The "Illinois Diamond"

[CapeCodder]

I've only seen diamond interchanges like this in Illinois. Missouri didn't really have many of them.

An Illinois Diamond is a diamond interchange that has the exit ramps bow out a bit of a distance, whereas the entrance ramps are short. They are prevalent on most of Illinois' interstates.

[wanderer2575]

You mean something like this?  https://goo.gl/maps/ANWLfQqYEWK2
(US-127 east of Shepherd, MI)

[CapeCodder]

You mean something like this?  https://goo.gl/maps/ANWLfQqYEWK2
(US-127 east of Shepherd, MI)

Yes. They must be relatively older than the diamonds I've seen in MO. Those diamonds are compact.

[pianocello]

Where in Illinois is this prevalent? I know the interstates of the northern half of the state fairly well, and I can't think of anything like the Michigan example cited.

[CtrlAltDel]

Do you mean something like this?

https://www.google.com/maps/@41.2890996,-88.2319511,627m/data=!3m1!1e3

[DandyDan]

Do you mean something like this?

https://www.google.com/maps/@41.2890996,-88.2319511,627m/data=!3m1!1e3

If that's what he's talking about, that seems like a byproduct of the diagonal nature of one of the roads in the interchange more than anything. It don't look like that happens when the roads are perpendicular.

[CapeCodder]

Do you mean something like this?

https://www.google.com/maps/@41.2890996,-88.2319511,627m/data=!3m1!1e3

Yes, I've seen them on 55, 64, 70, and 72. 57 has a few of them, but not that many.

[CapeCodder]

Here is an example from 55 in Staunton, IL:
https://www.google.com/maps/@39.0184371,-89.7470407,15.83z

[NE2]

Here is an example from 55 in Staunton, IL:
https://www.google.com/maps/@39.0184371,-89.7470407,15.83z

They all look the same length to me...

[ET21]

They all look the same to me... 

[sparker]

I've seen quasi-diamond configurations like this in numerous locations, particularly when a straight-ahead movement from the offramp leads to a road (frontage or otherwise) with some traffic attractant located on it.  Approaching Delano, CA NB on CA 99, a ramp such as this segues directly into the old US 99 route through town, previously "Business 99"; the return on-ramp to CA 99 was originally located between the old alignment (which curves through a RR underpass) and the freeway overpass on the E-W road crossing at that point.  A few years ago the configuration was realigned:  the NB on-ramp now diverges from the approach to the underpass north of the crossing road, while the SB direction of former Business 99 is now turned back north on a cul-de-sac loop.  Effectively, there is no through bidirectional business route at this time.     

[jakeroot]

Here is an example from 55 in Staunton, IL:
https://www.google.com/maps/@39.0184371,-89.7470407,15.83z

The layout seems to leave room for possible conversion to cloverleaf operation in the future. I know Illinois has quite a few of those dreaded cloverleafs.

[JoePCool14]

Here is an example from 55 in Staunton, IL:
https://www.google.com/maps/@39.0184371,-89.7470407,15.83z

The layout seems to leave room for possible conversion to cloverleaf operation in the future. I know Illinois has quite a few of those dreaded cloverleafs.

Yup, IDOT has quite the admiration of cloverleaves. Sometimes they use them on such busy interchanges it can make for some dangerous merges.

[hotdogPi]

Here is an example from 55 in Staunton, IL:
https://www.google.com/maps/@39.0184371,-89.7470407,15.83z

The layout seems to leave room for possible conversion to cloverleaf operation in the future. I know Illinois has quite a few of those dreaded cloverleafs.

Yup, IDOT has quite the admiration of cloverleafs. Sometimes they use them on such busy interchanges it can make for some dangerous merges.

So does MassDOT: 93/495, 2/495, 290/495 (almost), 95/495 (south of Boston), 24/495,  2/95/128, and 93/95/128 (north of Boston). That's all of the 4-way freeway junctions that don't involve the Mass Pike.

[Paulinator66]

Yup, IDOT has quite the admiration of cloverleafs. Sometimes they use them on such busy interchanges it can make for some dangerous merges.

Actually, they USED to like the cloverleaves (leafs?). When most of the original interstates were built (1950s and 60s) that was the preferred way to build them but now, with traffic counts rising, the cloverleaves present a merging/weaving problem and I know that IDOT does not build them any more.  In fact, I55 around Bloomington recently had a complete tearout and rebuild and their cloverleaves have all been altered to avoid the merging problem.  Further, IDOT is in the final planning stages for a complete tearout and rebuild around Springfield and their cloverleaves will all be the "Illinois Diamond" discussed here earlier. . .although this concept is from from an Illinois-only thing.  It's the "new" normal.  Look at I70 or I44 in MO. . .almost all diamonds.

