It's some kind of awful compromise to allow more car traffic because it's less disruptive than a full four-way signal. Except it seems to have added a lot of behaviors that drivers don't expect or pay attention to.

In isolation, the lighting modes make sense. A solid red is always stop. A flashing red is equivalent to a stop sign. The yellows means changing to red. Confusingly, the lack of a green seems to be an issue because drivers misinterpret that to mean the light is inoperable or can be ignored.

It seems like the issue is related to stroads, where drivers only look for green and red lights, and nothing else:

> The researchers also found that the type of roadway impacted how drivers interacted with the beacon. On four-lane roads, there was less premature stopping, but also lower rates of stopping during the red-light phases: 29% drove through the solid red and 69% drove through flashing red. [...] Driver performance for correctly stopping during the solid red phase was best at urban, two-lane roads: only 11% of drivers failed to stop. There was still some stopping confusion in the other phases, but generally more compliant than other sites.