Traffic light patterns programmed by morons.
Some examples I got caught in recently.
The cross street is a minor subdivision. In the 2 years I've lived near this intersection, I've never seen more than one or two cars come out of there. But the signal cycles all night. There are times I can get stuck at a red light for no one. Very frustrating. I can barely understand having a signal at all since there are much bigger subdivisions in the area that join the same road with no signals and they seem to handle morning and evening rush hours just fine.
Here you have an entrance to a driveway. There used to be a school there, but now its a field and the driveway is blocked off. Furthermore, the other end of this driveway is not controlled. You'd think they would have taken this light down? Or at least changed it to a 24/7 flashing yellow? Nope, the damn thing still cycles.
Two signals to two subdivisions. Usually they're synced together, but sometimes they're not. How do I know? Because a few nights ago, I got caught at both of them. At 9:45pm. With no other cars in sight.
And there are countless other examples. There are three very obvious solutions to these problems. In order of increased cost/complexity, (1) Set them to flashing yellow/reds at certain hours overnight (2) alter the patterns to have longer greens for main roads in non-peak times or ideally (3) replace them with smart lights that sense traffic flow.
I know it would be a fairly big infrastructure tear-up to replace all traffic lights, but my parent's town did it a few years ago and now I'm spoiled. Its really a fantastic concep. Main road lights remain green until a car is detected on the cross road. Then the light changes to let that car through, and changes back to the main road immediately after. If there are two cars on the cross road, it lets both through and changes back. There's even one intersection where if you want to turn off the main road onto the side road, it will give the oncoming traffic a red to give you a protected green arrow, then switch back. And the best part - the sensors start far enough from the intersection so that you don't need to stop. There were teething problems at first though - motorcycles sometimes weren't detected and riders would have to jump off to press the pedestrian crossing button to get the light to change, so the town did set the cross street to a quick cycle every so often, but that's a very minor delay if any.
Granted, these annoyances are all very first world. Oh no, I have to sit here in my car for an extra two minutes. But I started thinking, how many tons of CO2 are emitted by cars stopping for, idling at and re-accelerating from traffic lights that serve no purpose. I'm willing to bet its a non-negligible amount. And in this age of "environment impact this" and "environment impact that" this seems like a very obvious thing to address.