In the past we've talked about diamond interchanges with grade separated frontage roads:
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fwww.modot.org%2Fimages%2Fdistricts%2Fstlouis%2F70_94_Interchange.jpe&hash=7c5a97e1fdfe1720a68402604897af6c499d8211)
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fwww.kansascyclist.com%2Fimg%2Fnews%2F95th%2520DDI.jpg&hash=c3cf9c41dc39a016634503ea0912765f5ecc97a6)
But all the ones I've ever seen have a different structure for the frontage road. I was wondering if you know of any where the ramps come in "outside" the frontage road, so the frontage road just abuts the freeway (using the same bridge).
So, for instance, here's half of a diamond interchange with roundabouts to combine the frontage road and ramp at the cross-street intersection:
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi63.tinypic.com%2Fakjpya.jpg&hash=7ce28a12370aa0287a5c5cdf095ab6c3c6573a3e)
You could make that intersection right in right out (RIRO) by taking the frontage road under the cross-street:
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi66.tinypic.com%2F14dmsdh.jpg&hash=83c70319658e8c675d9ade105e29eb8a48f512e7)
From there, you could add an on-ramp to the right side (ala parclo a4) or off-ramp to the left (ala parclo b4) and/or swap the directions of the frontage road between the roundabouts :pan: But anyway, I'm just curious if anyone has seen something along these lines.
Those are all over the place in Arkansas and Texas. Two examples:
http://www.google.com/maps/@35.3656797,-90.2812301,17z
http://www.historicaerials.com/location/33.119905029715675/-95.63375473022461/1964/16 (frontage roads are now one-way)
Quote from: NE2 on March 07, 2017, 08:15:40 PM
Those are all over the place in Arkansas and Texas. Two examples:
http://www.google.com/maps/@35.3656797,-90.2812301,17z
http://www.historicaerials.com/location/33.119905029715675/-95.63375473022461/1964/16 (frontage roads are now one-way)
Those examples don't involve roundabouts.
Quote from: lordsutch on March 07, 2017, 09:37:07 PM
Those examples don't involve roundabouts.
Neither does one of his two separate bridge examples. They're definitely "something along these lines".
Quote from: NE2 on March 07, 2017, 08:15:40 PM
Those are all over the place in Arkansas and Texas. Two examples:
http://www.google.com/maps/@35.3656797,-90.2812301,17z
http://www.historicaerials.com/location/33.119905029715675/-95.63375473022461/1964/16 (frontage roads are now one-way)
Yep, especially in rural areas of Texas.
Here is one I've personally used, in a built-up area of the San Antonio suburbs:
I-35 @ Olympia Pkwy (https://goo.gl/maps/TwZeAwoqvP32)
Quote from: NE2 on March 07, 2017, 10:51:14 PM
Quote from: lordsutch on March 07, 2017, 09:37:07 PM
Those examples don't involve roundabouts.
Neither does one of his two separate bridge examples. They're definitely "something along these lines".
Yeah, I didn't read the OP to indicate that roundabouts were essential to the definition of "interchanges like this." The long description, in fact, is about the bridge structure rather than the intersection type. The handmade illustrations could just easily have been drawn to include right-angle intersections.
Quote from: kphoger on March 08, 2017, 10:32:19 AM
Here is one I've personally used, in a built-up area of the San Antonio suburbs: I-35 @ Olympia Pkwy (https://goo.gl/maps/TwZeAwoqvP32)
I think one-way frontage roads change it into a much more normal interchange. There are certainly examples of those all over, for example: http://www.google.com/maps/@40.7132924,-73.3485558,17z
Thanks! Interesting examples. From here I'll specify two-way frontage roads and buttonhook/hook ramps near the cross street. Whether or not it's a roundabout doesn't matter to me.
The one with two-way frontage roads that I'm familiar with in Texas has undergone reconstruction as part of the I-35 improvements. I don't know if the frontage roads are two-way still or note, but I do know that there is no longer grade separation along the frontage roads. I-35 @ Ross Road used to fit all criteria except for hook ramps.
Quote from: kphoger on March 09, 2017, 10:15:12 AM
The one with two-way frontage roads that I'm familiar with in Texas has undergone reconstruction as part of the I-35 improvements. I don't know if the frontage roads are two-way still or note, but I do know that there is no longer grade separation along the frontage roads. I-35 @ Ross Road used to fit all criteria except for hook ramps.
That reconstruction surprises me a bit, since the secondary-road overpass (Ross Road) over the interstate was changed into an underpass. I'd have thought it would be cheaper to rebuild an old overpass with the same or similar embankments and so on than to build two new ones. How common are things like that in this reconstruction?
Just from observations from GSV, California seems to do that a lot, tying an exit ramp to a parallel surface street. Especially around Los Angeles and the Bay Area.