This was originally to be a post in the Washington [state] thread, but I made it into its own thread because I find it so unusual.
While doing some research on these strange mile-markers (https://mynorthwest.com/634325/weird-sign-explained/) in Washington State (thank you Bruce for the link), I started to look more into the Swamp Creek Interchange, which is the junction of I-405, I-5, and WA-525 in Lynnwood.
Back when it was originally constructed in the 1960s, it was a three-way fully-directional Y-interchange, with a flyover between northbound 405 and southbound 5. However, when the 525 was extended south to meet the Swamp Creek interchange in the early 1980s, the northbound to southbound flyover was removed and replaced with a loop in the northern (northwestern?) corner of the interchange.
From what I can tell, the flyover was single lane, the same as the loop ramp that replaced it. I'm guessing the flyover didn't have much traffic, since traffic using it was already going north on the 405 for quite a while by this point, and largely was proceeding north on 5, rather than south. When the 525 was built to the junction in the early/mid 1980s, that was expected to become a major movement (and still very much is), so the interchange was reconstructed with a major northbound to northbound underpass, and the southbound to southbound ramp was also rebuilt to be on the right side of the freeways, rather than the inside, and runs adjacent to the other underpass to this day.
Here's some before and after images:
(https://live.staticflickr.com/65535/50325316232_667bc938df_z.jpg) (https://live.staticflickr.com/65535/50325141951_35e12f4766_z.jpg)
So, how often have you seen something like this happen? Most of the time, when interchanges are rebuilt to become four-ways from three-ways, the original interchange has already been built to accommodate the extension. This was not the case, despite the original interchange being built less than twenty years before it was reconstructed.
And the loop is largely elevated, negating much of the cost savings of making it a loop.
I wonder if something like that might have happened on the other end of Washington 405. Going southbound there is a weird section where the lanes shift left relative to the concrete panels, and the right-most panel lane ends. (https://goo.gl/maps/kM1PDpwfXxEE218s8) I wonder if the interchange was once designed for the right lane to lead to a flyover to south I-5, but then they decided to put in a loop instead.
Quote from: ErmineNotyours on September 09, 2020, 09:44:39 PM
And the loop is largely elevated, negating much of the cost savings of making it a loop.
I wonder if something like that might have happened on the other end of Washington 405. Going southbound there is a weird section where the lanes shift left relative to the concrete panels, and the right-most panel lane ends. (https://goo.gl/maps/kM1PDpwfXxEE218s8) I wonder if the interchange was once designed for the right lane to lead to a flyover to south I-5, but then they decided to put in a loop instead.
Great observation. Though there are plentiful historic aerial photographs, I see no evidence at any point of there being a flyover planned for that movement. Funny thing is that, if a flyover were needed at that interchange (and it's amazing that it somehow doesn't have anything more than a bunch of terrible inside-to-inside underpasses), it would absolutely be that movement. At this point, as a carpooler, I've taken to using 167 and that new HOV flyover instead of going all the way to I-5, since that whole interchange is just so awful.
The Chestnut/20th intersection off Highway 40 in Downtown St Louis will be replaced by a diamond (https://www.modot.org/i-64-jefferson-interchange/) to 22nd.
Quote from: STLmapboy on September 09, 2020, 10:47:41 PM
The Chestnut/20th intersection off Highway 40 in Downtown St Louis will be replaced by a diamond (https://www.modot.org/i-64-jefferson-interchange/) to 22nd.
There is even a thread about it in the Central States board: https://www.aaroads.com/forum/index.php?topic=25883.0
The land from the cancelled MO 755 Freeway that the old interchange was designed for is being developed into an MLS soccer stadium
I didn't have high expectations for finding an example in Colorado, but the I-25/US 36/I-270/I-76 interchange complex (a distinctively complicated interchange for the state) delivered something like it, specifically in what's now the interchange of I-25, US 36, and I-270 (Google Maps (https://www.google.com/maps/@?api=1&map_action=map¢er=39.827487,-104.982352&zoom=16&basemap=satellite)). For twenty-some years, there was a flyover from present-day US 36 eastbound to I-25 northbound, and the movement is now handled by a loop.
That interchange has gone through several variations as the area highways developed (and produced the broader "˜interchange complex'). It started out as part of a mostly at-grade "Valley Highway extension" from now-I-25 at 70th Ave to the Boulder Turnpike at Federal Blvd. At that point, there was no southeast-to-north movement (1958 topo (https://www.historicaerials.com/location/39.826467782187414/-104.98424695019918/T1958/16); later article with map (https://www.coloradohistoricnewspapers.org/?a=d&d=WMJ19600407-01.2.55&srpos=15&dliv=none)).
