Left turn phasing by state

[Revive 755]

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.

[vtk]

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.

[kphoger]

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...

[vdeane]

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.

[tradephoric]

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.

[texaskdog]

I've seen Wisconsin lefts showing up in Austin TX (separated left turn lane, separated by an island from the main flow of traffic)

[kj3400]

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 .

[The High Plains Traveler]

Colorado tends to default to leading protected left turn phasing. In my area, as I posted in a previous thread, CDOT changes the protected left turn phasing at intersections along U.S. 50 by time of day for traffic flow.

[Brandon]

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.

[Scott5114]

* Oklahoma - if you're asking for a consistent method of doing something Oklahoma follows, you must have never been to Oklahoma.

[Darkchylde]

Louisiana - Mostly leading that I've seen, though some rare intersections use a lagging left instead of or in addition to a leading left.

[jeffandnicole]

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).

[6a]

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.

[Alps]

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...

[MASTERNC]

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.

[rawmustard]

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.

[jeffandnicole]

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?

[Alps]

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.

[roadfro]

* 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.

[tradephoric]

In 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:

The 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). 

[mp_quadrillion]

Arizona: Leading, with Tucson often doing its own thing (http://cms3.tucsonaz.gov/transportation/left-turn-arrows and 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.

[roadfro]

In 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:

The 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.

[vdeane]

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".

[agentsteel53]

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.

[agentsteel53]

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).

and the absence of vehicular traffic.