Forgive me if this has been discussed here before, but are there any examples of a freeway to freeway roundabout/circle interchange? I was looking at the interchange between I-476 US-1 in Media (http://goo.gl/maps/ciWQ), and if you squint enough, it does sort of look like a boxy circle. That got me wondering if dumping all those ramps into one large roundabout/traffic circle might serve just as well or better than several signaled intersections.
http://en.wikipedia.org/wiki/Roundabout_interchange#Three-level_stacked_roundabout
Duh. I even read that page. Not sure how I missed that section. So I wonder what the capacity between that interchange (three-level stacked diamond?) and a similar sized stacked roundabout would be.
Does I-587/NY 28/I-87 count?
Quote from: deanej on April 03, 2011, 12:54:54 PM
Does I-587/NY 28/I-87 count?
As a roundabout freeway-freeway interchange, yes. Not quite a three-level roundabout, though. Some would argue that a roundabout means you're not on a freeway, but you have cases like the end of MA 213 where you can use the ramps to make a U-turn, so it's iffy.
How about the new I-35 to US 50 Interchange near the KS Turnpike in Emporia, KS? Google maps shows that as one as part of a new interchange with the KTA reversing the trumpet that was there since the pike openied.
Would this count? http://maps.google.ca/?ll=45.447065,-73.742058&z=16
Quote from: NE2 on April 03, 2011, 01:58:34 PM
Quote from: AlpsROADS on April 03, 2011, 01:55:48 PM
Quote from: NE2 on April 03, 2011, 01:49:31 PM
Quote from: deanej on April 03, 2011, 12:54:54 PM
Does I-587/NY 28/I-87 count?
No.
Because?
Because the original poster is asking about a different thing.
Agreed. I was talking about two freeways crossing each other with a third level roundabout where all the off/on ramps dump into/come out of.
There's a good example in the Wikipedia article: http://goo.gl/maps/cQug
Now neither Causeway Blvd or US61 are technically freeways, but for the purposes of example, they are when they cross each other. This just seems like an interesting solution to traditional freeway-freeway interchanges, and should be more free-flowing than the three-level diamond I mentioned above. OTOH, people in the US have issues respecting yield signs, so who knows if it's really any better. Also, I could see cases where there's so much traffic off one or more of the ramps where the roundabout would become gridlocked. I guess you can make it wider to handle more traffic, then you have a bunch of weaving, though at least the weaving is out of the mainline traffic. Look kids! Big Ben! Parliament!
Quote from: Dr Frankenstein on April 03, 2011, 03:54:20 PM
Would this count? http://maps.google.ca/?ll=45.447065,-73.742058&z=16
Not quite. In that case 520 is actually entering the roundabout. I was referring to a roundabout which was a separate level over/under the two roadways crossing each other. Only the ramps would enter it.
Quote from: roadman65 on April 03, 2011, 03:48:52 PM
How about the new I-35 to US 50 Interchange near the KS Turnpike in Emporia, KS? Google maps shows that as one as part of a new interchange with the KTA reversing the trumpet that was there since the pike openied.
That looks sort of like a dumbell interchange... though it's more like they decided to use a couple of roundabouts instead of two trumpets via an access road? That's... strange. Though it looks like it was (or is becoming?) something different....
Getting back to the original question.
Of course, the original interchange mentioned is a "volleyball" interchange and has traffic lights at each corner.
http://www.kurumi.com/roads/interchanges/volleyball.html
http://maps.google.com/?ie=UTF8&t=h&ll=39.937617,-75.362497&spn=0.001847,0.004769&z=18&layer=c&cbll=39.937617,-75.362497&panoid=aTN2om0q_58eXHTle8nHGg&cbp=12,243.84,,0,0
Boy, this interchange brings back memories...I had an accident in a rental car two years ago at the very intersection you posted (I-476/US 1)...trying to turn left onto northbound US 1 from I-476, individual in front of me starts to pull out, then STOPS just as I move forward at about 5/10 MPH. BANG.
Fortunately I had bought the damage waiver from Enterprise, but it was a bummer to a fine Christmas holiday.
The junction of the M4 and M32 near Bristol uses a roundabout, but it's not a three-level interchange (or "roundabout stack," maybe?). Instead, the M32 ends (or begins) at the M4 and it becomes a roundabout to which the ramps to and from the M4 connect.
The volleyball interchange of I-395 and Seminary Road in Virginia is probably the closest I've seen, but it's definitely not a roundabout. It's got lights at all four corners. I'd wager that 99% of the people who use it are unaware the left on red is legal at all four lights because you're going from a one-way street to another one-way street (doesn't matter that the "street" in part of an interchange).