When Broadway was grade-separated, slip ramps were added from the existing interchange to complete a diamond there (1964 aerial (https://www.historicaerials.com/location/39.826467782187414/-104.98424695019918/1964/16)). The southeast-to-north flyover came sometime after that, probably in the early 70s, but I didn't find any text references to it (1973 topo (https://www.historicaerials.com/location/39.826467782187414/-104.98424695019918/T1973/16)). A lane was also added to allow traffic from I-76 (then I-80S) to continue onto northbound I-25. (Incidentally, you can see a nasty little weave there to get from I-80S to US 36.)
In the 90s and 2000s, there were a bunch of projects in the area that affected the interchange, including extensions of I-270 and I-76 and bus (later HOT) lanes between I-25 and US 36. The switch from flyover to loop seems most related to making room for the eastbound through movement from US 36 to I-270 (1994 view (https://www.historicaerials.com/location/39.826467782187414/-104.98424695019918/1994/16)), and a left exit from southbound I-25 to eastbound I-270 also now occupies the flyover's "˜level' of the interchange.
As far as traffic volumes go, I don't know but would believe that the eastbound US 36 to northbound I-25 movement is relatively less used than others. (The opposite southbound I-25 to westbound US 36 goes through a signal at the Broadway interchange.) Depending on your trip, it might be more direct to take a surface road between the US 36 area and I-25 instead of going south through the interchange to stay on freeways.
SR 16 & Sprague Ave, Tacoma:
Before:
Full interchange (https://www.historicaerials.com/location/47.23523268727778/-122.46658444404603/1990/16)
After:
Signalized T-intersection (https://www.google.com/maps/@47.2353379,-122.4666795,519m/data=!3m1!1e3)
Here's one that may fit. It's the US-12/BUS US-12 split in Ypsilanti Township, MI. MDOT decided to do this rather than rebuild the bridge.
Before:
(https://i.imgur.com/n4IRBVg.jpg)
After:
(https://i.imgur.com/OONzxzq.jpg)
Quote from: ilpt4u on September 10, 2020, 12:00:22 AM
Quote from: STLmapboy on September 09, 2020, 10:47:41 PM
The Chestnut/20th intersection off Highway 40 in Downtown St Louis will be replaced by a diamond (https://www.modot.org/i-64-jefferson-interchange/) to 22nd.
There is even a thread about it in the Central States board: https://www.aaroads.com/forum/index.php?topic=25883.0
The land from the cancelled MO 755 Freeway that the old interchange was designed for is being developed into an MLS soccer stadium
That's pretty cool to see. I lived in STL for a couple years (on and off) and that interchange always struck me as something designed for something greater. It's replacement with something lower capacity seems more than warranted, as it was always very lightly travelled.
Quote from: ErmineNotyours on September 10, 2020, 12:27:01 AM
SR 16 & Sprague Ave, Tacoma:
Before:
Full interchange (https://www.historicaerials.com/location/47.23523268727778/-122.46658444404603/1990/16)
After:
Signalized T-intersection (https://www.google.com/maps/@47.2353379,-122.4666795,519m/data=!3m1!1e3)
Right in my backyard and I totally forgot about this brilliant example. Weirdly, I think it works better now, since there are two entrance ramps depending on the direction you want to go.
I think I would have thought about it eventually, but I actually changed the thread from being exclusively about "flyovers replaced by loops" to "flyovers replaced by literally anything lower capacity".
Quote from: catch22 on September 10, 2020, 08:44:38 AM
Here's one that may fit. It's the US-12/BUS US-12 split in Ypsilanti Township, MI. MDOT decided to do this rather than rebuild the bridge.
Before:
(https://i.imgur.com/n4IRBVg.jpg)
After:
(https://i.imgur.com/OONzxzq.jpg)
My previous home is just out of frame in the upper left corner of both pictures.
Quote from: Elm on September 10, 2020, 12:06:30 AM
I didn't have high expectations for finding an example in Colorado, but the I-25/US 36/I-270/I-76 interchange complex (a distinctively complicated interchange for the state) delivered something like it, specifically in what's now the interchange of I-25, US 36, and I-270 (Google Maps (https://www.google.com/maps/@?api=1&map_action=map¢er=39.827487,-104.982352&zoom=16&basemap=satellite)). For twenty-some years, there was a flyover from present-day US 36 eastbound to I-25 northbound, and the movement is now handled by a loop.
That interchange has gone through several variations as the area highways developed (and produced the broader "˜interchange complex'). It started out as part of a mostly at-grade "Valley Highway extension" from now-I-25 at 70th Ave to the Boulder Turnpike at Federal Blvd. At that point, there was no southeast-to-north movement (1958 topo (https://www.historicaerials.com/location/39.826467782187414/-104.98424695019918/T1958/16); later article with map (https://www.coloradohistoricnewspapers.org/?a=d&d=WMJ19600407-01.2.55&srpos=15&dliv=none)).
When Broadway was grade-separated, slip ramps were added from the existing interchange to complete a diamond there (1964 aerial (https://www.historicaerials.com/location/39.826467782187414/-104.98424695019918/1964/16)). The southeast-to-north flyover came sometime after that, probably in the early 70s, but I didn't find any text references to it (1973 topo (https://www.historicaerials.com/location/39.826467782187414/-104.98424695019918/T1973/16)). A lane was also added to allow traffic from I-76 (then I-80S) to continue onto northbound I-25. (Incidentally, you can see a nasty little weave there to get from I-80S to US 36.)
