floor!"
Fish - "Time to make some Road Diamonds!"