Traffic Light Phases

[froggie]

Regarding the phasing mapman posted, we have an intersection in Alexandria (US 1 at the north end of Potomac Yard) that has something similar.  There are two left turn phases for southbound US 1 traffic making the left turn into Potomac Yard...both lead and lag.  Northbound US 1 traffic turning into the Toyota dealership just gets a lead left.  Unlike the Arizona example, this is an all-day event.

Curiously, the southbound approach has the room for a dual-left-turn lane here, but is only striped for a single lane...mainly because the side road into Potomac Yard only has room for a single lane.

[Michael]

Thanks for this thread; I understand lead and lag turns now!

In Central NY, I usually see lead-lead, or left/thru while the other direction is all red.  I don't recall ever seeing any other setup in my travels in the rest of NY, PA, and MD.

One stoplight in Auburn (map) has lead/lead for NY 5 traffic turning onto McIntosh Drive and into McDonalds, and a right-turn arrow for McIntosh Drive to NY 5 at the same time.  Oddly, there are no "No Turn On Red" signs, but the next light west at NY 5/Standart Ave/North Seward Ave (map) has them.  That light has the same setup, except for the right-turn arrow.

There's another light east of McDonalds at NY 5/Brookside Drive/John Walsh Blvd. (map) that has the weirdest phases ever.  Traffic on the side streets sometimes gets a green in one direction only, so there are red balls in three directions.  I saw the same thing happen at NY 34/38/Elizabeth St./Chedell Pl. (map).  I'm guessing it's to allow people to turn left on to the main road whithout using a dedicated left-turn phase.

P.S.: The stoplight at NY 5/Brookside Drive/John Walsh Blvd. has crossing lights for the sidewalks along NY 5 that terminate, and then turn back to white while there is a green ball for NY 5.  I counted it four times one night.  Even weirder is that sometimes one side of NY 5 has a white person, and the other side has an orange hand at the same time.

[froggie]

Since you mention central NY, I want to say I remember some of the signals in Liverpool and Clay having a lag left instead of a lead left.  Henry Clay Blvd and Taft Rd seems to come to mind.  But I haven't been up there in 5 years.

[Michael]

I was walking near the stoplight at NY 5/McIntosh Drive/McDonalds I mentioned above (map) earlier this evening, and saw the left turn arrow to McIntosh Drive come on during the middle of the thru phase for NY 5 traffic (opposing NY 5 traffic had a red ball).  As far as I can recall, this is the first time I have ever seen yellow trap.

[Ace10]

Hey fellow roadgeeks, got a question for ya:

I'm not sure if this is commonplace or not, but it is one of the first times I've ever seen this happen. Just south of Winter Garden, FL, they are working on reconstructing part of CR-535 (Winter Garden Vineland Rd). Lots of this construction is occurring near where NB CR-535 makes a 90-degree right turn from the west to continue going north. This is at the intersection of CR-535 and Fiquette-Hancock Rd and Summerport Village Pkwy.

Anyway, previously there used to be a circular green signal from NB CR-535 traffic facing west, with an additional left-turn arrow. Not sure about the other sides of the intersection. But now, the same west-facing traffic now sees a circular green with green left-turn arrow, and an additional TWO right-turn arrows.

When the western-facing traffic has a red light, the right-turn arrows are green up to a certain point (as one would expect). But when the western-facing traffic gets a green, the right-turn arrows are red. I can see a couple of reasons for this: these arrows cannot be green if pedestrians have to have time to legally cross the intersection on the north side, and the arrows also cannot be green if the opposite side has a left-turn permissive signal (which I'm not sure if it does at this point, or will once the intersection is done). But to have the arrows red, requiring a stop but allowing traffic to proceed to turn right after a stop (legal in FL), seems like a major inconvenience. There is a lot of right-turning traffic at this intersection, so having all vehicles stop at a red right-turn arrow when their side has a green signal seems like a bad choice. The right-turn signal should have permissive right-turn circular greens while having the arrows extinguished - though I'm not sure if this is MUTCD-compliant with two turning lanes.