In the 90s and 2000s, there were a bunch of projects in the area that affected the interchange, including extensions of I-270 and I-76 and bus (later HOT) lanes between I-25 and US 36. The switch from flyover to loop seems most related to making room for the eastbound through movement from US 36 to I-270 (1994 view (https://www.historicaerials.com/location/39.826467782187414/-104.98424695019918/1994/16)), and a left exit from southbound I-25 to eastbound I-270 also now occupies the flyover's "˜level' of the interchange.
As far as traffic volumes go, I don't know but would believe that the eastbound US 36 to northbound I-25 movement is relatively less used than others. (The opposite southbound I-25 to westbound US 36 goes through a signal at the Broadway interchange.) Depending on your trip, it might be more direct to take a surface road between the US 36 area and I-25 instead of going south through the interchange to stay on freeways.
That's a great example! Exactly what I had in mind when I thought of this thread. It even parallels my example by having the interchange modified from three directions to four directions. Very well found.
The way it's setup now seems more than adequate, especially given the diameter of the east to north loop that was built instead, although I think if done today, that loop might not be ideal given how much redundant land there is within the loop in what is otherwise a relatively urban area (
example of an urban loop designed to accommodate businesses (https://www.google.com/maps/@47.570857,-122.3383275,227m/data=!3m1!1e3)). Then again, fitting in another flyover would have been damn tough without a lot more money. Plus, who knows how busy it is since it's at the "southern" end of the US-36 Freeway, which I know starts way up north-northwest in Boulder (and I doubt many are going all the way south to this point, only to go north on I-25 -- although I understand that plenty of traffic originates south of that point).
Quote from: catch22 on September 10, 2020, 08:44:38 AM
Here's one that may fit. It's the US-12/BUS US-12 split in Ypsilanti Township, MI. MDOT decided to do this rather than rebuild the bridge.
Before:
(https://i.imgur.com/n4IRBVg.jpg)
After:
(https://i.imgur.com/OONzxzq.jpg)
As originally envisioned? No, it would not have fit, since I wanted examples of flyovers replaced by loops.
But, since that is obviously quite unusual, and I wanted more than three replies: yes, this definitely fits, since there can be no doubt the movement now has less capacity than it did before. Classic example, I suspect, of changing traffic conditions no longer warranting such a high capacity ramp. This may have been the case in my original example, and is almost certainly the case of the example in Denver (directly above) as well.
I saw the Swamp Creek interchange when I first discovered Historic Aerials. I was amazed that such an interchange would have been changed as it was. I wonder how a flyover would work with the braiding that was done to interface with 196th St., or why there is no SB-525 to NB-5 or SB-5 to NB-525 movements (which are need). Of course WSDOT has preplanned a lot of things for when things reach capacity at that interchange, so we may see the return of some flyovers in the future.
As for examples, the only thing that seems close that I can quickly recall is I-94 and US 24/Telegraph Rd., being converted from an sweet interlocking left loop interchange into a SPUI.
https://www.historicaerials.com/location/42.2640028799395/-83.26819397196591/2002/16 (Old)
https://www.historicaerials.com/location/42.26471746830239/-83.26849449713622/2010/16 (New)
Quote from: ErmineNotyours on September 09, 2020, 09:44:39 PM
And the loop is largely elevated, negating much of the cost savings of making it a loop.
I wonder if something like that might have happened on the other end of Washington 405. Going southbound there is a weird section where the lanes shift left relative to the concrete panels, and the right-most panel lane ends. (https://goo.gl/maps/kM1PDpwfXxEE218s8) I wonder if the interchange was once designed for the right lane to lead to a flyover to south I-5, but then they decided to put in a loop instead.
I was thinking that it could have been the drop lane for the south I-5 ramp if the bridge was widened.
The ramp from US-8 WB to I-35 SB in Forest Lake, MN was a flyover until last year; it was replaced with a loop ramp last year due to interchange spacing concerns with the next interchange to the south. Satellite (https://www.google.com/maps/@45.2899404,-93.0027674,681m/data=!3m1!1e3)shows the project nearly complete, while Streetview (https://goo.gl/maps/xvYPJC6D12RWB187A)shows the project in earlier stages of construction with the former flyover ramp still intact.
Quote from: EpicRoadways on September 11, 2020, 10:52:37 AM
The ramp from US-8 WB to I-35 SB in Forest Lake, MN was a flyover until last year; it was replaced with a loop ramp last year due to interchange spacing concerns with the next interchange to the south. Satellite (https://www.google.com/maps/@45.2899404,-93.0027674,681m/data=!3m1!1e3)shows the project nearly complete, while Streetview (https://goo.gl/maps/xvYPJC6D12RWB187A)shows the project in earlier stages of construction with the former flyover ramp still intact.
