A standard traffic signal has two phases, one for N-S traffic and one for E-W traffic.
When one direction inocorporates a left turn signal, you now have three phases, N-S, E-W, and turning off the N-S. To the extent that the left turn signal is one direction or two directions (i.e. from NB to WB and from SB to EB), you still have only three phases, whether its lead-lead or lag-lag, even if the time or each left turn is not the same and otherwise incoporates part of the through phase. (Its arguable whether a lead-lag setup adds one additional phase or two to the main intersection, perhaps that can be discussed further in the replies.)
When both directions have left turn signas, you have four phases: N-S, E-W, lefts from the N-S street, lefts from the E-W street.
A diagonal street crossing though the intersection would add in an additional phase.
An all-ped phase (with or without diagonal crossing) would add in an additional phase. [But I would not include a 5 second lead pedestrian interval or "ped head start" as a separate phase.]
With all that out of the way, are there any signals out there with a large number of signal phases, (i.e. more than 4)?
There is some practical consideration here as I was trying to get the county here to install a left turn signal from E-W to N-S street at an intersection that already has four phases (lefts off of N-S street, N-S, E-W, all-ped). The county told me that they cannot take time away from the other phases to install a fifth phase (for lefts off of E-W street) without causing backups for the N-S street, which is the heaviest traffic load. [The all-ped phase is rare in this county, but needed at this intersection because of unique pedestrian safety issues.] Basically, in the county's view, they cannot install a fifth phase and would only install a left signal if they got rid of the all-ped phase which is needed here.
So if there are 5 or more phased signals out there, please discuss.
This light in Ogden, Utah (https://www.google.com/maps/@41.2592614,-111.9696913,139m/data=!3m1!1e3) appears to be 5 phases, if I'm understanding this correctly:
-one for N/S thru traffic
-one for E/W thru traffic
-one for traffic coming in from the NW
-one for the N/S protected lefts
-one for the E-to-N left turn
This signal in Tacoma, WA (https://www.google.com/maps/@47.2560458,-122.4627064,238m/data=!3m1!1e3) with five phases is probably the most in Pierce County.
Five-way intersection:
1) northbound Sprague
2) southbound Sprague
3) westbound 6th Ave
4) Left turns from 6th/Division (through road turns into Division)
5) Straight/right turns from 6th/Division
Ultimately, it could be simplified by eliminating the protected left turns from 6th/Division (phase 4), and removing the split-phasing from Sprague (combining phases 1+2).
Problem is that the intersection, as it stands, is probably one of the oldest in the city: 8-inch signals for everything except the arrows, hanging plywood lane-use arrows for assigning the signals themselves (not something I've seen outside Tacoma), and incandescent bulbs (pretty rare around here at this point).
I believe the signal is actuated, but the controllers seem to be ancient. I've seen "green for ghosts" (green for no one) many times at this intersection, with the left turns sometimes lasting much longer than necessary; sometimes, the left turns for 6th/Division will activate, followed immediately by another random phase, and then the through traffic gets to go. The whole intersection desperately needs work.
How about US 30 at Caton Farm Road and Gaylord Road in Joliet, IL? (https://goo.gl/maps/Nxr6yjgomafoVMf96). Could be 12 phases here.
Might be the same for US 30 at Raymond Street and Black Road in Joliet, IL. (https://goo.gl/maps/ymVKz5EWRn7P38CN7)
Anyone remember how many phases MO 367 had for the intersections between I-270 and US 67 prior to the freeway upgrades? I recall those being long with separate phases for the frontage roads.
The definition of "phase" is a bit muddied here–understandably as there's an old-school perception of "phase" versus the technical definition of "phase".
The way "phase" is defined in controller operations is that each signalized movement/right-of-way assignment is a separate phase. So in a typical four-legged intersection with protected left turn control, there's actually eight phases (one phase for each through direction, and another phase for each left turn direction). It may so happen that some of these begin and terminate together (for example, a NB left turn and SB left turn), but they're technically separate phases. The controller can assign those phases in different orders and different lengths based on how the engineer sets the timing. Things start getting more complicated when you introduce other concepts, such as right turn overlap phases.
