My last post discussed snow covering LED lights. Its a story that doesn't seem to want to go away.
I came across a low tech solution sold by McCain (a large traffic signal supplier whose products are widely used in Minnesota). Their Scoop Tunnel Visor has a beveled opening that provides air circulation around the LED lights which reduces snow build up. They cost about $20 each (which isn't much of an upcharge if they are being put on new signals instead of the standard visor).
The Colorado DOT has been using the scoop visor and seems to think they work. According to CDOT spokeswoman Mindy Crane - "They've helped immensely in terms of keeping the snow off the traffic lights. It's not high-tech and it's very economical."