Summary of "Placemaking Alternative Intersection" research underway for the North Carolina Department of Transportation.
What is a U-Turn Intersection?
There is a huge amount of variation in the U-Turn family of designs, but the basic idea is to convert lefts into “Thru + U + Right.” In the "Before" diagram, the purple cars require a left-turn arrow – a four-phase signal that creates congestion and requires extra lanes for storing left-turning cars. In the "After," lefts are now “Thru+U+Right.” Before, the blue and yellow cars are also in a predicament. Yellow needs a safe gap in BOTH directions (very hard to get), before it can enter. Blue needs a safe gap in only one direction, but this is still dangerous. The roundabouts make this easier, faster, and safer. Notice that like the Quadrant, the old left turn lanes can now be planted with trees, and you can have pedestrian refuge areas in the crosswalk.
Concepts in Greenville: U-Turns at Red Banks Road
The series of sliders below show Before / After for the U-Turn / two-quadrant intersection at Greenville Blvd and Red Banks Road.
Concepts in Greenville: U-Turn / Quad Combo
Below is a combination U-Turn+Quadrant. This would offer pedestrian refuge that the current design does not. This would make it a lot easier to reduce lane widths and create the ambiance that is necessary for mixed-use areas to take root. The chicanes introduced by what we call "teardrops" (non-roundabout U-turns), have a natural traffic calming effect.
Can this funky stuff fit in with New Urbanism? We think so, but we worry that too many Urbanists may see things through a "Back to the Future" lens - going back to Pre-WWII grids as our model for what is best going forward. That may be fine in Greenfield areas, but isn't helpful in suburbs without grids! This may be a way to fix what is broken - the "future" part of "Back to the Future," where we take crappy Stroads, tweak them with some weird stuff like this, then watch as they grow impressive walkable development that could never have happened without the weird stuff.
I think of these U-turns and Quadrants a little like a stent in an artery. If we compare suburbs to the obesity epidemic, suburbs never should have "eaten" (developed) in a way that ruins their health. Now that they're in a terrible place and facing heart attacks, these ideas may be like stents and stomach stapling, followed up with healthier living. Not as good as healthy living from the beginning, but a new lease on life - a way to get from bad to better.
Below are graphics from our Greenville, NC work, which are part of what we'll try to advance through this NSF grant.
Engineers install "raised medians" to force right-in / right-out, for safety, but this makes it hard to get back to where you came from. Frequent U-turns make it safe and easy, which in turn makes it easy to reclaim two-way turn lanes, or "suicide lanes," for street trees and more walkable uses.