You need to make a left turn, and you come up to an intersection. Cars in the opposite direction have the green light, and are already passing through. In attempts to get a head start when the flow recedes, you edge past the line to stop at. The light turns red, and you have not turned yet.
Was it legal for you to edge out?
Is it legal to make your left turn, to clear out the intersection?
I’m not a lawyer or police person, but I believe that if you have entered the intersection, it is O.K. to complete the turn. To put it another way, when the light turns green for you, you can go forward into the intersection (with your left turn signal on, of course). You are already past the stop line, but that is permitted because you have the green, but you are stopping to yield (as you should) to those going straight in the opposite direction. When the light turns red, you should finish the turn, since the alternative is to stay in the middle of the intersection and obstruct traffic the other way.
However, in many cities, such as New York, where there is the potential for gridlock, you may NOT “block the box” if there is not room for you to get out of the intersection.
It’s legal - or at least accepted in the parts of “flyover country” that I know best (a path from the Great Lakes to the Gulf). There are some intersections where that’s the only way you’re going to be able to make a left turn (no one with budget authority having agreed to the need to spend money to add either a green or a blinking red arrow to the traffic signal there).
I have driven in quite a few more states than that swath I describe above, but not necessarily enough to feel certain about. I know that in some places there’s an actual sign saying “left turn … when traffic clears” Those are more common up north, but my memory is insisting the ellipsis is a replacement for “on red”.
Maybe at least my response will prompt more - including a correction, if my memory is flawed. 
The law in California on this was changed a few years ago. I believe it’s now illegal to enter the intersection for purposes of making a left turn unless you are sure you can clear the intersection before the light turns red.
For example, a car ahead of you enters the intersection planning to turn left but stops to allow oncoming traffic to pass. You shouldn’t enter the intersection until that car has cleared. Then you can go ahead with your turn if the light is still green and through traffic from the other direction permits.
There is also the case where traffic is backed up on the street you want to left-turn into so that you would be stopped in the intersection. You should wait until the backed up traffic clears and there is room for you to turn and completely clear the intersection. If this requires that you miss your chance to turn, tough.
These examples apply to intersections without a separate green left turn arrow.
I live in a relatively small town and I do’t know how strictly that law is enforced here. I would expect that it’s more crucial in cities.
It’s my understanding that this is not only allowed, but encouraged, because if you don’t get out into the intersection, there might never be a gap in the traffic, and you, and all the people behind you, could be waiting for hours.
I’m sure this has been brought up on SDMB before too.
Laws vary by state. I live in California and looked at the California Vehicle Code and Driver Handbook and couldn’t find anything that said it was illegal. It certainly is accepted practice in California. A left-turner who stayed behind the limit line wouldn’t be able to make the turn at all if the oncoming traffic hadn’t cleared by the time the light changed. In fact, it’s considered rude (or oblivious, at least) for a left-turner to stay back before making the turn, as this can prevent other cars from getting through on the same green light (especially if they’re also turning left).
I experience this all the time. On some lights there will be a sign that says “left turn yield on light”. I always pull into the intersection if I can.
More than once I’ve sat behind someone who doesn’t do this, all the while saying to myself “at least pull into the intersection dickwad; now there you go!”
Most states have laws making it illegal to enter an intersection unless it can be cleared. Most folks thinks this applies to those going straight but does apply to those turning left. At a legal forum I visit we get posts from folks that have been cited for running a red light when they have been caught in the intersection while turning left. If I can’t clear an intersection, I will wait at the stop line, I’m not going to risk a ticket just to make a left turn.
When I was visiting my in-laws who live in a small town in Mississippi I noticed an interesting thing. I was the second car in line waiting to turn left at a stop light. The car in front of me pulled into the intersection when the light turned green waiting for a break in traffic so that they could turn left. The light turned yellow, and there was no break in traffic. As the light turned red, and oncoming traffic came to a stop, I expected this car to complete the left turn…I was wrong! The driver put the car in reverse and started to reverse out of the intersection. I had to put my car in reverse quickly to avoid being struck. I had to wait at this intersection through several more light changes until the driver in front of me was actually able to complete their left turn! Each time as the light turned red they would throw their car in reverse and creep back towards me. Honking at them made no difference…no difference at all.
