I'm looking to find or make a list of how left turn phasing is done by all of the state DOTs for use in an ongoing argument. From what I've seen (and with state names in bold reflecting comments):
* Colorado: Generally leading, but willing to use lagging
* Illinois: Varies by district
- Chicago District - 99.5% lead only
- District that has Bloomington-Normal - does lead-lag on BL 55/Veterans Parkway, otherwise seems to be lead only
- Springfield District - 90% leading, though some lead-lag at intersections with dual left turn lanes
- Collinsville District - Lead only or split phasing
* Indiana: Seems to use leading and lead-lag
* Iowa: the DOT lets the cities handle the signals, but they seem to favor lead only
* Kentucky - Seems to use leading, lead-lag, and Dallas phasing with some of the flashing yellow arrow signals
* Louisiana: Generally leading
* Maryland: Leading
* Michigan: Lagging for permissive-protected, lead-lag for protected only
* Missouri - Uses a mix of lead, lead-lag, and Dallas phasing on intersections with flashing yellow arrows. There's also at least one intersection where the left turn arrow for one direction can come back up before the side street is given a chance to go.
* Nebraska: Lets the cities handle the signals, but they seem to stick with lead only
* New Jersey: Leading
* New York: Lead-lag, but with newer signals being lead only
* Ohio: Leading
* Oklahoma: No consistent/preferred method
* Wisconsin: Leading with the exception of a couple diamond interchanges
* Wyoming: At least in Cheyenne near I-180 some of the signals used lagging lefts.
Ohio:
Leading left most places. Sometimes, the side streets go one after the other, though. A few instances of lagging left, mostly at diamond interchanges I think.
Quote from: Revive 755 on September 09, 2012, 11:33:19 PM
I'm looking to find or make a list of how left turn phasing is done by all of the state DOTs for use in an ongoing argument. From what I've seen:
* Illinois: Varies by district
- Chicago District - 99.5% lead only
- District that has Bloomington-Normal - does lead-lag on BL 55/Veterans Parkway, otherwise seems to be lead only
- Springfield District - 90% leading, though some lead-lag at intersections with dual left turn lanes
- Collinsville District - Lead only or split phasing
* Indiana - Seems to use leading and lead-lag
* Iowa - the DOT lets the cities handle the signals, but they seem to favor lead only
* Missouri - Uses a mix of lead, lead-lag, and Dallas phasing on intersections with flashing yellow arrows. There's also at least one intersection where the left turn arrow for one direction can come back up before the side street is given a chance to go.
* Nebraska - Lets the cities handle the signals, but they seem to stick with lead only
* Wyoming - At least in Cheyenne near I-180 some of the signals used lagging lefts.
On the very few Chicago intersections that actually have arrows...
Upstate New York is almost entirely doghouse or all-permissive; whether it's leading or lagging seems to be random. Newer divided highways often have fully protected leading lefts.
Michigan: The flashing red ball for the permissive lefts in the state leads to the use of lagging lefts (probably the same for Delaware). Even with the new flashing yellow arrow installs MDOT uses lagging lefts almost exclusively.
EDIT: The near exclusive use of lagging lefts is used at permissive left turns. For protected lefts you may find more of a mix of leading/lagging operation.
I've seen Wisconsin lefts showing up in Austin TX (separated left turn lane, separated by an island from the main flow of traffic)
As far as I know Maryland is pretty much dual lead, with roads like US 40 getting protected lefts and roads like MD 26 getting protected/permissive. For the side streets that are important, they usually get dual lead lag .
Colorado tends to default to leading protected left turn phasing. In my area, as I posted in a previous thread (https://www.aaroads.com/forum/index.php?topic=5952.0), CDOT changes the protected left turn phasing at intersections along U.S. 50 by time of day for traffic flow.
