Favorite intersection type?

[hotdogPi]

Functionally, it seems identical to a hamburger roundabout:

Why is movement B allowed? Removing movement B would remove all left turns.

[tradephoric]

I just read the Utah Department of Transportation is planning to convert Bangerter Highway into a Freeway.  This is interesting since 7 CFIs have been built along Bangerter Highway over the past half dozen years.  The CFI at Bangerter Hwy and 5400 cost nearly 10 million dollars to build in 2010 and now UDOT is proposing a 60 million grade separated interchange slated for construction in 2017.  Only getting 7 years of life out of an innovative intersection that cost nearly 10 million dollars to build doesn't seem like a very wise investment.  The concrete alone has 15 years of useful life left in it. 

http://www.westjordanjournal.com/2016/04/08/107510/bangerter-highway-to-transform-into-freeway

[kphoger]

"Town center intersections", which is just a fancy way of saying one-way pairs.

[doorknob60]

To get things started, a parallel flow intersection is being proposed at the US 41 / SR-54 intersection in Land "˜O Lakes, Florida.  I like the fact that it eliminates direct left turns, but OTOH it looks like a total monstrosity!  I don't know if I should love it or hate it...

That's like a ridiculous souped up (though also different) version of a proposed intersection to be used in a few spots on US-20/26 from Meridian and Boise to Caldwell. (Oh boy does the highway really need widening, most of it is only 2 lanes).

[kphoger]

I also like this intersection/interchange design, even though I'm not sure it fits the topic, being that it's not signalized.  It keeps traffic moving on both streets, and if you want to turn left, you turn around and then turn right, like a Michigan left.

That's just a roundabout under an overpass, grade-separated as an interchange.

[tradephoric]

Here was the Detroit Rapid Transit Commission's vision of a grade separated intersection in the 1920s.  They called them "super-highways"  and examples include 8 Mile, Telegraph, Woodward, and Northwestern.  These "super-highways" still functioned as surface streets but would be grade separated at major cross-streets.


The reality is very few grade separated interchanges were built along these super-highways.  Here's a grade-separated interchange that was built at Woodward & 8 Mile in 1956.  As you can see they squeezed out the rail lines from the final design.  Interestingly, the last streetcar to run down Woodward was on April 8, 1956, the same year this interchange was completed


This picture from 1954 shows the very start of construction at the interchange.

[cl94]

I don't have SYNCHRO on my personal computer to check it myself, but could you run crazy high opposing left turn volumes in there to see what happens? I'd love to see that.

I found 2012 peak hour counts on page 4-15 of the Draft Preliminary Engineering Report for this project:
http://active.fdotd7studies.com/sr54/us41-at-sr54/wp-content/uploads/pdf/Draft_PER_Revised111015withAppendices.pdf

I plugged in these counts into SYNCHRO and recreated the model.  It still seems to be holding its own with all approaches clearing in one cycle (but i did have to add dedicated left turn lanes to prevent left-turning traffic from queuing up in the box). 

https://www.youtube.com/watch?v=TFQQp1Dy24s

Just got back to this thread and saw this. Looks like it would work. Wow.

[tradephoric]

^Another option is a design similar to the Silver Springs, Maryland intersection.  Would require less ROW as only one of the roadways would have to widen out.


https://www.google.com/maps/@39.02017,-77.01275,17z/data=!3m1!1e3

[tradephoric]

Here's a concept for a Michigan Left / roundabout intersection.  The problem with this design is people in the E/W direction would also be using the roundabouts to make a U-turn to continue in the N/S directions.  Drivers wouldn't have much time to merge into the right most lane to complete their "left turn". 

[jeffandnicole]

Here's a concept for a Michigan Left / roundabout intersection.  The problem with this design is people in the E/W direction would also be using the roundabouts to make a U-turn to continue in the N/S directions.  Drivers wouldn't have much time to merge into the right most lane to complete their "left turn". 

In most states, it's illegal to turn from the right lane to the left lane.  You're supposed to turn from the right-most lane to the right-most lane.

While everyone does such a maneuver above, that's part of the difficulty in designing such concepts.  Something that may work in theory isn't always legal.

[tradephoric]

In most states, it's illegal to turn from the right lane to the left lane.  You're supposed to turn from the right-most lane to the right-most lane.

^I agree.  Some states may be hesitant to try certain innovative intersections because of the laws on the books.  Of course i think people would adapt.  Michigan has the flashing red ball permissive left turn.  While technically illegal, it's an unwritten law in Michigan that drivers are allowed to roll through a blinking red at permissive lefts. 

[tradephoric]

A quadrant intersection works pretty well for that Land O'Lakes intersection too.  There is a heavy WB left turn movement during peak hour which causes EB through traffic to come to a soft stop, but not horrible.  If FDOT was willing to built two quadrants on the SE & NW corner, it would function quite nicely. 

https://www.youtube.com/watch?v=uoQP1rcrzbc

The one thing i don't like about FDOT's PFI proposal is that it's just a vast area of asphalt.  Sure, it might be extremely effective at moving vehicles through the intersection, but you got to pave an entire city block to accomplish it.  A quadrant intersection is essentially a spread out PFI but it allows the opportunity for commercial development in the middle of the intersection.  Here's an example of commercial development within the quadrant intersection at Telegraph & Maple in Bloomfield Hills, Michigan:

[johndoe]

In most states, it's illegal to turn from the right lane to the left lane.  You're supposed to turn from the right-most lane to the right-most lane.

You are turning to the nearest lane, but then making two lane changes left   I've always wondered about that ; is there a rate of legal lane changes ? 

