Designing devices to cope with failure requires a different mindset. As Andy mentions - 'it's solid state!' - but its usually something else that causes the failure. The initial hurdle for led replacements was the initial cost, until people figured out they would actually save money in the long run. Unfortunatley, they want them cheaper - so you get a single sided board with a number of leds and some big dropper resistors - all soldered by a wave solder process so you get a very small solder fillet just ready to ceack and fail from temperature and vibration. I dare say the manufacturers are starting to learn about the failures and maybe in the next generation they'll attend to the problems.

With all the maintenance savings acheived, adding a gsm module with even some rudimentry current sensing circuitry, the traffic light could ET Phone Home when it does begin to fail.

There was a post recently on what the poster's company could make. I think I just described a product.