Red means stop, green means go, yellow means…?

I went through a yellow light today. I'd glanced away at the wrong moment, looked up to see the light had gone yellow, and realized I couldn't stop without slamming on the brakes and probably skidding into the intersection.

Later, I was crossing a street downtown when a van went through the yellow in front of me. It looked to me like the driver had plenty of time to stop—but no doubt he had his own excuse.

It's a rare driver who doesn't run through a yellow light on occasion, and in most cases ...