Quote from: kphoger on September 10, 2012, 11:21:35 AM
Quote from: Revive 755 on September 09, 2012, 11:33:19 PM
I'm looking to find or make a list of how left turn phasing is done by all of the state DOTs for use in an ongoing argument. From what I've seen:
* Illinois: Varies by district
- Chicago District - 99.5% lead only
- District that has Bloomington-Normal - does lead-lag on BL 55/Veterans Parkway, otherwise seems to be lead only
- Springfield District - 90% leading, though some lead-lag at intersections with dual left turn lanes
- Collinsville District - Lead only or split phasing
* Indiana - Seems to use leading and lead-lag
* Iowa - the DOT lets the cities handle the signals, but they seem to favor lead only
* Missouri - Uses a mix of lead, lead-lag, and Dallas phasing on intersections with flashing yellow arrows. There's also at least one intersection where the left turn arrow for one direction can come back up before the side street is given a chance to go.
* Nebraska - Lets the cities handle the signals, but they seem to stick with lead only
* Wyoming - At least in Cheyenne near I-180 some of the signals used lagging lefts.
On the very few Chicago intersections that actually have arrows...
Chicago is a special case within Illinois, as CDOT (Chicago Department of transportation) installs and maintains the signs and signals, not IDOT within the city. Hence the differing signal, signage, and lighting types. IDOT only maintains the freeways (except Lake Shore Drive) within the city.
* Oklahoma - if you're asking for a consistent method of doing something Oklahoma follows, you must have never been to Oklahoma.
Louisiana - Mostly leading that I've seen, though some rare intersections use a lagging left instead of or in addition to a leading left.
New Jersey - almost exclusively leading, although there are a few lagging (Cross Keys Rd & Atlantic City Expressway Exit 41 ramps in Gloucester, NJ have two of the rare lagging left turn phases).
Quote from: vtk on September 09, 2012, 11:48:34 PM
Ohio:
Leading left most places. Sometimes, the side streets go one after the other, though. A few instances of lagging left, mostly at diamond interchanges I think.
There are quite a few lead-lag on surface streets around Columbus. Some might be maintained by the city, though.
Quote from: jeffandnicole on September 11, 2012, 10:04:39 AM
New Jersey - almost exclusively leading, although there are a few lagging (Cross Keys Rd & Atlantic City Expressway Exit 41 ramps in Gloucester, NJ have two of the rare lagging left turn phases).
It's possible that all lagging lefts are on non-NJDOT roadways. The other ones I know of are on county roadways. NJDOT uses lead phasing or split phasing, at least as far as I've done signal timing work with them. We've never really tried to push them on that...
Quote from: deanej on September 10, 2012, 11:28:34 AM
Upstate New York is almost entirely doghouse or all-permissive; whether it's leading or lagging seems to be random. Newer divided highways often have fully protected leading lefts.
I have seen a couple of intersections in Buffalo with lagging lefts for both protected left turns (case in point, Transit Road near Ted's Hot Dogs in Williamsville). The rest appear to be leading.
Quote from: 6a on September 11, 2012, 10:57:16 AM
Quote from: vtk on September 09, 2012, 11:48:34 PM
Ohio:
Leading left most places. Sometimes, the side streets go one after the other, though. A few instances of lagging left, mostly at diamond interchanges I think.
There are quite a few lead-lag on surface streets around Columbus. Some might be maintained by the city, though.
Toledo is quite ardent in lead-lag setups. These are easy to distinguish because all leads are protected-only while lags are permissive-protected.
Quote from: Steve on September 11, 2012, 08:50:32 PM
Quote from: jeffandnicole on September 11, 2012, 10:04:39 AM
New Jersey - almost exclusively leading, although there are a few lagging (Cross Keys Rd & Atlantic City Expressway Exit 41 ramps in Gloucester, NJ have two of the rare lagging left turn phases).
It's possible that all lagging lefts are on non-NJDOT roadways. The other ones I know of are on county roadways. NJDOT uses lead phasing or split phasing, at least as far as I've done signal timing work with them. We've never really tried to push them on that...
Found one...although it's actually a combo lead-lag!
Cass Street at NJ 29 (at the Trenton Thunder Stadium). NJ 29 has a 150' or so median between the NB & SB lanes. Traffic intending to turn left off NJ 29 turning into this short portion of Cass St, and waits at the traffic light. When NJ 29 gets the red, the inner part of Cass Street gets the lead green arrow for traffic to turn left or go straight across NJ 29. After a few seconds, NJ 29 has a full green. After traffic has cleared the outer portion, the light turns red preventing traffic from entering the inner portion. The inner portion then gets the lagging green to clear out the inner portion of Rt. 29.