I drove through there in July, it was complete.
The Steve Whalen Blvd flyover on US 35 was rightfully removed in Dayton OH because the route it was suppose to become was cancelled long ago. The flyover went from northbound SW Blvd to US 35 westbound.
https://www.google.com/maps/@39.7546635,-84.1587866,527m/data=!3m1!1e3
Quote from: TEG24601 on September 10, 2020, 05:31:05 PM
I saw the Swamp Creek interchange when I first discovered Historic Aerials. I was amazed that such an interchange would have been changed as it was. I wonder how a flyover would work with the braiding that was done to interface with 196th St., or why there is no SB-525 to NB-5 or SB-5 to NB-525 movements (which are need). Of course WSDOT has preplanned a lot of things for when things reach capacity at that interchange, so we may see the return of some flyovers in the future.
I always wondered about that missing movement. In my head, I've always told myself that there was no way enough traffic was going all the way south on 525 to need to go north on 5, and vice versa. But then, it might be easier to justify not having those ramps if they installed a new interchange at 164th. It could incorporate a bus stop with the Swamp Creek Park and Ride being right there. Community Transit operates several routes at that stop already, and a couple of routes do use 525. But who knows if that transfer was needed at all, or that stop anyways.
Quote from: STLmapboy on September 11, 2020, 10:58:03 AM
Quote from: EpicRoadways on September 11, 2020, 10:52:37 AM
The ramp from US-8 WB to I-35 SB in Forest Lake, MN was a flyover until last year; it was replaced with a loop ramp last year due to interchange spacing concerns with the next interchange to the south. Satellite (https://www.google.com/maps/@45.2899404,-93.0027674,681m/data=!3m1!1e3)shows the project nearly complete, while Streetview (https://goo.gl/maps/xvYPJC6D12RWB187A)shows the project in earlier stages of construction with the former flyover ramp still intact.
I drove through there in July, it was complete.
That's a very interesting example! It almost totally resembles an interchange that is only partially complete. Had you not explained the reasoning for the reconstruction (close proximity to another ramp), I would have assumed the interchange was realigned to support a western extension. I'm guessing that's not the plan?
I think the typical plan for this type of situation would be to installed collector/distributor lanes or another carriageway to allow cars to change lanes without interfering with through traffic. Easiest way would have been to have the off-ramp to Broadway start before the flyover came in, come around the outside of it, and then have the flyover split to allow traffic to exit towards Broadway or continue onto I-35 SB.
Same approach as this interchange (https://www.google.com/maps/@49.2018571,-122.79946,913m/data=!3m1!1e3) in Surrey, BC.
Quote from: BrianP on September 11, 2020, 11:19:11 AM
The Steve Whalen Blvd flyover on US 35 was rightfully removed in Dayton OH because the route it was suppose to become was cancelled long ago. The flyover went from northbound SW Blvd to US 35 westbound.
https://www.google.com/maps/@39.7546635,-84.1587866,527m/data=!3m1!1e3
That was a mighty impressive interchange as originally built. Rare to see an interchange reduced in capacity by that much without there having been an ulterior motive in the original design, such as a freeway (as was the case here).
I think the lack of any protected phase for the left turn from northbound Steve Whalen Blvd to westbound US-35 is fairly telling as to how busy the flyover
wasn't.
The SR 77 stub (42nd Avenue) (https://www.google.com/maps/place/CA-77,+Oakland,+CA/@37.7699177,-122.2230108,537m/data=!3m1!1e3!4m5!3m4!1s0x808f8676a0837db1:0x1daacd6dd2a09351!8m2!3d37.7600795!4d-122.1889099) in Oakland apparently used to have a full freeway interchange at I-880, but was refitted to a diamond in 2011.
2002:
(https://i.imgur.com/muCMxnv.png)
2016:
(https://i.imgur.com/NpSbljL.png)
Quote from: jakeroot on September 11, 2020, 12:31:16 PM
Quote from: BrianP on September 11, 2020, 11:19:11 AM
The Steve Whalen Blvd flyover on US 35 was rightfully removed in Dayton OH because the route it was suppose to become was cancelled long ago. The flyover went from northbound SW Blvd to US 35 westbound.
https://www.google.com/maps/@39.7546635,-84.1587866,527m/data=!3m1!1e3
That was a mighty impressive interchange as originally built. Rare to see an interchange reduced in capacity by that much without there having been an ulterior motive in the original design, such as a freeway (as was the case here).
I think the lack of any protected phase for the left turn from northbound Steve Whalen Blvd to westbound US-35 is fairly telling as to how busy the flyover wasn't.
Thanks to Kurumi's post (https://www.aaroads.com/forum/index.php?topic=27647.0) which led to a post about Dayton's cancelled expressways (https://americascanceledhighways.com/2019/06/27/not-quite-halfway-there-dayton-ohios-i-675-bypass/). Steve Whalen Blvd was to be part of the Southeast Expressway and an early version of I-675. I had heard of the latter but not the former. The Southeast Expressway seems to have evolved into Wilmington Ave.
