On the shroud over each light, a number of LED/photodiode pairs should be placed. The LED can be blinked every few seconds. The photodiode will detect significanly more light during the blink if there is snow packed into the shroud. If the controller detects packed snow it turns on a heater to melt it. Similar LED/photodiode pairs are used to detect paper in copiers and other similar situations.
Even though this may sound complex, the parts required are cheap, especially compared to the cost of the traffic light as a whole.
Of the ~40000 traffic fatalities in the US each year perhaps 0.01% are due to this problem, but the fix is easy.
Even though this may sound complex, the parts required are cheap, especially compared to the cost of the traffic light as a whole.
Of the ~40000 traffic fatalities in the US each year perhaps 0.01% are due to this problem, but the fix is easy.