Left turn phasing by state

[rawmustard]

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.

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.

[myosh_tino]

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.

[tradephoric]

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.

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.

[tradephoric]

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)


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)

[DaBigE]

...
* 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.

[Mdcastle]

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.

[mp_quadrillion]

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.