Has anyone seen anything like this before?

[hobsini2]

There are a couple of intersections in Chicago, namely Cicero and Archer, that are using the protected arrow after the yellow ball light.

[Amtrakprod]

In pretty much every city I have ever lived, traffic lights seem to flow in the following order at a standard intersection of two roughly equally important arterials where left turns are allowed with a green ball but there is an arrow

Arterial #1 Left Turns
Arterial #1 All traffic
Arterial #2 Left Turns
Arterial #2 All traffic

I just moved down to Tucson, however, and noticed that things are a bit different- the general flow is

Arterial #1 All traffic
Arterial #1 Left Turns
Arterial #2 All traffic
Arterial #2 Left Turns

The main advantage to this that I noticed is that if you're sitting in the middle of an intersection waiting for a left turn with a green ball and the light turns yellow, the next phase is going to be a protected left anyway so you're not sort of running the red light by hanging out in the intersection, and then once the protected phase is done traffic from the other direction gets to move.

I have never seen this before- do any other cities employ that sort of phasing?

Here's a video about the change: https://youtu.be/CSzSDWCmE7Y


iPhone

[US 89]

Only in Arizona will the temperature be 89 degrees on the 6:30 AM news. 

From what I've observed, Utah is largely a leading-left state, though I can think of several lead-lag signals. I think there might be some lagging lefts in Utah County, but those are by far the least common, and I notice it whenever I drive through one. This goes for both fully protected and permissive (FYA or doghouse) signals, though lead-lag phasing is significantly more common on FYAs.

[ipeters61]

Delaware has a handful of these as far as I know, to an extent.

DE-72 at US-40 (Bear)
1. DE-72 Through
2. DE-72 Left Turns
3. US-40 Left Turns
4. US-40 Through

DE-896/US-301 at Glasgow Avenue/Porter Road (Glasgow)
1. Glasgow/Porter Through
2. Glasgow/Porter Left Turns
3. DE-896/US-301 Left Turns
4. DE-896/US-301 Through

[mrsman]

In pretty much every city I have ever lived, traffic lights seem to flow in the following order at a standard intersection of two roughly equally important arterials where left turns are allowed with a green ball but there is an arrow

Arterial #1 Left Turns
Arterial #1 All traffic
Arterial #2 Left Turns
Arterial #2 All traffic

I just moved down to Tucson, however, and noticed that things are a bit different- the general flow is

Arterial #1 All traffic
Arterial #1 Left Turns
Arterial #2 All traffic
Arterial #2 Left Turns

The main advantage to this that I noticed is that if you're sitting in the middle of an intersection waiting for a left turn with a green ball and the light turns yellow, the next phase is going to be a protected left anyway so you're not sort of running the red light by hanging out in the intersection, and then once the protected phase is done traffic from the other direction gets to move.

I have never seen this before- do any other cities employ that sort of phasing?

Here's a video about the change: https://youtu.be/CSzSDWCmE7Y


iPhone

Leading lefts are by far more common than lagging lefts.  I believe this is because of yellow trap concerns that aren't present in leading lefts.  However, in most case where lefts are permitted-protected, if you give a leading left you will still have cars that will make the permitted turn at the end of the cycle, in effect giving cars a protected leading left and a turn on the yellow (or all red phase) lagging left without protection.  It would be far more efficient generally to combine these two lefts, hence a lagging left that is designed to avoid yellow trap (by using FYA, restricting one of the left turns, simultaneous lagging left doghouses, or other means) combines both movements and puts all the lefts at the end of the cycle.  As an additional bonus, it makes it easier to establish a leading pedestrian interval at the intersection.  Furthermore, to the extent that all the cars in the left turn lane can make a permitted turn during green orb, the green arrow doesn't necessarily have to come on.