[idbehold]

If yellow lights all had a fixed duration I would agree with you, but unfortunately the length of yellow lights is variable. Additionally yellow lights have no legal rules behind them. They don't mean "slow down", they are simply an indication that the light will be red soon. You are within your rights to accelerate through a yellow light (assuming you're still under the speed limit).

[janzer]

At least in Michigan yellow lights certainly have legal rules enforcing them, from MCL 257.612 (b):

    If the signal exhibits a steady yellow indication, vehicular traffic facing the signal shall stop before entering the nearest crosswalk at the intersection or at a limit line when marked, but if the stop cannot be made in safety, a vehicle may be driven cautiously through the intersection.

And I know of at least one case of someone getting a ticket, challenging it in court and losing after failing to stop for the yellow light.

Edit: Found the relevant Illinois law 625 ILCS 5 Sec. 11-306 (a)1.:

   Vehicular traffic facing a steady circular yellow or yellow arrow signal is thereby warned that the related green movement is being terminated or that a red indication will be exhibited immediately thereafter.

So still legally defined but it seems in Illinois the yellow is simply a warning signal and does not include a requirement to stop.

[ams6110]

Yellow legally means "do not enter the intersection if you can safely stop" where I live. Of course that involves a judgement on the part of the driver. The duration of the yellow is generally based on the distance across the intersection and allowing cars to clear from inside the "safe stopping" distance.

[differentView]

There needs to be countdown timers on all traffic lights.

[seanmcdirmid]

If you can see the pedestrian crossing light, they usually have countdowns to yellow at least. I use these a lot to estimate the staleness of a green light.

Many traffic lights in China have countdown timers.

[falcolas]

I've attempted this, but if the car which triggered the light change clears the intersection in a particular time (say, with a right turn), the countdown completes only to go back to a "walk" signal.

Makes for some confusing signaling; but it's better than a red light for an empty crosswalk and cross street..

[seanmcdirmid]

On the busy intersections I'm used to, this never happens.

[eli]

Strongly disagree. A reasonable grace period of under a second seems much safer.

[iaw]

Your internet sarcasm is strong.

[eli]

http://blogs.lse.ac.uk/usappblog/2014/03/04/countdown-signal...

[dahdum]

They'll also adjust the yellow light period down to the legal minimum when installing red light cameras, so every other intersection might have a longer yellow around it.