[onmai-xyz]

Yellow could be used to start the sequence in reverse order. You are stopped at an intersection with a red light, light turns yellow for a brief time indicating proceed with caution as the cross street has just had its green light go directly to red. The brief yellow turns green allowing cautious transition of cross traffic right of way, instead of the regular use of yellow which seems to induce a lack of clarity on what to do, accelerate or decelerate. Green directly to red makes it very clear what to do, stop or maintain velocity. The grey zone still exists but it is on the new flow to proceed with caution instead of just, green=go. Rightly this would be rejected as it wacky, but wow t-boned accidents are horrendous and people really like to game the yellow light in a reckless way. How can we move towards caution.

[Swizec]

In Europe lights go from red to red + yellow to green and from green to yellow to red. That’s how you know which yellow it is.

And at least in theory just yellow does mean “proceed with caution”. You have intersections without a green light, just flashing yellow.