Summary of "Placemaking Alternative Intersection" research 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.
Before: Typical Stroad, but setbacks are large enough that yellow carve-outs will not impact buildings.
After: U-turns create 3-ph or 2-ph signal. More pedestrian crossings & ped refuge. Chicanes slow traffic.
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Left: Shortly after project opens.
Right: Years later after market has time to react to walkable environment! Many original buildings still there, but many "higher and better" mixed-use buildings have also been built.
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. in Greenville, NC.
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.