In Pennsylvania, the I-70/I-79 interchange with U.S. 19 (Murtland Avenue) was downgraded from a cloverleaf to a diverging diamond.
I cheated and used the map of alternative intersections (http://go.ncsu.edu/aii), figuring that some DDI probably replaced flyovers. Didn't find as many as I thought I would:
Kansas: https://www.google.com/maps/d/view?mid=1MMZKi0RdQqjZjtBxmSTznUVnurY&ll=39.10857065868863%2C-94.74183228858857&z=16
Missouri: https://www.google.com/maps/d/view?mid=1MMZKi0RdQqjZjtBxmSTznUVnurY&ll=39.15960056366447%2C-94.50039508518923&z=16
I immeditedly thought of the interchange between Interstate 465 and Sam Jones Expressway on the west side of Indianapolis. The previous interchange had three loops and a flyover ramp for southbound the eastbound traffic while the new interchange is a simple diamond. Since the Indianapolis International Airport terminal moved from near this interchange to the new midfield terminal back in 2008 the down-scaling of this interchange was appropriate. But plenty of traffic still uses this interchange especially in the southbound to eastbound movement which now requires stopping at a traffic light. It's no accident that this is one of the few intersections with three left turn lanes in Indianapolis.
(https://live.staticflickr.com/65535/50332116641_dbc9bd9388_z.jpg)
New interchange on the left, old one on the right.
Quote from: BrianP on September 11, 2020, 04:24:49 PM
Quote from: jakeroot on September 11, 2020, 12:31:16 PM
Quote from: BrianP on September 11, 2020, 11:19:11 AM
The Steve Whalen Blvd flyover on US 35 was rightfully removed in Dayton OH because the route it was suppose to become was cancelled long ago. The flyover went from northbound SW Blvd to US 35 westbound.
https://www.google.com/maps/@39.7546635,-84.1587866,527m/data=!3m1!1e3
That was a mighty impressive interchange as originally built. Rare to see an interchange reduced in capacity by that much without there having been an ulterior motive in the original design, such as a freeway (as was the case here).
I think the lack of any protected phase for the left turn from northbound Steve Whalen Blvd to westbound US-35 is fairly telling as to how busy the flyover wasn't.
Thanks to Kurumi's post (https://www.aaroads.com/forum/index.php?topic=27647.0) which led to a post about Dayton's cancelled expressways (https://americascanceledhighways.com/2019/06/27/not-quite-halfway-there-dayton-ohios-i-675-bypass/). Steve Whalen Blvd was to be part of the Southeast Expressway and an early version of I-675. I had heard of the latter but not the former. The Southeast Expressway seems to have evolved into Wilmington Ave.
Some years back, I had found a blog that had maps of the various proposed expressways for Dayton that were never built...
(Link to the AAroads post, which will have the link to the blog) https://www.aaroads.com/forum/index.php?topic=6879.0
Quote from: jakeroot on September 11, 2020, 12:28:13 PM
Quote from: STLmapboy on September 11, 2020, 10:58:03 AM
Quote from: EpicRoadways on September 11, 2020, 10:52:37 AM
The ramp from US-8 WB to I-35 SB in Forest Lake, MN was a flyover until last year; it was replaced with a loop ramp last year due to interchange spacing concerns with the next interchange to the south. Satellite (https://www.google.com/maps/@45.2899404,-93.0027674,681m/data=!3m1!1e3)shows the project nearly complete, while Streetview (https://goo.gl/maps/xvYPJC6D12RWB187A)shows the project in earlier stages of construction with the former flyover ramp still intact.
I drove through there in July, it was complete.
That's a very interesting example! It almost totally resembles an interchange that is only partially complete. Had you not explained the reasoning for the reconstruction (close proximity to another ramp), I would have assumed the interchange was realigned to support a western extension. I'm guessing that's not the plan?
I think the typical plan for this type of situation would be to installed collector/distributor lanes or another carriageway to allow cars to change lanes without interfering with through traffic. Easiest way would have been to have the off-ramp to Broadway start before the flyover came in, come around the outside of it, and then have the flyover split to allow traffic to exit towards Broadway or continue onto I-35 SB. Same approach as this interchange (https://www.google.com/maps/@49.2018571,-122.79946,913m/data=!3m1!1e3) in Surrey, BC.
Traffic volumes don't support that elaborate of a setup. 35 goes from 4 to 6 lanes at US 8, and I believe most of that traffic coming off 8 stays on I-35, so there's not a problem with weaving or crunches of vehicles trying to get off at Broadway.
