Sitting in traffic this morning on my way to work, I was wondering: Why, in the 21st century, are traffic lights still based on 19th century technology? We have self-driving cars, for heaven's sake, yet each day millions of cars sit in long lines idling their engines, burning gas and spewing carbon into the air, while the cross road is empty.

I'm no engineer, but it seems to me that it would be relatively simple to use GPS, motion detection and other technologies to make traffic lights more efficient, instead of relying on mechanical timers and switches.

Am I missing something here? Or is this just the result of inertia on the part of city planners?