Any traffic engineers here?

[Zeke]

What is the advantage to a left turn lane going green with the straight traffic and having the opposing left turn lane go green at the latter portion of the green light? It's a staggered system and I never liked it.

[legion]

The main road in Bloomington (Veterans Parkway--coincidentally the busiest road south of the Chicago area in the state seeing 50,000 cars a day) is like that. Further, the lights are timed so that the busy side gets the green arrow last. (In the morning, most traffic is south-bound and the south-bound left turn lane gets the green arrow last--the opposite is true in the evening.) I can tell you the effect. The speed limit is 45 mph and the effective speed during rush hour is 25-35 mph--all because of the poor light timing.

I think it is a scheme to limit traffic flow...like speed bumps or round-abouts.

[Porsche-O-Phile]

Also, where's the data to show that those infernal lights at freeway onramps actually do anything other than make you stop, then accelerate from a stop burning more fuel and creating more unnecessary delays?

[john70t]

The traffic lights in my area are definitely timed for fast acceleration with 5-10mph over the speed limit. The result is a lot of impatience and pedestrian near-misses in a small college town.

Drivers can't seem to figure out why I don't keep stomping on the gas until reaching the next red light, or give granny plenty of room while she's crossing the street.

[p911dad]

I know several real, honest to God traffic engineers very well, and all I can say is they are even more peculiar than other engineers(from a Real Estate guy point of view), and they have a have accepted a mission from on high to control traffic and therefore save lives. They have a bible too, it's called the MUCTD(manual of uniform traffic devices), and to them it is gospel. If you have questions about that stuff, always refer back to this. Check out the 2003 FHWA edition, they all follow it. Chapter 4 covers traffic signals in excruciating detail.

[p911dad]

Oops. Correction on that acronym- it is MUTCD, 2003, (not muctd)

[island911]

Originally Posted by Porsche-O-Phile

Also, where's the data to show that those infernal lights at freeway onramps actually do anything other than make you stop, then accelerate from a stop burning more fuel and creating more unnecessary delays?

+1

[TerryBPP]

I do some like TIS work. The reason for the timing difference is a function of the turn lane length. The timing of lights for a left turn lane is based on the opposing traffic volume, the # of trips using the turnlane, and the class of road (local, aterial, etc.). If there are turnlane restrictions that will not allow lengthening then the lights can be staggered to allow for more trips to go thru the light due to the insufficient storage.

My guess is the light was installed after the turnlane was in place and there was not room (or money) for lengthening the turnlane.

[sjf911]

Would a traffic engineer own a Porsche and be on PPOT? I would expect the stereotypical trade-off of safety, fuel economy, and durability like Toyota.

[red-beard]

Short turn lane means that it can block the traffic flow when the left is red.

[nota]

hate the red left turn lights
these are the same numbnuts who can't get the lights in sync
and lets hang the idiots who invented traffic calming and those stupid little circles
but the slow death is for the speed bumps and other things like tables

I use back streets to avoid the jams but all of the above are poping up all over my routes

[juanbenae]

milt got a ticket... i work with traffic engineers and they are forever interjecting their wishes into a job... cost time and money often enough to piss one off.


T$

[Zeke]

Originally Posted by k911sc

milt got a ticket... i work with traffic engineers and they are forever interjecting their wishes into a job... cost time and money often enough to piss one off.


T$

milt did not get a ticket.

My question had nothing to do with timed lights from one intersection to the next, nor did it have anything to do with long vs. short left turn lanes.

One side goes with the green light for straight traffic, while the other side waits. Then, the other side's straight traffic goes green. The "other side's" left turners have to wait until near the end of the green light to proceed. It's staggered from N to S, or E to W, depending. That's the situation I'm asking about.

The reason I object is they way I negotiate my way through the city it to take the first available light, be it a left, or straight (or a right vs straight). Seldom am I going only straight; it usually takes couple of turns (or many) to get to any destination. What I am saying is I turn at any opportunity that will save me from sitting at a red light.

If I can't read how the damn intersection works, I might be sitting in a left turn lane when I could have gone straight and been on down the road. What really pisses me off is that some intersections seem to work differently at different times of the day. I get caught thinking I know which light is going to change first and I'm stuck at a red.

Ever arrived in a left turn lane that is vacant just a little too late to get a green light? Then, you have to sit through all the N/S traffic as well as the E/W traffic before you go. Damn, that's annoying. There's so much traffic in So Cal, most of the time you get out of a lane you're in once you've chosen.

I'm just trying to save a few minutes. And yes, I do look ahead as far as I can see the lights to try to read what's going to happen. And yes, I laugh my ass off at all the jackrabbits that can't see a few hundred feet, rush up to the intersection and slam on the brakes. Some times when I'm just lagging behind, timing the lights, I will drive at an even speed right up their ass as they are accelerating off the the next light. The closer I get to hitting them at an even speed, the better the game. Or better yet, cruising on by in the other lane as they come off the line, ready to burn another gallon.

Nothing but dim wits out there. The engineers aren't helping, or are they?

PS, our city was all timed in the 60's. It's largely a big grid of right angles, so it was reasonably plausible. Then, they added all this crap here and there and you can't go 2 consecutive green lights to frequently. All stop and go, stop and go. What a waste. They say they are going to synchronize all the lights once again. With computers, I this is doable with special light changes for emergency vehicles (all red).

Let's git 'er dun.

[71T Targa]

I remember well sitting at a light at the south end of main street one late night, probably 20 years ago. There was no traffic, and I watched my light turn green and then the lights down the street turning green in succession.

It was beautiful seeing how timed these lights were, how each would turn green moments before I arrived. I was thinking about the work involved, and how smart the guys who designed this must have been.

Then I thought; What if I had been going the other way???

[Zeke]

Originally Posted by phred68

Then I thought; What if I had been going the other way???

Unevenly place lights will not synchronize perfectly in both directions and heavy traffic one way or f the other might make the timing wrong for too many cars. But, it works in theory going both ways, especially for streets laid out on a even grid in both directions.

That's where software comes in. I know an "adjustment period" every so many light changes, and for the time of day (traffic load) would do the job keenly in keeping the lights in sync.