It seems strange that all the "solutions"---heating coils, diodes, whatever---seem to presume that the basic form factor of the light system would remain unchan

It seems strange that all the "solutions"---heating coils, diodes, whatever---seem to presume that the basic form factor of the light system would remain unchanged. But wouldn't it be easier to solve if you just rethought the shape of things? Instead of a three-light assembly with hoods over each light (where snow can build up on top of the hood for the next lower light), just reshape the traffic signal as a box with the lights on the back, the four sides opaque (to block glare and peripheral view), and the front side transparent plastic of some variety? There are surely engineering issues there too (like preventing glare off the clear plastic), but it seems like a more stable system, no worries about snow accumulation, and it's probably cheaper to manufacture too.