Quote from: TheHighwayMan394 on September 11, 2020, 11:15:59 PM
Quote from: jakeroot on September 11, 2020, 12:28:13 PM
Quote from: STLmapboy on September 11, 2020, 10:58:03 AM
Quote from: EpicRoadways on September 11, 2020, 10:52:37 AM
The ramp from US-8 WB to I-35 SB in Forest Lake, MN was a flyover until last year; it was replaced with a loop ramp last year due to interchange spacing concerns with the next interchange to the south. Satellite (https://www.google.com/maps/@45.2899404,-93.0027674,681m/data=!3m1!1e3)shows the project nearly complete, while Streetview (https://goo.gl/maps/xvYPJC6D12RWB187A)shows the project in earlier stages of construction with the former flyover ramp still intact.
I drove through there in July, it was complete.
That's a very interesting example! It almost totally resembles an interchange that is only partially complete. Had you not explained the reasoning for the reconstruction (close proximity to another ramp), I would have assumed the interchange was realigned to support a western extension. I'm guessing that's not the plan?
I think the typical plan for this type of situation would be to installed collector/distributor lanes or another carriageway to allow cars to change lanes without interfering with through traffic. Easiest way would have been to have the off-ramp to Broadway start before the flyover came in, come around the outside of it, and then have the flyover split to allow traffic to exit towards Broadway or continue onto I-35 SB. Same approach as this interchange (https://www.google.com/maps/@49.2018571,-122.79946,913m/data=!3m1!1e3) in Surrey, BC.
Traffic volumes don't support that elaborate of a setup. 35 goes from 4 to 6 lanes at US 8, and I believe most of that traffic coming off 8 stays on I-35, so there's not a problem with weaving or crunches of vehicles trying to get off at Broadway.
But
EpicRoadways just said that it was rebuilt due to interchange spacing concerns. These concerns generally arise when there is too much or too often conflicts between entering and exiting traffic. This would not be a problem if the exit to Broadway is light at best.
If weaving was a concern, they literally could have kept the flyover and built a new ramp around the existing flyover to exit at Broadway. There is no way that would have been more expensive than this huge loop thing they built, which looks more like an unfinished trumpet than something intentional.
Quote from: ari-s-drives on September 11, 2020, 02:22:24 PM
The SR 77 stub (42nd Avenue) (https://www.google.com/maps/place/CA-77,+Oakland,+CA/@37.7699177,-122.2230108,537m/data=!3m1!1e3!4m5!3m4!1s0x808f8676a0837db1:0x1daacd6dd2a09351!8m2!3d37.7600795!4d-122.1889099) in Oakland apparently used to have a full freeway interchange at I-880, but was refitted to a diamond in 2011.
2002:
(https://i.imgur.com/muCMxnv.png)
2016:
(https://i.imgur.com/NpSbljL.png)
That was a pretty tight three-way interchange. Something tells me the new diamond may have similar throughput capabilities :-D
Quote from: Gnutella on September 11, 2020, 04:40:35 PM
In Pennsylvania, the I-70/I-79 interchange with U.S. 19 (Murtland Avenue) was downgraded from a cloverleaf to a diverging diamond.
I'm more looking for examples where flyovers or something close to it were replaced with loops or something else, not necessarily loops to something even lower capacity.
Still, I appreciate the input. Definitely saddens me to see something like that, when there would have been many other options with all those existing loops.
Quote from: johndoe on September 11, 2020, 04:41:35 PM
I cheated and used the map of alternative intersections (http://go.ncsu.edu/aii), figuring that some DDI probably replaced flyovers. Didn't find as many as I thought I would:
Kansas: https://www.google.com/maps/d/view?mid=1MMZKi0RdQqjZjtBxmSTznUVnurY&ll=39.10857065868863%2C-94.74183228858857&z=16
Missouri: https://www.google.com/maps/d/view?mid=1MMZKi0RdQqjZjtBxmSTznUVnurY&ll=39.15960056366447%2C-94.50039508518923&z=16
Both in the same metro area. Interesting. That second one is mighty impressive ... it doesn't even technically exist on Google Maps yet!
Quote from: tdindy88 on September 11, 2020, 09:11:29 PM
I immeditedly thought of the interchange between Interstate 465 and Sam Jones Expressway on the west side of Indianapolis. The previous interchange had three loops and a flyover ramp for southbound the eastbound traffic while the new interchange is a simple diamond. Since the Indianapolis International Airport terminal moved from near this interchange to the new midfield terminal back in 2008 the down-scaling of this interchange was appropriate. But plenty of traffic still uses this interchange especially in the southbound to eastbound movement which now requires stopping at a traffic light. It's no accident that this is one of the few intersections with three left turn lanes in Indianapolis.
(https://live.staticflickr.com/65535/50332116641_dbc9bd9388_z.jpg)
New interchange on the left, old one on the right.
I remember reading about that interchange. This seems to be one of the few that truly doesn't make any sense. Maybe it's not the most major interchange anymore, but it's hard to believe that replacing that huge grade-separated interchange with a diamond will help anyone, really. It doesn't even have any sidewalks. So much for a more urban interchange!