I thought that this must just be one inexperienced driver, but much to my surprise it happened two more times during the week that I was in Mississippi. I don’t know if it is a local thing, or if the traffic laws in Mississippi are different, but I sure was surprised when I saw those reverse lights light up and start coming my way!
I didn’t point out in my above post that there were times when the driver in front of me could have completed a turn before the light turned red. However, a few times while the light was still yellow they would throw the car in reverse and clear the intersection by reversing back towards me. Perhaps Mississippi has a law stating that you can’t clear the intersection if the light is already red or about to turn red, even if you have been waiting in the intersection for a long time…I don’t really know. Since nobody drives like that where I am from, It took my by surprise.
I don’t know for certain but I believe that turning left on red is illegal. However I’ve never known anyone that got a ticket for it and I will do it myself on occassion, even though I consider myself to be a mostly cautious and law-abiding driver. The fact is that at some intersections, during certain times of the day, you will NEVER be able to make a left turn otherwise. It would probably behoove us to get our acts together and petetion the city councils to have arrow lights installed at these intersections instead of putting ourselves in front of possible oncoming ten-ton trucks.
I’ve never seen that. I have seen occasional stupid people wait behind the line during the green though. I honk at them.
I always enter the intersection, and complete the turn when possible, even if the light has turned red.
In Illinois, The Rules of the Road booklet they give out at the DMV specifically said to pull into into the intersection, although this was 18 years ago when I first got my license so I don’t know if it’s still in there.
The key is that you’re not really turning left on red. You’re entering the intersection when you are supposed to, on green, and then finishing up after the light is red.
I watched someone do this the other evening. The photo enforcing stoplight camera thingy took it’s picture as soon as the light turned red and they were still in the intersection.
This question has spurred a flame war in the traffic column of the Washington Post. (Do other cities have traffic so bad that there is a traffic column in the local paper that runs 3-4 times a week?) The columnist, Dr. Gridlock, advocates pulling out on green, because in many situations (heavy traffic, no left turn arrow) that is the only way you will ever get through the intersection. Some readers disagreed, most of them “think inside the box” types who always colored inside the lines when they were kids. It is definitely not illegal in the three DC metro jurisdictions.
However.
When I was in high school in Maryland, a teacher told me that he did this, and when he turned left after the light turned, someone coming straight from the opposite direction ran the red light and hit him. He was held responsible for failing to yield, even though the other guy had run a red light. The red light did not alleviate his obligation to yield to oncoming traffic. That is just one case, not necessarily the law.
Those thingies take two photos. One to show that the light was red before you entered the intersection, and one to show that you actually entered the intersection after it turned red. Need 'em both.
I’ll second the fact that here in California there are many places where this is the only way to make a left turn. Indeed, even so it only amounts to 1 car turning per green-red cycle. If you’re 10 cars back, it may take you 20 minutes to make your turn, but at least it happens. A red light is sometimes the only break in oncoming traffic.
It’s certainly encouraged in the UK, for the reason Jayrot describes, that it would cause gridlock otherwise. The timing of the traffic lights makes it possible to complete the turn safely. A friend of mine was chastised by a driving examiner for ‘impeding the flow of traffic’ when she didn’t pull out in such a situation (although she did still pass the test).
Two cars seems to be the standard amount of cars that can turn left on a green light many places here in Los Angeles. These are intersections where the traffic doesn’t let up so the only way to turn is on the yellow/red after the green is finished. I’ve often seen three cars make it, with the third clearly running a red light in order to avoid waiting some more. And I’ve probably seen a fourth car a few times but I don’t recall right now. These situations are always made more exciting by idiots who blatantly run the red light in the opposite direction, creating a sort of “chicken” game between the hopeful left-turner(s) and the oncoming moron(s). Will he stop? Will he run the red light? Will I sit here in the intersection all day?
When I lived in Henderson, Nevada, I got a ticket for being past the line and not making the left before the light turned red. [slight hijack]What really sucked was that the cop who gave me the ticket was the reason I couldn’t make the turn. He was gcoming towards me and I would have had time to go, but he turned on his lights and speeded up. I didn’t want to cross into the path of a speeding cop, so I didn’t go. Right before he got to the intersection, he turned off his lights and the light turned red. I had no choice but to turn on the red, as I was in the intersection. He told me that you shouldn’t cross the line unless you’re sure you can make the turn. [/end sh]
Peace - DESK