The Other way to look at it is that you're supposed to turn into the nearest lane going to your destination...that driver IS turning to the nearest left turn lane.

[kphoger]

you're supposed to turn into the nearest lane going to your destination.

[citation needed]

[jakeroot]

you're supposed to turn into the nearest lane going to your destination.

[citation needed]

Not sure exactly what the law says, but if the law were mine to write, you'd be allowed to turn into the farthest lane IF you are in the center-most turn lane (should that apply), AND your "destination" is within an unreasonably short distance of the intersection.

To be clear, I have no idea what the law is for each state, but at least in my opinion, turning into the farthest lane should be okay if both of the above factors were true.

[johndoe]

[citation needed]

That's fair; quoting what I was told in driver's ed class isn't quite good evidence   To be honest I don't know the laws, but that's how some roads are designed.  Your profile says you're from Kansas, so I picked a random example.  Consider the eastbound (EB) approach here: https://goo.gl/maps/pTGo3adkLnA2

For right turns, if you don't want to end up on WB College Blvd you're not going to turn to the immediate lane.  For left turns, if you don't want to end up on WB I435 you're not going to turn to the immediate lane.  The lefts seem more obvious...it's very common at diamond interchanges.  For the rights, as the distance between intersections goes down the odds of people turning to the first lane and weaving goes down.  This example is decently long, but I'm sure there are better examples where the auxiliary right turn lane is really short.

[jeffandnicole]

In most states, it's illegal to turn from the right lane to the left lane.  You're supposed to turn from the right-most lane to the right-most lane.

You are turning to the nearest lane, but then making two lane changes left   I've always wondered about that ; is there a rate of legal lane changes ? 

I guess if you want to be completely by the books, you would turn from the right lane to the right lane.  Then signal to turn into a lane.  In most states, there's a distance required to signal, such as 100 feet.  After than 100 feet, then you can merge left.  In this case, you would have to merge into the center lane, signal for another 100 feet, then merge into the left lane.

Can you do that in the space provided in the hypothetical example above?  Actually, yes...it appears there's time to do that.

Does anyone do that?  No.  And it would look ridiculous if they did. 

[tradephoric]

https://www.google.com/maps/@39.8678959,-82.9349983,503m/data=!3m1!1e3

This is a RCUT intersection but instead of forcing side-street traffic to make a u-turn, they built a flyover ramp instead (and they threw in a few roundabouts for good measure). 

[tradephoric]

Here's a few examples of offset T-intersections.  The are essentially offset RCUT intersections.  These intersections allow the main-drag to maintain good signal progression. 


https://www.google.com/maps/@42.557264,-83.2857964,703m/data=!3m1!1e3


https://www.google.com/maps/@42.5280794,-83.356252,349m/data=!3m1!1e3

[kphoger]

In most states, it's illegal to turn from the right lane to the left lane.  You're supposed to turn from the right-most lane to the right-most lane.

You are turning to the nearest lane, but then making two lane changes left   I've always wondered about that ; is there a rate of legal lane changes ? 

I guess if you want to be completely by the books, you would turn from the right lane to the right lane.  Then signal to turn into a lane.  In most states, there's a distance required to signal, such as 100 feet.  After than 100 feet, then you can merge left.  In this case, you would have to merge into the center lane, signal for another 100 feet, then merge into the left lane.

Can you do that in the space provided in the hypothetical example above?  Actually, yes...it appears there's time to do that.

Does anyone do that?  No.  And it would look ridiculous if they did. 

I do this whenever possible.  For example, this is a common perspective on the way to my house.  At the very next side street, I turn right.  Do I immediately enter the right lane?  No, I enter the left lane, engage my right turn signal, then move right as gradually as possible (which is not very gradual in this instance).  Similarly, at this location nearby, most people turning from the right need to move left to get on the main highway.  I do not do this:  I enter turn into the right lane, then signal my lane changes over into the left lane.

But that's just practice.  My point was that the law doesn't say your "supposed to" turn into any lane except the nearest one.  Depending on the state, it either says you have to use the nearest one or it doesn't restrict which lane you use at all.

[johndoe]

...grade separated RCUT ...

Cool, I haven't seen that one before.  I've seen it paired with a normal diamond and a SPUI, here's the first time I've seen it with a DDI:

Time lapse camera: http://www.earthcam.net/projects/kdot/jocogateway/?cam=mpc3
Actually this one just opened today!

[tradephoric]

...grade separated RCUT ...

Cool, I haven't seen that one before.  I've seen it paired with a normal diamond and a SPUI, here's the first time I've seen it with a DDI:

Time lapse camera: http://www.earthcam.net/projects/kdot/jocogateway/?cam=mpc3
Actually this one just opened today!

Wow!  I'm going to have to study this for the next half hour now to figure out how to navigate it.  It's probably not that bad driving it but it looks like spaghetti junction from the air!

[johndoe]

Wow!  I'm going to have to study this for the next half hour now to figure out how to navigate it.  It's probably not that bad driving it but it looks like spaghetti junction from the air!

Now this is REALLY cool...drone view!
https://www.youtube.com/embed/EvoLxMTc8Kg

[tradephoric]

Here's a PFI folded diamond interchange concept.  I'm seeing more of these proposed but has one actually been built yet?  According to the description in the video ODOT has decided to build a SPUI instead.

https://www.youtube.com/watch?v=7F-RvFyXWlA

[CNGL-Leudimin]

Any intersection the good old Kurumi's Me and the Roads wouldn't allow to build .