I drive from Texas to Florida to visit my mom and along I-10 I see solar panels on the side of the highway.  Not talking about the solar farms but the single large panels going down to a box on the ground.  

Does anyone know what those are for?

DOT has cameras, speed monitoring stuff, message boards, water level monitors and a host of other stuff that may have some solar power options. They even had radar detector activators in the old days. Some areas may not be served with traditional power grids or the cost of pulling off a high power line to a transformer to the equipment is not cost effective.My guess on your verbal description of the device.

FDOT solar connectors