Recently Built Cloverleaf Interchanges

[MillTheRoadgeek]

If you're willing to fudge "20 years" a little bit, I know there's one cloverleaf on the Dulles Greenway (opened 1995, IIRC) at its interchange with Old Ox Road (secondary Route 606). There are no C/D roads there.

I don't know when the cloverleaf at Claiborne Parkway and VA-7 in Loudoun County was built. It certainly wasn't there when I was a kid.

There's a relatively new one on VA-28 at Air and Space Museum Parkway; the museum opened in late 2003 and the interchange was built a little while before that. VA-28 has C/D roads at that one.

https://www.broadlandshoa.org/hoaforum/index.php?threads/full-claiborne-interchange-opens-wednesday.2980/ Open April 2006. The Old Ox/Greenway interchange, believe it or not is also one of the most recent additions - three loop ramps were added on to the original parclo when the Greenway was widened circa 2006-08.
The Air & Space interchange was a parclo upon opening in 2003, to be expanded by 2005. Old Ox/28 opened around 2004-05, Westfields was fall 2005.
And also, a brand new addition - the U.S. 64 bypass's interchange with I-73/74 in Asheboro, NC, opened December 2020.

[StogieGuy7]

I don't even think California has had a new cloverleaf interchange since the 1970s, maybe I-5 at Florin Road in Sacramento or I-5 at Route 132 near Vernalis early in that decade is the most "recent" but most freeway-to-surface road cloverleaf junctions have been converted to parclos since. 

How in the world is a parclo interchange thought to be better and more efficient than a cloverleaf? Yes, cloverleafs have their limitations and have fallen out of favor but a parclo is a stripped down version of a cloverleaf.  Takes up a bit less real estate, but makes up for it with traffic that backs up the exit ramp as cars wait to turn left.

[triplemultiplex]

I don't even think California has had a new cloverleaf interchange since the 1970s, maybe I-5 at Florin Road in Sacramento or I-5 at Route 132 near Vernalis early in that decade is the most "recent" but most freeway-to-surface road cloverleaf junctions have been converted to parclos since. 

How in the world is a parclo interchange thought to be better and more efficient than a cloverleaf? Yes, cloverleafs have their limitations and have fallen out of favor but a parclo is a stripped down version of a cloverleaf.  Takes up a bit less real estate, but makes up for it with traffic that backs up the exit ramp as cars wait to turn left.

Weaving traffic entering and exiting the freeway between loop ramps can screw things up for thru traffic on the freeway if there are no c/d carriageways.

[StogieGuy7]

I don't even think California has had a new cloverleaf interchange since the 1970s, maybe I-5 at Florin Road in Sacramento or I-5 at Route 132 near Vernalis early in that decade is the most "recent" but most freeway-to-surface road cloverleaf junctions have been converted to parclos since. 

How in the world is a parclo interchange thought to be better and more efficient than a cloverleaf? Yes, cloverleafs have their limitations and have fallen out of favor but a parclo is a stripped down version of a cloverleaf.  Takes up a bit less real estate, but makes up for it with traffic that backs up the exit ramp as cars wait to turn left.

I guess I can see that, but it would seem to me that you mitigate one potential problem by creating several others via congestion caused by a less efficient design.

Weaving traffic entering and exiting the freeway between loop ramps can screw things up for thru traffic on the freeway if there are no c/d carriageways.

[Bitmapped]

In Maryland, I-68 Exit #14 (US 40 West/US 219 South) was upgraded to a complete cloverleaf sometime between 1995 and 2004. Looking at historicaerials.com, it appears it was graded as a full cloverleaf from the start but it was paved as a 6-ramp parclo in 1982 when there was a single exit from I-68 in each direction. A direct WB to SB ramp was built by 1993 and the final EB to NB ramp was built by 2004.

Honestly, I'm not sure why this was upgraded to a full cloverleaf. Traffic isn't that heavy and with the snow this area sees, it seems like having fewer ramps to maintain would be better.

[sprjus4]

Forgot to mention before, in the early 2000s, the I-85 / US-58 interchange in South Hill, VA was reconstructed from a folded diamond to a full cloverleaf interchange. Haven't really experienced any problems here, though I'm sure it has caused the occasional issue with the I-85 mainline moving at 70+ mph.

Now a corridor study completed for US-58 recently is recommend conversion to a diverging diamond or a dogbone interchange.

[jakeroot]

I don't even think California has had a new cloverleaf interchange since the 1970s, maybe I-5 at Florin Road in Sacramento or I-5 at Route 132 near Vernalis early in that decade is the most "recent" but most freeway-to-surface road cloverleaf junctions have been converted to parclos since. 

How in the world is a parclo interchange thought to be better and more efficient than a cloverleaf? Yes, cloverleafs have their limitations and have fallen out of favor but a parclo is a stripped down version of a cloverleaf.  Takes up a bit less real estate, but makes up for it with traffic that backs up the exit ramp as cars wait to turn left.

Weaving traffic entering and exiting the freeway between loop ramps can screw things up for thru traffic on the freeway if there are no c/d carriageways.

I guess I can see that, but it would seem to me that you mitigate one potential problem by creating several others via congestion caused by a less efficient design.

Free-flow does not mean higher capacity: the weaving can cause severe congestion and create dangerous speed differential problems. Partial-cloverleaf interchanges do not have these problems by comparison. Signals, stop signs, and yields can seemingly inhibit flow; this is a fallacy.

Partial-cloverleaf interchanges also have designs where the exit has the loop, and the on-ramp uses left turns (coined B4) (example here). Though most have the loop for entering traffic, this is not universal. These 'B4' partial-cloverleafs often do not require any signalization, have no 'intentional' weaving, and don't inherently possess speed differential issues. They have exceptionally high capacity, and the lack of a weave design reduces the chance of them getting bogged down.