The five-legged intersection US 89 linked to looks like it has 9 phases–the eight phases of a standard four way intersection, plus an extra phase for the traffic coming from the northwest (I assume that direction's left turn and through movements happen together with no conflicts).
The six-legged intersections Revive 755 linked to would indeed have 12 phases, as it appears each leg has both a through and protected left turn phase.
The five-legged intersection Jakeroot discussed (link (https://www.google.com/maps/@47.2559459,-122.4627905,203m/data=!3m1!1e3)) appears to have 7 phases based on his description of the operation, as the left turn and straights from EB 6th/WB Division are two phases each.
Quote from: Revive 755 on February 16, 2020, 11:44:36 PM
How about US 30 at Caton Farm Road and Gaylord Road in Joliet, IL? (https://goo.gl/maps/Nxr6yjgomafoVMf96). Could be 12 phases here.
Might be the same for US 30 at Raymond Street and Black Road in Joliet, IL. (https://goo.gl/maps/ymVKz5EWRn7P38CN7)
Anyone remember how many phases MO 367 had for the intersections between I-270 and US 67 prior to the freeway upgrades? I recall those being long with separate phases for the frontage roads.
Raynor Avenue, not Raymond Street, and the other streets are Plainfield Road (US-30), Black Road (west of the intersection), and Ruby Street (east of the intersection).
There are 12 phases there at Six Corners as each leg has a protected left, and are as follows:
- Raynor left turns
- Raynor through and right turns
- Plainfield (US-30) left turns
- Plainfield through and right turns
- Black/Ruby left turns
- Black/Ruby through and right turns
Quote from: roadfro on February 17, 2020, 04:14:37 PM
The five-legged intersection Jakeroot discussed (link (https://www.google.com/maps/@47.2559459,-122.4627905,203m/data=!3m1!1e3)) appears to have 7 phases based on his description of the operation, as the left turn and straights from EB 6th/WB Division are two phases each.
Thank you for reminding me that I forgot to include a link to the location! Bit unlike me to forget that.
Quote from: mrsman on February 16, 2020, 11:27:58 AM
A standard traffic signal has two phases, one for N-S traffic and one for E-W traffic.
When one direction inocorporates a left turn signal, you now have three phases, N-S, E-W, and turning off the N-S. To the extent that the left turn signal is one direction or two directions (i.e. from NB to WB and from SB to EB), you still have only three phases, whether its lead-lead or lag-lag, even if the time or each left turn is not the same and otherwise incoporates part of the through phase. (Its arguable whether a lead-lag setup adds one additional phase or two to the main intersection, perhaps that can be discussed further in the replies.)
When both directions have left turn signas, you have four phases: N-S, E-W, lefts from the N-S street, lefts from the E-W street.
A diagonal street crossing though the intersection would add in an additional phase.
An all-ped phase (with or without diagonal crossing) would add in an additional phase. [But I would not include a 5 second lead pedestrian interval or "ped head start" as a separate phase.]
With all that out of the way, are there any signals out there with a large number of signal phases, (i.e. more than 4)?
There is some practical consideration here as I was trying to get the county here to install a left turn signal from E-W to N-S street at an intersection that already has four phases (lefts off of N-S street, N-S, E-W, all-ped). The county told me that they cannot take time away from the other phases to install a fifth phase (for lefts off of E-W street) without causing backups for the N-S street, which is the heaviest traffic load. [The all-ped phase is rare in this county, but needed at this intersection because of unique pedestrian safety issues.] Basically, in the county's view, they cannot install a fifth phase and would only install a left signal if they got rid of the all-ped phase which is needed here.
So if there are 5 or more phased signals out there, please discuss.
The seem to change it every time I'm there, but I think that there are numerous phases on many of the signals involving Las Vegas Blvd. This would particularly be the case when two or three entrances into casino properties don't exactly line up.