Most mainline switches (exiting off itself) for a numbered freeway route?

[Duke87]

Interstate 95 is the one route I think does this quite a bit:
{...}
- not sure if I-395 in Groton, Connecticut counts (as I-95 continues southbound along left side)

Nah, the lane configuration isn't right for that to count. Both lanes of 95 NB continue as 95 NB, 395 is a left exit.
Although, 95 does "exit" the Connecticut Turnpike here.

I-278 (you knew it had to come up...) has what is perhaps the most infamous instance of this at the Grand Central Parkway. Not only does all traffic westbound have to get into the right lane and take an exit to stay on 278, the roadway continuing straight ahead is a parkway - so if a truck fails to get over, it's in for some trouble. 
As defined by the OP, 278 has two other definite instances of this: EB at I-478 and WB at I-95/NJTP. There are a couple other instances which may not count but are nonetheless multilane left exits: EB at I-87, and WB at the Belt Parkway split.

The Hutchinson River parkway has an instance of this southbound at exit 15, with three lanes continuing forward as the Cross County Parkway and two exiting to the right to stay on the Hutch... although, in this case it's justifiable: more traffic "exits" at the Cross County than continues through on the Hutch.

[TheStranger]

I-294 in Markham, Illinois (from the 80/294 concurrency going west, 80 exits on the right and enters the multiplex on the right as well)

I-80 exits here, not I-294.  I-294 (Tri-State Tollway) is the mainline.  Currently, it functions more as a split than an exit.

I-90 in Lake Station, Indiana

No, I-80 does the exiting here, not I-90.

That's what I meant for both examples, 80 exiting there.

[huskeroadgeek]

Isn't this called a "TOTSO" (Turn Off To Stay On)?

Technically yes, although I think it's more of a European term.

[froggie]

Isn't this called a "TOTSO" (Turn Off To Stay On)?

Yes and no.  True exit ramps would definitely be considered TOTSOs.  But Mr. Sampang in his original post listed criteria that would also include major route splits and major route merges, which technically aren't TOTSOs.

[xcellntbuy]

Quote
Interstate 95 in metropolitan Washington, DC, both in Maryland and Virginia on the National Capital Beltway

Not anymore in Virginia.  Maryland is arguable, as southbound is designed as a through-route continuation, while northbound you have a "major split" where it breaks off the Outer Loop and a "major merge" where the ramp from the Inner Loop merges.

Thank you for the correction.  The only time I had been through that area was August 1997, late at night and another 300+ miles to try and get home.  No doubt, things have long since changed.

[Hot Rod Hootenanny]

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Some more national examples:

I-70:
I-71 in Columbus

No on I-71.  I-70 is the through route there and I-71 exits itself onto (and off of) I-70

[TheStranger]

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Some more national examples:

I-70:
I-71 in Columbus

No on I-71.  I-70 is the through route there and I-71 exits itself onto (and off of) I-70

The east 70-71 junction in Google Maps has 70 eastbound exiting on the right side from 71 northbound, and 70 westbound entering on the right side onto 71 southbound.  Has this been reconfigured?

[Hot Rod Hootenanny]

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Some more national examples:

I-70:
I-71 in Columbus

No on I-71.  I-70 is the through route there and I-71 exits itself onto (and off of) I-70

The east 70-71 junction in Google Maps has 70 eastbound exiting on the right side from 71 northbound, and 70 westbound entering on the right side onto 71 southbound.  Has this been reconfigured?

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Some more national examples:

I-70:
I-71 in Columbus

No on I-71.  I-70 is the through route there and I-71 exits itself onto (and off of) I-70

The east 70-71 junction in Google Maps has 70 eastbound exiting on the right side from 71 northbound, and 70 westbound entering on the right side onto 71 southbound.  Has this been reconfigured?

Not yet.  Though I see your point.  In that case I-71 exits itself for I-670 as well (last parts of the original Columbus innerbelt interchanges still standing)

[english si]

Isn't this called a "TOTSO" (Turn Off To Stay On)?

Technically yes, although I think it's more of a European term.

Technically it has no name, but British (and Irish copying them) roadgeeks use the term. I would say it is a British term, rather than a European term, as Europe isn't just the islands off the mainland that speak English.

Yes and no.  True exit ramps would definitely be considered TOTSOs.  But Mr. Sampang in his original post listed criteria that would also include major route splits and major route merges, which technically aren't TOTSOs.

British roadgeeks would count any split where you have to go off to the left as a TOTSO, with the exception of the very few right exits - even if there's a 2-2 lane split. Mainlines are considered to be the carriageways separated by a median and nothing else. Therefore the M25 TOTSOs both ways at junction 5, despite it being an even split with three lanes having the middle lane split in two and two lanes to both the M25 and the A21/M26.

The M42 holds the UK motorway record - it has 3 (one at junction 3a and two at the multiplex with the M6 Toll - though they are only in one direction each, due to being forks). The M25 has one, at the aforementioned junction 5. The M1 has one, at junction 42. The M6 has two (forks, so mono-directional) at either end of the M6 Toll, although you could argue the case for one at junction 45, at the end of the motorway. The M60 has one (involving going via a roundabout in one direction - yuck) at junction 18 and the M62, while not signed in multiplex with the M60 has one at junction 12.