Follow that?
Quote from: jeffandnicole on September 12, 2012, 04:05:35 PM
Quote from: Steve on September 11, 2012, 08:50:32 PM
Quote from: jeffandnicole on September 11, 2012, 10:04:39 AM
New Jersey - almost exclusively leading, although there are a few lagging (Cross Keys Rd & Atlantic City Expressway Exit 41 ramps in Gloucester, NJ have two of the rare lagging left turn phases).
It's possible that all lagging lefts are on non-NJDOT roadways. The other ones I know of are on county roadways. NJDOT uses lead phasing or split phasing, at least as far as I've done signal timing work with them. We've never really tried to push them on that...
Found one...although it's actually a combo lead-lag!
Cass Street at NJ 29 (at the Trenton Thunder Stadium). NJ 29 has a 150' or so median between the NB & SB lanes. Traffic intending to turn left off NJ 29 turning into this short portion of Cass St, and waits at the traffic light. When NJ 29 gets the red, the inner part of Cass Street gets the lead green arrow for traffic to turn left or go straight across NJ 29. After a few seconds, NJ 29 has a full green. After traffic has cleared the outer portion, the light turns red preventing traffic from entering the inner portion. The inner portion then gets the lagging green to clear out the inner portion of Rt. 29.
Follow that?
Only follow that because I was just at a game. But that's a clearance interval within an extended intersection more than a lagging left situation. There's no "lagging left trap" because 29 is one-way on each side.
* Nevada: The default tends to be dual leading lefts. However, any jurisdiction employing any reasonable amount of regional signal timing coordination (i.e. the Las Vegas Valley, Reno/Sparks, and maybe Carson City) will use a combination of lead-lead, lead-lag and lag-lag phasing. In fact, many areas of the Vegas valley and some areas of Reno/Sparks will vary left turn style at a single intersection by time of day.
In coordinated systems, lead-lag is highly preferred as it helps increase progression bandwidth for traffic flowing in one direction.
QuoteIn coordinated systems, lead-lag is highly preferred as it helps increase progression bandwidth for traffic flowing in one direction.
Some authors from the University of Nevada, Reno wrote a paper titled "Effectiveness of Lead—Lag Phasing on Progression Bandwidth". The study was based on a computer program maximizing the progression bandwidth from a number of signal system scenarios. More than 70% of the time the computer program picked a lead-lag phasing to maximize the progression green band. However, the study also stated:
QuoteThe number of signals had a profound impact on bandwidth attainability, exhibiting a nonlinear decline in attainability and bandwidth with an increasing number of signals in a system.
The problem Vegas has is it's a city with 1/2 mile by 1/2 mile blocks leading to closely spaced intersections that stop both directions of travel. As the number of signals that stop both directions of travel goes up, the potential for good dual progression decreases dramatically. Detroit is the only major metro in the US that has the ability to provide long stretches (10+ miles) of good dual progression along major arterials (thanks to the widespread use of Michigan Lefts and Superstreet designs).
Arizona: Leading, with Tucson often doing its own thing (http://cms3.tucsonaz.gov/transportation/left-turn-arrows (http://cms3.tucsonaz.gov/transportation/left-turn-arrows) and www.radixeng.com/reports/LeadLagExecSummary.pdf (http://www.radixeng.com/reports/LeadLagExecSummary.pdf))
California: Leading. Almost exclusively, to the point where it drives me insane to watch other drivers creep forward when I know their green isn't next.
Quote from: tradephoric on September 13, 2012, 05:09:13 PM
QuoteIn coordinated systems, lead-lag is highly preferred as it helps increase progression bandwidth for traffic flowing in one direction.
Some authors from the University of Nevada, Reno wrote a paper titled "Effectiveness of Lead—Lag Phasing on Progression Bandwidth". The study was based on a computer program maximizing the progression bandwidth from a number of signal system scenarios. More than 70% of the time the computer program picked a lead-lag phasing to maximize the progression green band. However, the study also stated:
QuoteThe number of signals had a profound impact on bandwidth attainability, exhibiting a nonlinear decline in attainability and bandwidth with an increasing number of signals in a system.
