How to braid two (or more) interchanges... correctly.

[SoDakInterstateEnthusiast]

Sometimes (okay, all the time), I like to play around with creating fictional freeway alignments and engineering the interchanges for them. Among my favorite things to do is to take a South Dakota city on Google My Maps, and just engineer a freeway system around it pretending it's a big city. I don't know why.

Well, while practicing some interchange braiding... it came to my attention that I am really, really bad at it. Like really. Every time I try to combine access for two roads that are relatively closer together, I screw the geometry up and it just ends up looking like a nightmare to drive on. So I figured I'd ask... the people who actually know... for a little guide on interchange braiding.

What I'm looking for is:

- How to braid two local-road interchanges
- How to braid a system interchange and local-road interchange
- How to compact the braids in a way that would still be reasonable to fit bridge structures yet not take up too much land around the freeway
- If it is okay to braid directly to a fly-over ramp (although that probably wouldn't happen to begin with because that would be one expensive bridge structure)

I'm open to real-world examples, or your own drawings if you want to model an ideal situation for teaching! However, if you do post a real-world example(s), I would prefer that it's a Google Maps link as opposed to an embedded image since for some reason I can not always see the embedded images.

I look forward to learning how to do this properly and no longer look like an idiot!

Thank you!

[NE2]

Check out I-4 at Disney World for a good example where there is no access between adjacent interchanges.

[SoDakInterstateEnthusiast]

Check out I-4 at Disney World for a good example where there is no access between adjacent interchanges.

Are you saying that they don't (and should) have a connecting ramp from the flyover ramp of that cloverleaf to the off-ramp that leaves the freeway before the flyover merges on?

[SkyPesos]

Look at I-270 exits 30-33. I think it's pretty good example for braiding, though there's a unique situation to that one, like with most interchange designs. There's one freeway-freeway interchange (exit 30), and two freeway-arterial interchanges (32 and 33) as part of it.

[SoDakInterstateEnthusiast]

Look at I-270 exits 30-33. I think it's pretty good example for braiding, though there's a unique situation to that one, like with most interchange designs. There's one freeway-freeway interchange (exit 30), and two freeway-arterial interchanges (32 and 33) as part of it.

Thanks! The I-270/US-62 interchange just south of these for sure answers one of my questions - it does have another ramp coming directly off the flyover. I figured that could be done, just wondering if that's a thing that is recently shunned on freeways for safety reasons sort of like how cloverleafs are discouraged in higher-traffic areas.

As with the actual exits 30-33, if I'm not mistaken, what I noticed with the setup there is that the 6 lanes seem to deviate into two sets of 3 lanes, and then those sets of lanes sort of take turns having exits, at least NB. So if you knew what exit you wanted to take ahead of time, you'd pick the set of lanes you wanted in order to take that exit. Unless I'm analyzing this incorrectly.

[ran4sh]

For an example of how not to do it, look at the northbound side of I-85 in Georgia from exit numbers 104 to 109. There are several ramps that lead to the C-D roadway, but only one ramp that enters the mainline from the C-D roadway, before the end of the C-D roadway. And only traffic entering from interchange 104 can use it. That means traffic entering from interchanges 106, 108, and 109, have no choice but to remain on the C-D roadway all the way to the end, where it merges into one lane before merging into the mainline lanes.

When I am in that area, I frequently go out of my way to enter I-85 north at interchange 107, because the onramp enters the mainline instead of the C-D roadway.

The southbound side of the same route is better, I have no issue with it.

[SkyPesos]

Look at I-270 exits 30-33. I think it's pretty good example for braiding, though there's a unique situation to that one, like with most interchange designs. There's one freeway-freeway interchange (exit 30), and two freeway-arterial interchanges (32 and 33) as part of it.

Thanks! The I-270/US-62 interchange just south of these for sure answers one of my questions - it does have another ramp coming directly off the flyover. I figured that could be done, just wondering if that's a thing that is recently shunned on freeways for safety reasons sort of like how cloverleafs are discouraged in higher-traffic areas.

As with the actual exits 30-33, if I'm not mistaken, what I noticed with the setup there is that the 6 lanes seem to deviate into two sets of 3 lanes, and then those sets of lanes sort of take turns having exits, at least NB. So if you knew what exit you wanted to take ahead of time, you'd pick the set of lanes you wanted in order to take that exit. Unless I'm analyzing this incorrectly.

For the C/D lanes, they serve the Easton and OH 161 exits (33 and 30) NB, while the mainline serves Morse (32). This means if you got onto I-270 from Morse, you can't access the OH 161 or Easton Rd ramps, which isn't an issue as one of the mall's entrances is at Morse, and there's plenty of surface road options to get from Morse to 161. I like this setup, as it takes the 670-161 traffic (pretty common as I-670 is the main route to downtown Columbus and New Albany is a growing suburb of the area) off the I-270 mainline, which is crowded by itself at times.

The lane split on I-670 to I-270 North was added about a year ago. Those lanes had you choose whether you wanted to go onto I-270 North, or Easton/OH 161 before you exited off I-670, to minimize weaving on the section of I-270 between I-670 and the Easton/161 C/D lane exit. ODOT has been adding these types of lane splits in a few places recently, with another example in Columbus from I-270 South to US 33 West and Avery-Muirfield Dr.

[webny99]

I'm not sure if this counts as "braiding", but the Can of Worms interchange (junction of I-490, I-590, NY 590, and several local roads) near Rochester used to be two directional-T interchanges and was rebuilt in the late '80's as one single interchange.

Additional references:
http://www.empirestateroads.com/week/week1.html
https://en.wikipedia.org/wiki/Can_of_Worms_(interchange)

[SoDakInterstateEnthusiast]

I'm not sure if this counts as "braiding", but the Can of Worms interchange (junction of I-490, I-590, NY 590, and several local roads) near Rochester used to be two directional-T interchanges and was rebuilt in the late '80's as one single interchange.

Additional references:
http://www.empirestateroads.com/week/week1.html
https://en.wikipedia.org/wiki/Can_of_Worms_(interchange)

I don't think that would technically be braiding. The interchange - what with I-590 mainline traffic no longer being conducted to a concurency and rather conducted straight under I-490 (if what the original configuration of this interchange is what I'm imagining based on what you said) - is basically a complete 4-way interchange now instead of two 3-ways. They're not braided into each other, they're just consolidated to one now. However, East Ave and Highland Drive get access to I-490 SB, so at the very least there's access for another road tied into this system interchange, although not a complete interchange. (Would that count as a "braid"?)

EDIT: I-490 WB gets access to University Ave as well, so that's another access point for another road tied into this interchange.