[74/171FAN]

I'm surprised no one has mentioned I-83 exiting off itself tiwce within 5 miles of each other in Harrisburg, PA at PA 581 and US 322/I-283

[NJRoadfan]

I-40 now does this west of Greensboro, NC. Originally it was planned to use the Urban Loop (now designated I-73 and I-85) around the city so the interchange was built with that in mind for the main flow of traffic. Then NCDOT instead of making it a 3di, found out that old I-40 through Greensboro would no longer get federal funding... so they routed it back and now I-40 "exits itself" west of Greensboro.

[jdb1234]

Since 1989, US 280 exits off itself at its interchange with the Red Mountain Expressway just south of Birmingham.

[yakra]

- formerly at I-495 in Portland, MA

*AHEM!*

[JustDrive]

I-70 also has the I-29/35 split in Kansas City and the I-670 junction.

[KEVIN_224]

Interstate 95 is the one route I think does this quite a bit:

- not sure if I-395 in Groton, Connecticut counts (as I-95 continues southbound along left side)

The I-95/I-395 junction is to the west in Waterford, CT, as I-395 itself never touches Groton. To this day, it's only a half intersection: I-95 North to I-395 North and I-395 South to I-95 South. That's also the route of the original Connecticut Turnpike from when it was tolled. There's been talk about this interchange being even more complex, when and if CT Route 11 finally gets extended past Connecticut Route 85 in Salem (as it would end at this interchange).

[hobsini2]

I am surprised no one has mention the few instances in Wisconsin.

I-39: Northbound exits right from I-90/94 and Southbound exits right from Wis 78 (Cascade interchange)
I-43: Southbound exits left from I-894 (Hale interchange)
I-43: Southbound exits right from I-94/US41 (Mitchell interchange)
I-90: Westbound exits left from I-94 at Tomah.
I-94: Westbound exits right from I-43 and Eastbound exits right from I-794. (Marquette interchange)
I-94: Westbound exits right from Wis 30 and Eastbound exits left from I-39/90 (Badger interchange)

Also in Illinois, I-39 does a couple times in Rockford. I-39 Southbound exits right from I-90 and exits left from US 20.
I-39 Northbound exits right at US 20.

[WNYroadgeek]

I-86 at I-390 in Avoca, though due to the design of the interchange, this is only the case westbound.

[Urban Prairie Schooner]

I-10 in Baton Rouge exits itself as the mainline becomes I-12, at the New Orleans line it exits itself as the mainline becomes I-610, 3 miles later it exits itself again as the mainline becomes U.S. 90 Business, once in Slidell it exits itself one more time at the interchange with I-59.

Best example is I-10 WB at I-110 in BR - though this is technically a 'correct' exit setup because 110 exits to the 'right', in practice the 10 WB to 110 NB direction serves as the mainline while 10 WB navigates a sharp 35 MPH curve to the left. Three lanes are allocated for 110 NB and two for 10 WB (one lane is shared).

[roadman65]

I-55 in Memphis at the Crump Boulevard Interchange
I-215 near Riverside California
I-280 in Newark, NJ at First Street
I-95 SB Local lanes in Fort Lee, NJ where from the Upper Level GWB, the through lanes become NJ 4 while a single lane slip ramp  exiting from the left carries I-95 SB to merge into the Lower Level Local Lanes.

[national highway 1]

I-5 CA exits off itself at US 101 at the East LA interchange, then at the CA 99 split in Wheeler Ridge, and also at the I-580 split near Tracy.

[Takumi]

US 501 in Lynchburg is mostly an expressway, but it does exit itself 3 times.

[flowmotion]

I-5 CA exits off itself at US 101 at the East LA interchange, then at the CA 99 split in Wheeler Ridge, and also at the I-580 split near Tracy.

(Does anyone else suspect many of these "list all places where..." threads are "write only"?  )

I don't know if I'd categorize Jct I-580 as an "TOTSO" - more like a lane split or left-exit.

[Bickendan]

I noticed quite a few of these on E70 while following directions from Cape Town to Bangkok on Google Earth.

[TheStranger]

I-5 CA exits off itself at US 101 at the East LA interchange, then at the CA 99 split in Wheeler Ridge, and also at the I-580 split near Tracy.

(Does anyone else suspect many of these "list all places where..." threads are "write only"?  )

I don't know if I'd categorize Jct I-580 as an "TOTSO" - more like a lane split or left-exit.

I actually noted 5/580 in the very first post of the thread - it's an interesting case because it wasn't planned as a mainline switch at all, but a split of a suffixed branch (the pre-1964 I-5W)!  Only by circumstance did it become I-5 exiting off itself.

[JustDrive]

The rightmost lane at the 5/580 split is actually formed from the rest area entrance, and then another right lane forms shortly after.  I'd say I-5 exits off itself.