The problem Vegas has is it's a city with 1/2 mile by 1/2 mile blocks leading to closely spaced intersections that stop both directions of travel. As the number of signals that stop both directions of travel goes up, the potential for good dual progression decreases dramatically. Detroit is the only major metro in the US that has the ability to provide long stretches (10+ miles) of good dual progression along major arterials (thanks to the widespread use of Michigan Lefts and Superstreet designs).
I have taken traffic engineering classes from or with the authors of that paper...I might have even edited that paper back when I was a grad student in civil engineering.
The spacing of major signals in Vegas on the 1/2-mile grid actually isn't too bad for dual progression they have going. There are times when you can go 5-6 miles without stopping on some arterials if you're driving the speed limit--the longer cycle lengths do help this in some regard.
Quote from: mp_quadrillion on September 13, 2012, 05:30:38 PM
California: Leading. Almost exclusively, to the point where it drives me insane to watch other drivers creep forward when I know their green isn't next.
That annoys me even when the green is next. Maybe it's just because I drive a stick, but it always makes me think "silly automatics, the light is still red".
California has some lag lefts, as well as some that are both lead and lag.
Mira Mesa Blvd at Scranton in San Diego still baffles me.
http://goo.gl/maps/ob1pa
sometimes I think it is non-cyclic, because I've seen both lead and lag and can never predict which one is going to come up. It is synchronized to the 805 offramp at Mira Mesa, and also Scranton at Morehouse, and the next few lights to the east on Mira Mesa, and probably the 805 offramp at Sorrento Valley as well.
it's probably as well-timed as is possible, without redesigning that entire clusterfuck of an interchange complex. a lot of the time, traffic coming off 805 north can get a set of greens to guide them to Mira Mesa, Scranton, and Morehouse. Qualcomm's buildings are all on Morehouse, which implies a lot of traffic making that particular set of turns.
Quote from: tradephoric on September 13, 2012, 05:09:13 PMDetroit is the only major metro in the US that has the ability to provide long stretches (10+ miles) of good dual progression along major arterials (thanks to the widespread use of Michigan Lefts and Superstreet designs).
and the absence of vehicular traffic.
Quote from: agentsteel53 on September 14, 2012, 11:39:01 AM
Quote from: tradephoric on September 13, 2012, 05:09:13 PMDetroit is the only major metro in the US that has the ability to provide long stretches (10+ miles) of good dual progression along major arterials (thanks to the widespread use of Michigan Lefts and Superstreet designs).
and the absence of vehicular traffic.
He said
metro. Although I do find it a rather dubious claim it could be the
only metro capable of good dual progression. I would have to think a similar rate of progression could be achieved with jughandles or any other mechanism that minimizes left-turn phases.
Quote from: mp_quadrillion on September 13, 2012, 05:30:38 PM
California: Leading. Almost exclusively, to the point where it drives me insane to watch other drivers creep forward when I know their green isn't next.
While leading is more prevalent than any other phasing, I don't think "exclusively" is the correct term. There are a number of signals in the San Jose area that are lead-lag (Prospect Rd and Lawrence Expwy, Stevens Creek Blvd and Bubb Rd, De Anza Blvd and Homestead Rd, De Anza Blvd and Stevens Creek Blvd.. just to name a few). What's interesting is the left-turn phasing varies by time of day. For example, the Prospect left turns onto Lawrence are eastbound lead-westbound lag in the morning, lead both ways during the mid-day and at night, westbound lead-eastbound lag in the evening. The left turn signals from Stevens Creek Blvd to Bubb Rd are lead-lag during the day but are lead-only at night. The signal from Stevens Creek onto northbound CA-85 is always a lag.
Quote from: agentsteel53 on September 14, 2012, 11:39:01 AM
Quote from: tradephoric on September 13, 2012, 05:09:13 PMDetroit is the only major metro in the US that has the ability to provide long stretches (10+ miles) of good dual progression along major arterials (thanks to the widespread use of Michigan Lefts and Superstreet designs).
and the absence of vehicular traffic.