Yeah that Indy one is pretty interesting. I could see them wanting to save bridge costs but the new diamond they installed is pretty beefy! At first I wondered if the flyover had to go because flight paths, but that doesn't seem right. Historic Aerials shows it open for 50 years, I'm impressed that was built so long ago. Wonder if parclo A6 might have been a good fit.
Quote from: jakeroot on September 11, 2020, 11:56:59 PM
Quote from: TheHighwayMan394 on September 11, 2020, 11:15:59 PM
Quote from: jakeroot on September 11, 2020, 12:28:13 PM
Quote from: STLmapboy on September 11, 2020, 10:58:03 AM
Quote from: EpicRoadways on September 11, 2020, 10:52:37 AM
The ramp from US-8 WB to I-35 SB in Forest Lake, MN was a flyover until last year; it was replaced with a loop ramp last year due to interchange spacing concerns with the next interchange to the south. Satellite (https://www.google.com/maps/@45.2899404,-93.0027674,681m/data=!3m1!1e3)shows the project nearly complete, while Streetview (https://goo.gl/maps/xvYPJC6D12RWB187A)shows the project in earlier stages of construction with the former flyover ramp still intact.
I drove through there in July, it was complete.
That's a very interesting example! It almost totally resembles an interchange that is only partially complete. Had you not explained the reasoning for the reconstruction (close proximity to another ramp), I would have assumed the interchange was realigned to support a western extension. I'm guessing that's not the plan?
I think the typical plan for this type of situation would be to installed collector/distributor lanes or another carriageway to allow cars to change lanes without interfering with through traffic. Easiest way would have been to have the off-ramp to Broadway start before the flyover came in, come around the outside of it, and then have the flyover split to allow traffic to exit towards Broadway or continue onto I-35 SB. Same approach as this interchange (https://www.google.com/maps/@49.2018571,-122.79946,913m/data=!3m1!1e3) in Surrey, BC.
Traffic volumes don't support that elaborate of a setup. 35 goes from 4 to 6 lanes at US 8, and I believe most of that traffic coming off 8 stays on I-35, so there's not a problem with weaving or crunches of vehicles trying to get off at Broadway.
But EpicRoadways just said that it was rebuilt due to interchange spacing concerns. These concerns generally arise when there is too much or too often conflicts between entering and exiting traffic. This would not be a problem if the exit to Broadway is light at best.
If weaving was a concern, they literally could have kept the flyover and built a new ramp around the existing flyover to exit at Broadway. There is no way that would have been more expensive than this huge loop thing they built, which looks more like an unfinished trumpet than something intentional.
The driving need for the project was the need to replace the WB 8 bridge over 35. MnDOT decided they could kill two birds with one stone by realigning the ramp to provide more space in between the ramps. The weaving problem wasn't so much the traffic volume as it was the very short spacing...barely 800ft under the old configuration.
Quote from: tdindy88 on September 11, 2020, 09:11:29 PM
I immeditedly thought of the interchange between Interstate 465 and Sam Jones Expressway on the west side of Indianapolis. The previous interchange had three loops and a flyover ramp for southbound the eastbound traffic while the new interchange is a simple diamond. Since the Indianapolis International Airport terminal moved from near this interchange to the new midfield terminal back in 2008 the down-scaling of this interchange was appropriate. But plenty of traffic still uses this interchange especially in the southbound to eastbound movement which now requires stopping at a traffic light. It's no accident that this is one of the few intersections with three left turn lanes in Indianapolis.
I don't agree with the downgrading being appropriate, as Sam Jones makes a nice cut through between I-74 and I-70 (it may be longer but it's not the multi-signal misery of 38th Street between I-465 and I-65). IMHO the free-flow movement from SB to EB should have been kept and the corresponding loop removed at the I-465/I-70 interchange to the south.
Quote from: jakeroot on September 10, 2020, 02:58:55 PM
Quote from: Elm on September 10, 2020, 12:06:30 AMI didn't have high expectations for finding an example in Colorado, but the I-25/US 36/I-270/I-76 interchange complex (a distinctively complicated interchange for the state) delivered something like it, specifically in what's now the interchange of I-25, US 36, and I-270 (Google Maps (https://www.google.com/maps/@?api=1&map_action=map¢er=39.827487,-104.982352&zoom=16&basemap=satellite)). For twenty-some years, there was a flyover from present-day US 36 eastbound to I-25 northbound, and the movement is now handled by a loop. [...]
That's a great example! Exactly what I had in mind when I thought of this thread. It even parallels my example by having the interchange modified from three directions to four directions. Very well found.
The way it's setup now seems more than adequate, especially given the diameter of the east to north loop that was built instead, although I think if done today, that loop might not be ideal given how much redundant land there is within the loop in what is otherwise a relatively urban area (example of an urban loop designed to accommodate businesses (https://www.google.com/maps/@47.570857,-122.3383275,227m/data=!3m1!1e3)). Then again, fitting in another flyover would have been damn tough without a lot more money. Plus, who knows how busy it is since it's at the "southern" end of the US-36 Freeway, which I know starts way up north-northwest in Boulder (and I doubt many are going all the way south to this point, only to go north on I-25 -- although I understand that plenty of traffic originates south of that point).
Whether the loop ramp would be built today is an interesting question. I didn't come by any traffic volumes to guess at whether a case would be made by them there–I may just not know where to search, but maybe because it's technically on I-270, it doesn't seem to have been called out in docs for the US 36 project. I agree space issues would be a significant factor; there's a lot going on in the area transportation-wise, and more to come as the express lane network develops. CDOT wants to do some widening–including, atypically, extending a GPL north of US 36 ("Element 1" here (https://www.codot.gov/projects/i25-us36-104ave-improvements/proposed-action-alternative)), following the addition of the interim I-25 north express lanes that ate up the shoulders. There's also a vision for a direct connection from an I-270 westbound express lane to the I-25 northbound express lane, which would take up some more vertical space and merging area.
--
Following a couple tangents on what warrants a high-capacity ramp:
Related to that interchange, when the US 36 express lane project was under development, CDOT proposed replacing the ramp from southbound I-25 to US 36 that goes through signal with a free-flowing ramp (concepts in Appendix D here (https://www.codot.gov/projects/archived-project-sites/us36eis/documents/us-36-final-eis-technical-reports-and-technical-report-addendums/us-36-feis_traffic-engineering-technical-report.pdf#page=193), starting on pdf's page 193). It seems like a location where they might be able to finagle an elevated ramp over the parking lots, sort of in the spirit of your linked ramp, but the proposals went the route of full property acquisitions. In the end, no changes were made by the project over concerns about loss of access to Broadway; the ramp was left for further study (https://www.codot.gov/projects/archived-project-sites/us36eis/documents/broadway-access-information), and I don't know of the subject being revisited. Funding to buy the properties or build new bridges for whatever ramps probably isn't out there, anyway.
Colorado has another sort of close-quarters 'triangle' of heavy-duty roads at C-470/US 6/I-70, which there are no serious plans to change. (Oh, how I wish they would, or that they had back when there was much less stuff around.) A few years ago, someone sent a question (https://www.thedenverchannel.com/traffic/driving-you-crazy/driving-you-crazy-its-a-conspiracy-why-cdot-hasnt-built-a-ramp-from-6th-ave-to-go-east-on-i-70) to the news about more free-flow access between US 6 and I-70, and the response was that it's not worth the expense.
In the 90s, there was some intention of grade-separating the through movements of US 6 at C-470 (see "Freeways" on page 4 here (https://www.cityofgolden.net/media/pdf_225.pdf#page=4) of the very much outmoded 1992 City of Golden Major Thoroughfare Plan). More recently, a northwest Denver corridor study looked into grade-separating the light rail line at Johnson Rd–there's a priority conflict between the arterial roads and keeping a schedule on the single-tracked rail line–and determined it would be cost-prohibitive.
(And, lastly, speaking of space-hogs, I've wondered if anyone had planned for a loop ramp inside the US 6 to I-70 flyover, but I haven't found anything to suggest other movements have been sketched out.)
The Swamp Creek interchange really should have included a SB I-5 to NB SR 525 ramp, with braided access to Alderwood Mall Blvd. As it stands, a lot of backtracking is required to reach the mall.
Quote from: Bruce on September 16, 2020, 05:37:26 AM
The Swamp Creek interchange really should have included a SB I-5 to NB SR 525 ramp, with braided access to Alderwood Mall Blvd. As it stands, a lot of backtracking is required to reach the mall.
The access issues with Alderwood Mall do remind me a lot of the issues with Southcenter Mall, at the southern end of 405. It's easy to get off northbound 5 to access Southcenter, but getting back on to northbound 5 requires some looping around onto Southcenter Blvd. Southbound has the issue for access: either get off at Southcenter Blvd, and loop around over the 405 to access the mall, or get on to 405 and exit at West Valley Hwy (WA-181). You can even go west and loop onto 51st Ave S, go over 518, and then stay on that as it becomes Klickitat Dr which ends at the mall. Either way, not exactly direct.
The big issues seems to be the separation between the on and off ramps. They are in totally different places depending on where you are coming from and/or going to, so there's a lot of traffic that seems to be wandering around trying to figure out where the opposite ramp is from the one they used to get to the mall. At least the Alderwood interchanges are complete (apart from 5/525/405).
Still, it's all better than Alderwood, though, since at least there are interchanges in the rough vicinity. Seems like the interchanges for Alderwood Mall were designed after the fact, or there was little consideration of how traffic actually moves in the area. The fact that Alderwood Mall Pkwy passes over I-5 to the south without any freeway access is surprising to me. Not now, but maybe 20 years ago, it could have been considered for maybe an on or off-ramp. Or at the very least, yeah, there should have been access between southbound 5 and northbound 525.