Split Phasing, is it more of a curse than a help?

[mrsman]

What would be the term for single-direction-at-a-time phasing:  starting with full-movement W (all other directions red), full-movement E (again, all other directions red), full-movement S (you know the drill), full-movement S (yada, yada).  Each direction has both ball and arrow tri-colors and channelized left lanes with about a 7 vehicle capacity E/W and 5 vehicles N/S.  By far, largest volume is E-W; most S turns E or continues S, while very little turning movement NB.  What would you call such an intersection type: quad-phase, single-serve, or some other term that I'm not familiar with? 

Intersection in question:  Curtner Ave. and Almaden Road (aka Old Almaden) in San Jose, CA.  I've sat up to 5 minutes waiting to pass through this intersection -- which operates this way 24/7!  I avoid it whenever possible, although it's quite close to my residence.

I'd say that these are double split-phasing. And they are terrible.

[CtrlAltDel]

What would be the term for single-direction-at-a-time phasing:  starting with full-movement W (all other directions red), full-movement E (again, all other directions red), full-movement S (you know the drill), full-movement S (yada, yada).  Each direction has both ball and arrow tri-colors and channelized left lanes with about a 7 vehicle capacity E/W and 5 vehicles N/S.  By far, largest volume is E-W; most S turns E or continues S, while very little turning movement NB.  What would you call such an intersection type: quad-phase, single-serve, or some other term that I'm not familiar with? 

Intersection in question:  Curtner Ave. and Almaden Road (aka Old Almaden) in San Jose, CA.  I've sat up to 5 minutes waiting to pass through this intersection -- which operates this way 24/7!  I avoid it whenever possible, although it's quite close to my residence.

There's another one at Storke Road and Hollister Avenue in Goleta, California.

[sparker]

Double split phasing!  Wow!  Now I know what to call it when I complain to San Jose Traffic Planning -- which will likely fall on deaf ears, as they seem committed to citywide "traffic calming" (obviously no connection to driver calming!).  Likely the notion is to keep the traffic on westbound Curtner coming in waves or bunches; the neighborhood just west of the signal in question is Willow Glen, one of the pricier (and more politically active) sections of town.  Well, guess what -- as Robert Burns averred, "the best laid plans...."; I live a half-block off Curtner about a mile to the west, and traffic is not only spread out by that point, but pissed off enough to be traveling well over the 35 mph limit to make up time (it's the only multilane through E-W corridor in that part of town).  And since San Jose is about 150 cops short of their normal number (many leave for higher-paying gigs in Santa Clara, Sunnyvale, and Cupertino), speed enforcement is at or near the bottom of their priority list.  But the planners at least, to their peers, look like they're doing something -- even if it's just creating bottlenecks!

[mrsman]

Double split phasing!  Wow!  Now I know what to call it when I complain to San Jose Traffic Planning -- which will likely fall on deaf ears, as they seem committed to citywide "traffic calming" (obviously no connection to driver calming!).  Likely the notion is to keep the traffic on westbound Curtner coming in waves or bunches; the neighborhood just west of the signal in question is Willow Glen, one of the pricier (and more politically active) sections of town.  Well, guess what -- as Robert Burns averred, "the best laid plans...."; I live a half-block off Curtner about a mile to the west, and traffic is not only spread out by that point, but pissed off enough to be traveling well over the 35 mph limit to make up time (it's the only multilane through E-W corridor in that part of town).  And since San Jose is about 150 cops short of their normal number (many leave for higher-paying gigs in Santa Clara, Sunnyvale, and Cupertino), speed enforcement is at or near the bottom of their priority list.  But the planners at least, to their peers, look like they're doing something -- even if it's just creating bottlenecks!

You know the area better than I do, but looking at GSV it seems that only Curtner is split-phased.  Almaden Rd appears to be single phased with protective-only left turn phasing.  That is much better than a true double split-phasing situation, but it is still terrible for Curtner traffic. The main problem seems to be the narrow bridge over the Guadalupe River that can't be easily widened - so there is no way to fit a left turn lane with 2 eastbound and 2 westbound lanes. 

La Rue / Hutchison in Davis, CA (on the UCD campus) used to also be double split-phased, when I lived in the area about 20 years ago.  It now appears to be split phased only on La Rue.  A similar set up to Curtner/Almaden Rd.  I've felt that given the traffic patterns there, La Rue would be much better with 2 left turn lanes and one thru lane (each direction) than having the option lane (left or straight in the middle lane) which necessitates split-phasing.

The Sacramento area has a lot of split-phasing.  Usually done where there is no room for a left turn lane, particularly where a bike lane is installed. But I do not recall any double split-phasing.

[Mr_Northside]

What would be the term for single-direction-at-a-time phasing:  starting with full-movement W (all other directions red), full-movement E (again, all other directions red), full-movement S (you know the drill), full-movement S (yada, yada).  Each direction has both ball and arrow tri-colors and channelized left lanes with about a 7 vehicle capacity E/W and 5 vehicles N/S.  By far, largest volume is E-W; most S turns E or continues S, while very little turning movement NB.  What would you call such an intersection type: quad-phase, single-serve, or some other term that I'm not familiar with? 

Intersection in question:  Curtner Ave. and Almaden Road (aka Old Almaden) in San Jose, CA.  I've sat up to 5 minutes waiting to pass through this intersection -- which operates this way 24/7!  I avoid it whenever possible, although it's quite close to my residence.

I'd say that these are double split-phasing. And they are terrible.

I don't know I've ever heard terminology for it, but I do occasionally use this intersection in Avalon, PA that is all-way split-phase:

(GSV): https://goo.gl/maps/UWBYRkgw3tw

[cl94]

Split phasing has its uses and certain regions of NYSDOT make use of partial split-phasing, where one direction has a leading left and the other lagging. What I don't get is split phasing where normal phasing would work, especially if the intersection is NTOR. Take the intersection of 6th Avenue and Federal St in Troy. Goes NB-SB-Federal LT-Federal. Semi-actuated to extend if cars are still coming, but timed so all phases cycle. There could easily be left and right turn lanes in each direction on 6th, as turn volume is high and there is the space for it. Given the signal timing in Troy, you're almost guaranteed to get stopped at this light and, as it's NTOR, you're stuck there. Straight traffic isn't enough to warrant 2 through lanes and, heading SB, the right lane becomes a turn lane with no warning immediately south of the intersection, so it's a common accident spot as people are forced to change lanes.

[kphoger]

What would be the term for single-direction-at-a-time phasing:  starting with full-movement W (all other directions red), full-movement E (again, all other directions red), full-movement S (you know the drill), full-movement S (yada, yada).  Each direction has both ball and arrow tri-colors and channelized left lanes with about a 7 vehicle capacity E/W and 5 vehicles N/S.  By far, largest volume is E-W; most S turns E or continues S, while very little turning movement NB.  What would you call such an intersection type: quad-phase, single-serve, or some other term that I'm not familiar with? 

Intersection in question:  Curtner Ave. and Almaden Road (aka Old Almaden) in San Jose, CA.  I've sat up to 5 minutes waiting to pass through this intersection -- which operates this way 24/7!  I avoid it whenever possible, although it's quite close to my residence.

I'd say that these are double split-phasing. And they are terrible.

I don't know I've ever heard terminology for it, but...

This is the type of timing that Wichita uses for basically the whole daylight hours for intersections where Kellogg's frontage roads meet surface arterials.  It makes sense here, because the whole intersection can function as one big intersection that happens to have a freeway-sized gap in the middle.

What annoys the heck out of me is an intersection like this one in Mexico–which, incidentally, I'll probably be driving through on Monday.  It's not a busy intersection, the north and south approaches are barely skewed at all, yet it operates on "double split" phasing all the time.  There are several others in town that do the same thing.

[sparker]

Looking at the current GSV for the Curtner/Almaden intersection that was referred to by mrsman shows the previous configuration (from prior to 10 weeks ago, when that section was repaved and restriped); while the Guadalupe bridge wasn't widened, an actual left-turn lane from E. Curtner to N. Almaden was carved out by narrowing the travel lanes to 10 feet.  A new massive condo complex about a half-mile north of Curtner on Almaden Rd. opened its latest phase a couple of months ago (this has been the subject of a running political/planning local controversy at least since I moved to the area four years ago); apparently, there's a move to accommodate traffic movement to and from that facility area.  And there's also a planned high-rise due to be constructed in the adjacent tract now occupied by a mobile-home park (same developers), which has heated up the density-vs-existing neighborhood rhetoric in town.  Since Almaden Road is, north of Curtner, a narrow 2-lane winding street (with little room for expansion), I fully expect to see more controversial traffic-pattern manipulation deployed locally in the immediate future.  When the Almaden Expressway was built east of the "old" road in the '60's, it was expected that the old road would devolve into a secondary local server; the planning efforts to utilize that stretch of street for ultra-dense housing has certainly set planners against long-time residents (the local city councilperson who originally opposed the "high-rise" during their campaign but, after being elected to office, reversed their position, is likely to be the subject of a recall petition soon (they've already been by my home twice!).  I think we're just at the beginning of traffic manipulation in the area -- I have no choice but to "keep tuned"; I live here! 

[sparker]

More info on the ever-changing Curtner/Almaden intersection:  Talked to SJ traffic planning; that interchange is an ever-changing "work in progress" to them -- nothing they do seems to satisfy anyone!  Indeed, double-split phasing is the default setting on the signal controls, but they're out there every couple of weeks trying new configurations.  Right now, what they're using is single-directional full-function on E-W Curtner (regular all-movement W followed by regular all-movement E).  N-S (Almaden) starts with double lefts, but segueing to green-ball + green-left NB in the morning, followed by double-green balls N-S and red-lefts; the situation is reversed in the afternoon, with southbound being the recipient of the green ball/green left interim phase. 

Seems SJ traffic planning has finally realized that that short section of (Old) Almaden serves as a shortcut to Bird Avenue, a local N-S arterial that (with a slight jog) empties out onto Old Almaden; it's a viable alternative (although some local Willow Glen residents would demur!) to get to downtown SJ when the Almaden Expressway ramp to NB CA 87 (the next access north of Curtner) backs up, as it is prone to do during morning commute times.  The inverse occurs in the late afternoon.  So SJ traffic planning certainly has their hands full.  Latest talk -- since the EB left-turn lane on Curner has squeezed that street's bike paths down to virtually nothing (prompting very loud and consistent complaints from that quarter!), that dedicated-left lane may not be long for this world! 

Dilemmas such as these -- trying to please as many parties as possible while dodging thrown tomatoes AND attempting to plan things for the foreseeable future -- has given me at least a grudging respect for what some of these folks in traffic planning have to do on an ongoing basis (although I'm not always pleased with some of their agenda-driven activities).  I certainly don't envy them given the current environment in which they function!

[mrsman]

More info on the ever-changing Curtner/Almaden intersection:  Talked to SJ traffic planning; that interchange is an ever-changing "work in progress" to them -- nothing they do seems to satisfy anyone!  Indeed, double-split phasing is the default setting on the signal controls, but they're out there every couple of weeks trying new configurations.  Right now, what they're using is single-directional full-function on E-W Curtner (regular all-movement W followed by regular all-movement E).  N-S (Almaden) starts with double lefts, but segueing to green-ball + green-left NB in the morning, followed by double-green balls N-S and red-lefts; the situation is reversed in the afternoon, with southbound being the recipient of the green ball/green left interim phase. 

Seems SJ traffic planning has finally realized that that short section of (Old) Almaden serves as a shortcut to Bird Avenue, a local N-S arterial that (with a slight jog) empties out onto Old Almaden; it's a viable alternative (although some local Willow Glen residents would demur!) to get to downtown SJ when the Almaden Expressway ramp to NB CA 87 (the next access north of Curtner) backs up, as it is prone to do during morning commute times.  The inverse occurs in the late afternoon.  So SJ traffic planning certainly has their hands full.  Latest talk -- since the EB left-turn lane on Curner has squeezed that street's bike paths down to virtually nothing (prompting very loud and consistent complaints from that quarter!), that dedicated-left lane may not be long for this world! 

Dilemmas such as these -- trying to please as many parties as possible while dodging thrown tomatoes AND attempting to plan things for the foreseeable future -- has given me at least a grudging respect for what some of these folks in traffic planning have to do on an ongoing basis (although I'm not always pleased with some of their agenda-driven activities).  I certainly don't envy them given the current environment in which they function!

Traffic engineers, like most other professionals, often face some kind of conflict amongst their constituencies.  And it is very difficult to keep everyone happy.

[paulthemapguy]

Hennepin Drive at Essington Road in Joliet is another signal that exclusively uses split-phasing.  The north-south legs I understand, because the signal is timed in synchrony with the mall loop signal 1/2 a block to the north.  The east approach has a heavy imbalance toward left-turn movements, but I think it can still be regular phase with protected left turns. 

https://goo.gl/maps/1DmNbsifeno

[Brandon]

Hennepin Drive at Essington Road in Joliet is another signal that exclusively uses split-phasing.  The north-south legs I understand, because the signal is timed in synchrony with the mall loop signal 1/2 a block to the north.  The east approach has a heavy imbalance toward left-turn movements, but I think it can still be regular phase with protected left turns. 

https://goo.gl/maps/1DmNbsifeno

It, and the signal at Ring Road and Essington Road are effectively one signal.  The city (all of these are city streets) decided that it would be best to tie them together to facilitate traffic flow at a very busy entry to the mall.  IMHO, it works great.

[paulthemapguy]

Hennepin Drive at Essington Road in Joliet is another signal that exclusively uses split-phasing.  The north-south legs I understand, because the signal is timed in synchrony with the mall loop signal 1/2 a block to the north.  The east approach has a heavy imbalance toward left-turn movements, but I think it can still be regular phase with protected left turns. 

https://goo.gl/maps/1DmNbsifeno

It, and the signal at Ring Road and Essington Road are effectively one signal.  The city (all of these are city streets) decided that it would be best to tie them together to facilitate traffic flow at a very busy entry to the mall.  IMHO, it works great.

Yeah I know I like it too.  I don't see why they HAD to split the east and west phases though, other than the heavy preference for westbound traffic to turn left onto the south leg.

[Brandon]

Hennepin Drive at Essington Road in Joliet is another signal that exclusively uses split-phasing.  The north-south legs I understand, because the signal is timed in synchrony with the mall loop signal 1/2 a block to the north.  The east approach has a heavy imbalance toward left-turn movements, but I think it can still be regular phase with protected left turns. 

https://goo.gl/maps/1DmNbsifeno

It, and the signal at Ring Road and Essington Road are effectively one signal.  The city (all of these are city streets) decided that it would be best to tie them together to facilitate traffic flow at a very busy entry to the mall.  IMHO, it works great.

Yeah I know I like it too.  I don't see why they HAD to split the east and west phases though, other than the heavy preference for westbound traffic to turn left onto the south leg.

It's so that you can manipulate it with the other intersection at Ring Road.  Otherwise, traffic might back up between Ring Road and Hennepin Drive.

[peterj920]

The intersection of Wis 114 and US 10 is a split phase intersection and works extremely well because US 10 eastbound turns left, and almost all of the traffic turns left.  The oncoming road is a minor street and a lot of times that phase is skipped because there isn't much traffic coming from that part of the intersection.  When the majority of traffic turns left from one leg of an intersection, it can be effective. 

https://www.google.com/maps/@44.2121952,-88.4043398,3a,75y,195.27h,70.54t/data=!3m6!1e1!3m4!1s_FdMm8H4LnCvCPP0vtVPeQ!2e0!7i13312!8i6656