According to MDOT, Telegraph Road has an ADT of 72,300 between I-696 & 13 Mile Road which is one of the highest ADT's of any major arterial in America (see the Busiest Local Arterial Street by ADT post in this forum). Telegraph provides good 2-way progression where it is possible to drive 10 miles in each direction without getting stopped at a red light.
There are days when NB Telegraph is a parking lot during the PM rush as people working in Detroit are going north to get home. However, since Telegraph is timed for good 2-way progression the light SB traffic can enjoy good progression even when NB traffic is bumper to bumper. The worst case scenario is traffic engineers time the traffic signals along a corridor to achieve good progression for the heavy direction of travel at the expense of green-to-red progression for the light direction of travel....but the heavy direction of travel is a parking lot and nobody is happy.
Quote from: roadfro on September 14, 2012, 05:45:39 AM
The spacing of major signals in Vegas on the 1/2-mile grid actually isn't too bad for dual progression they have going. There are times when you can go 5-6 miles without stopping on some arterials if you're driving the speed limit--the longer cycle lengths do help this in some regard.
The 1/2 mile grid with traffic signals stopping both directions of travel every 2,640 feet isn't conducive to achieving good dual progression. The signals would have to run an 80 second cycle to achieve good dual progression but there are a number of reasons why an 80 second cycle isn't practical:
- The time it takes vehicles to start moving at the beginning of the phase and the required safety minimums (yellow; all red time) soaks up too much of the phase time.
- The required pedestrian intervals in the MUTCD often forces the signal to run long cycle lengths.
Time-distance diagram (80 second cycle)(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2Ftimedistance80.jpg&hash=c033ad425fa3b097af4e71b934d0f6325f04ffe5)
Anything over an 80 second cycle leads to bad progression in at least one-direction of travel. Maximizing the progression band in one-direction leads to a mind field of red lights in the opposite direction. The time-distance diagram below is for a corridor with simple 2-phased signals and achieving good dual progression becomes even more difficult when left-turn phases are present (regardless if a lead-lag setup is being used). I don't doubt you can drive 5-6 miles in one direction but achieving good dual progression is questionable.
Time-distance diagram (120 second cycle)(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2Ftimedistance120.jpg&hash=349ea50cedc3cbe08c17f7edcc01ce1df4e0b5d0)
Quote from: Revive 755 on September 09, 2012, 11:33:19 PM
...
* Wisconsin: Leading with the exception of a couple diamond interchanges
Most of the updated (new, reconstructed, or re-timed) interchanges are favoring lead-lag phasing. Signals operated by local municipalities are almost exclusively lead, unless the signal is left in fully-actuated mode.
Minnesota: used to be lead only; they started introducing lags about 15 years ago. Now we have lead/lags too, but lead is still by far the most common. MN also has a *lot* (nanny state complex? conservative engineers?) more protected only turns, even though permissive/protected is becoming more common.
Quote from: myosh_tino on September 14, 2012, 03:23:54 PM
Quote from: mp_quadrillion on September 13, 2012, 05:30:38 PM
California: Leading. Almost exclusively, to the point where it drives me insane to watch other drivers creep forward when I know their green isn't next.
While leading is more prevalent than any other phasing, I don't think "exclusively" is the correct term. There are a number of signals in the San Jose area that are lead-lag (Prospect Rd and Lawrence Expwy, Stevens Creek Blvd and Bubb Rd, De Anza Blvd and Homestead Rd, De Anza Blvd and Stevens Creek Blvd.. just to name a few). What's interesting is the left-turn phasing varies by time of day. For example, the Prospect left turns onto Lawrence are eastbound lead-westbound lag in the morning, lead both ways during the mid-day and at night, westbound lead-eastbound lag in the evening. The left turn signals from Stevens Creek Blvd to Bubb Rd are lead-lag during the day but are lead-only at night. The signal from Stevens Creek onto northbound CA-85 is always a lag.
You're right, of course. "Prevalent", "preferred" or "default" would have been better terms.
And as you pointed out, the phasing can vary based on lopsided traffic volumes or the need to keep a certain segment moving (or prevent a huge platoon from entering an already-saturated freeway). The older streets, especially, can use a split phasing; whereas newer arterials will tend toward leading during non-peak hours.