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.
Lefts diverted to Quadrants and to "Thru+U+Righ". Traffic-calming U-turns, planted medians, street trees, and bike-ped features help catalyze walkable mixed-uses.
U-Turns just before intersection have traffic-calming safety benefits. They remove many vehicles from signal which reduces delay. