Locations of full and half Continous Flow Intersections

[Revive 755]

Curious has to how many of these intersections have been built, so:

Full

* MO 30 at Summit Road, near Fenton, MO:
http://maps.google.com/maps?hl=en&ie=UTF8&ll=38.504394,-90.457456&spn=0.003619,0.010986&t=k&z=17

* BL 55 at IL 9, Bloomington, IL (this one is confusing to drive through given the proximity of other intersection on IL 9; really could use to be an interchange on BL 55)
http://maps.google.com/maps?hl=en&ie=UTF8&ll=40.488068,-88.952769&spn=0.003517,0.010986&t=k&z=17

Half
* Big Bend at Geyer Road, Kirkwood, MO:
http://maps.google.com/maps?hl=en&ie=UTF8&ll=38.566757,-90.415179&spn=0.001808,0.005493&t=k&z=18

* IL 3 at IL 143, near Wood River, IL:
http://maps.google.com/maps?hl=en&ie=UTF8&ll=38.857823,-90.108565&spn=0.003601,0.010986&t=k&z=17

Other/Mutants

* Business 51 at IL 105, Decatur, IL.  Two of the turning roadways on one side of the cross road:
http://maps.google.com/maps?hl=en&ie=UTF8&ll=39.822801,-88.957983&spn=0.003551,0.010986&t=h&z=17

[Bryant5493]

Haven't seen too many, if any, like that.


Be well,

Bryant

[BigMattFromTexas]

What exactly is a full/half continuous flow intersection, I think I have an idea of what it is from looking at the pictures, but I'm not completely sure......
BigMatt

[UptownRoadGeek]

There's one on Airline Hwy (U.S. 61) in Baton Rouge.

[Revive 755]

What exactly is a full/half continuous flow intersection, I think I have an idea of what it is from looking at the pictures, but I'm not completely sure......
BigMatt

A CFI is an intersection where left turns cross opposing traffic at a signal before the intersection with the cross street.  Right turns from the cross street are aligned so they run parallel to the crossed-over left turns.  For the purpose of this thread, I'm defining a full CFI as an intersection where the left turns are crossed over for both directions of the main street; a half CFI only has left turns crossed over for one direction (there's probably another name for this design, but I can't recall it at the moment - something turning roadway?).

The Maryland site on odd intersections and interchanges has a diagram of a CFI with left turns crossed over on all roadways:
http://attap.umd.edu/UAID_ags.php?UAIDType=5&iFeature=1

[roadfro]

To add on to Revive 755's explanation: The name "continuous flow" comes from the fact that the main intersection and left-turn crossover signals are all coordinated together, such that once the first signal is green, you should be able to flow continuously through the remainder of the intersection without stopping.

The theory behind CFI's is that by putting the left turns on a separate cross-over roadway, it eliminates left turn signal phasing at the main intersection. When working properly, it should drastically reduce delay at the junction because the signal operates in only two phases (as opposed to the eight phases needed to accommodate all lefts and throughs normally).  The drawback to CFI's is a huge right-of-way, higher construction cost, higher maintenance/upkeep cost with the additional signal heads and signs needed, and greater potential for driver confusion.

[froggie]

Adding on to roadfro's comment, another argument used in favor of CFI's (and the one used in the US 61/Baton Rouge case) is that they're cheaper than building an interchange.

BTW, the MD 210/MD 228 junction is an example of a CFI at a 3-way intersection.

[BigMattFromTexas]

Ok, then I'm pretty sure that it's not what I was thinking, and I'm pretty positive that there's none in San Angelo.
BigMatt

[Revive 755]

Found the alternate name for the half CFI design:  "Displaced Left Turn."
http://www.fhwa.dot.gov/publications/research/safety/09056/index.cfm

[Revive 755]

Found a half CFI in Peoria, IL, at the US 150/IL 40 intersection.  This one has the left turn crossover controlled by a yield sign instead of being signalized.
http://maps.google.com/maps?hl=en&ie=UTF8&ll=40.731966,-89.594015&spn=0.003073,0.0103&t=k&z=18
http://maps.google.com/maps?hl=en&ie=UTF8&ll=40.731966,-89.594015&spn=0,0.0103&t=k&z=18&layer=c&cbll=40.731055,-89.593509&panoid=CfmHwslf_tuZqoMKXE_8JA&cbp=12,320.54,,0,7.11

[hm insulators]

To add on to Revive 755's explanation: The name "continuous flow" comes from the fact that the main intersection and left-turn crossover signals are all coordinated together, such that once the first signal is green, you should be able to flow continuously through the remainder of the intersection without stopping.

The theory behind CFI's is that by putting the left turns on a separate cross-over roadway, it eliminates left turn signal phasing at the main intersection. When working properly, it should drastically reduce delay at the junction because the signal operates in only two phases (as opposed to the eight phases needed to accommodate all lefts and throughs normally).  The drawback to CFI's is a huge right-of-way, higher construction cost, higher maintenance/upkeep cost with the additional signal heads and signs needed, and greater potential for driver confusion.

And in this day and age of befuddled drivers, do we really need the greater potential for driver confusion? Today's drivers can't even figure out that red lights mean "STOP" and green lights mean "GO" because they're too busy yapping on their cell phones!

One of the main reasons why I dislike all the new roundabouts that are popping up all over Arizona like weeds except you can't simply spray them with "Round-Up."

[Scott5114]

Arizona like weeds except you can't simply spray them with "Round-Up."

Of course you can't; they're already round

[aztoucan]

Here in Utah Land, UDOT has fallen love with CFI's. They are currently in the process of building 3 more here to the 1 already built at 3500 S and bangerter Hwy

Existing built CFI
http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=3500+south+and+bangerter+&sll=37.0625,-95.677068&sspn=60.806372,134.912109&ie=UTF8&hq=&hnear=Bangerter+Hwy+%26+W+3500+S,+West+Valley+City,+Salt+Lake,+Utah&ll=40.696616,-111.980692&spn=0,0.016469&z=17&layer=c&cbll=40.696619,-111.980808&panoid=a4eLwjceGF_3KPnKPEEPlQ&cbp=12,196.18,,0,5.45

New ones being built
http://www.udot.utah.gov/wego/

They are also in studying other areas in Salt Lake County for places to install these.
http://www.udot.utah.gov/7800South/home.aspx
http://www.udot.utah.gov/main/f?p=100:pg:0:::1:T,V:3029,

[Revive 755]

Found a combination of a CFI and a Michigan left in the Detroit area:
http://maps.google.com/maps?hl=en&ll=42.371128,-83.274382&spn=0.003357,0.008256&t=h&z=18

[pianocello]

Here's a half-CFI in Peoria, IL: http://maps.google.com/?ll=40.731434,-89.592444&spn=0.002785,0.006539&hnear=Davenport,+Scott,+Iowa&t=k&z=18

[Tarkus]

There's actually a sort of a half-CFI in Eugene, Oregon along Franklin Blvd (OR-99) at Agate Street, right near the UO campus.

[kphoger]

I'm feeling too lazy to look for more.  This is just the most recent one I've looked at:

Saltillo, Coahuila
http://g.co/maps/tzcz7

[agentsteel53]

To add on to Revive 755's explanation: The name "continuous flow" comes from the fact that the main intersection and left-turn crossover signals are all coordinated together, such that once the first signal is green, you should be able to flow continuously through the remainder of the intersection without stopping.

The theory behind CFI's is that by putting the left turns on a separate cross-over roadway, it eliminates left turn signal phasing at the main intersection. When working properly, it should drastically reduce delay at the junction because the signal operates in only two phases (as opposed to the eight phases needed to accommodate all lefts and throughs normally).  The drawback to CFI's is a huge right-of-way, higher construction cost, higher maintenance/upkeep cost with the additional signal heads and signs needed, and greater potential for driver confusion.

I am not sure if I understand how this is coordinated to have both continuous-flow, as well as only two phases.

I am guessing that the two phases of the light are "traffic coming from east or west has right of way" and "traffic coming from north or south has right of way".

so, in the east-west situation, let's say eastbound cars want to turn left - northbound.  They cross over the westbound lanes, as their signal is green.  However, the westbound traffic which does not want to turn is coming westbound.  If both have a green light, then we have an intersection with no protected left phase: east-to-north traffic is coming into conflict with westbound traffic.

is this resolved through timing?  i.e. the east-to-north turning traffic is given a head start of several seconds before the westbound non-turning traffic is given green? 

[kphoger]

Here's an animated video that should help you understand the timing (this one has crossovers on all four legs):
http://www.youtube.com/watch?v=6B2NeuXA4lY

[kphoger]

I'm feeling too lazy to look for more.  This is just the most recent one I've looked at:

Saltillo, Coahuila
http://g.co/maps/tzcz7

Oh, and here's the GMSV of the diagrammatic sign that the highway department thought might be useful to westbound traffic.
http://g.co/maps/rbgbq

[cpzilliacus]

Adding on to roadfro's comment, another argument used in favor of CFI's (and the one used in the US 61/Baton Rouge case) is that they're cheaper than building an interchange.

BTW, the MD 210/MD 228 junction is an example of a CFI at a 3-way intersection.

Adam, I believe the eastern end of the Md. 200 (InterCounty Connector) toll road will be a CFI at U.S. 1 (Baltimore Avenue) between Laurel and Beltsville. 

I believe the state was motivated to build an at-grade CFI (instead of a trumpet interchange, perhaps) because the CSX Capital Subdivision tracks run parallel to (and just east of) U.S. 1.   

[Brian556]

There's an incomplete one at Shady Oaks Dr & (Future Spencer Rd) in Denton, Tx
Interesting thing is that the left lanes that are left turn only lanes are open even though there is no street to turn left into.
http://maps.google.com/maps?hl=en&ll=33.203343,-97.097479&spn=0.001495,0.003133&t=h&z=19

[NE2]

There's an incomplete one at Shady Oaks Dr & (Future Spencer Rd) in Denton, Tx
Interesting thing is that the left lanes that are left turn only lanes are open even though there is no street to turn left into.
http://maps.google.com/maps?hl=en&ll=33.203343,-97.097479&spn=0.001495,0.003133&t=h&z=19

That's not a CFI.

[agentsteel53]

Here's an animated video that should help you understand the timing (this one has crossovers on all four legs):
http://www.youtube.com/watch?v=6B2NeuXA4lY

yep, all timing-based.  it just stretches the definition of the word "phase", then.

I'm glad there's a second light at the end of the left-turn "chute" because without it, it would be disastrous if slow-moving traffic did not clear the chute before crossing traffic was released across it.

[roadfro]

There's an incomplete one at Shady Oaks Dr & (Future Spencer Rd) in Denton, Tx
Interesting thing is that the left lanes that are left turn only lanes are open even though there is no street to turn left into.
http://maps.google.com/maps?hl=en&ll=33.203343,-97.097479&spn=0.001495,0.003133&t=h&z=19

That's not a CFI.

More specifically, that is (or will be) a High-T intersection.