[jakeroot]

Yup, IDOT has quite the admiration of cloverleafs. Sometimes they use them on such busy interchanges it can make for some dangerous merges.

Actually, they USED to like the cloverleaves (leafs?). When most of the original interstates were built (1950s and 60s) that was the preferred way to build them but now, with traffic counts rising, the cloverleaves present a merging/weaving problem and I know that IDOT does not build them any more.

IDOT rebuilt the 55/80 interchange back in 2005 with ... another cloverleaf. Maybe that was before they decided to dump cloverleafs, but it's surprising to see an entire rebuild that basically just improves movement speeds but hardly improves capacity. A couple of flyovers would help the most.

[ilpt4u]

Until IDOT gets rid of the I-55/I-80 and (with the help of ISTHA) I-90/I-290/IL 53 Cloverleafs...I question any efforts they have made to eliminate them.

The I-280/I-74/I-80 "Fist Bump," I-74/I-280/US-6, and I-80/I-88/IL 92/IL 5 Cloverleafs in the Quad Cities need gone, too

There is probably enough Truck Traffic on I-39 now to dump the Cloverleafs for I-39/I-80 and I-39/I-88

And since I-57/I-74/I-39 functions as a North/South Chicago Bypass Route (Since I-39 never was completed down to Salem, and probably never will be now), the Cloverleaf @ I-57/I-74 in Chambana needs to go too

[cl94]

New York has a handful of those things. First one that comes to mind is in PETA's favorite town-Fishkill. There's a variation at NY 135's interchange with NY 107. I-81 has one that is like this on the NB side in Cortland.

[JoePCool14]

Until IDOT gets rid of the I-55/I-80 and (with the help of ISTHA) I-90/I-290/IL 53 Cloverleafs...I question any efforts they have made to eliminate them.

The 90/290/53 one is particularly bad. First hand have had issues merging. It doesn't really seem to me like IDOT has been taking serious initiative to remove them. Maybe it's a District 1 thing mainly these days.

[kalvado]

New York has a handful of those things. First one that comes to mind is in PETA's favorite town-Fishkill. There's a variation at NY 135's interchange with NY 107. I-81 has one that is like this on the NB side in Cortland.

So is that done on purpose?
The only reason I can see is a "poor man's SPUI" type of operation, where SB I-84 -> east main st and west Main st -> SB I-84 left turns can go at the same time, with off-ramp traffic going into a "storage gap". Not sure if you can have enough capacity to make it work and enough traffic to make it worth it at the same time... "storage gap" looks like 7-8 cars long in this case..

[paulthemapguy]

It took me a while to figure out ((WHAT THE HECK IS HE TALKING ABOUT)) but I think I got it.
Some diamond interchanges will have the exit ramps bow out and then straighten, to form a right angle with the target street, making for a safer intersection.  Then, the entrance ramp is set to begin at the same point along the target street, and since the ramp is one-way leading away from the street, there is no need to check for traffic coming from it, and thus no reason to keep it at a right angle.

I-57 at Manhattan-Monee Road is a good example of this.  The exit ramp meets Manhattan-Monee at a right angle, so that drivers on the ramp can easily look both ways when trying to make a turn--there's no rubbernecking to see if cars are coming due to some wonky angle.  However, since no one is anticipating traffic from the entrance ramp, no one cares if the entrance ramp is built on an angle that approaches the Interstate head-on.  So engineers design the entrance ramps straight to cut costs.  https://www.google.com/maps/@41.4280928,-87.7593251,15.93z

I don't think that this interchange design is exclusive to Illinois, though.  Hope this made sense.

[Aerobird]

A variation on this is in Tallahassee, Florida, where I-10 interchanges with US-319 and FL-61.

Going eastbound, the off-ramp from I-10 comes down to FL-61, but going straight across doesn't become an on-ramp, but rather Raymond Diehl Road, which has several businesses on it and also acts as the eastbound connection to US-319. The on-ramp actually is an intersection on Raymond Diehl, directly across from a hotel entrance-exit.

Westbound, there used to be no direct connection to US-319, with all traffic going onto 61 (which Ys into 319 itself just north of the interchange). A recent reconstruction project recently added connections directly to and from 319.