This isn't a system to detect if there are cars at an intersection. Wire loops and other systems already can and do measure cars like that.

This is a system to detect "in 32 minutes, twenty-five cars will come from the south, crossing sixteen cars from the east. By pausing the western traffic lights for three seconds, both streams of cars can drive past each other without clogging up the main intersection".

Users don't need to press buttons on apps, they're just using their existing navigation apps which are already providing them with directions (or in the case of Flitsmeister, speed cameras). Similar apps also exist for pedestrians and bikes in my country. My biking experience certainly has improved by having lights on empty/near empty intersections automatically turn green when I'm approaching.

I'd rather see more roundabouts rather than the badly scheduled traffic light system my city has, but the system works for me.

There's the ever-present privacy threat of sharing your (aggregate) location, of course, but in this case we're talking about the government, which pretty much has a live map of what phones are moving where already.