I started my business (https://roadometry.com) to solve this problem. In my opinion, the main issue is the lack of good measurement systems for traffic; most cities only monitor a small fraction of their traffic in real-time.

To waste less time at traffic signals, we really need something more like a vision-based system at every controlled intersection. Then timing can be coordinated on a second-by-second level rather than simply re-tuning every few months, or relying on very rough heuristics.

My system currently requires a desktop with a high-end GPU, but I'm looking at different options for porting this to a low-power architecture for a solar installation.