Traffic lightning must be visible at a distance in all weather conditions. This requires high luminous intensity, high colour temperature and very long service life.
Incandescent lamps meet these demands and have been used in traffic signals for more than 80 years. On top of this incandescent lamps are cheaper in purchase and easy to change. Last but not least the light bulb gives off heat and thereby prevents snow piles and dew on the traffic lamps. The light bulb is the safe choice.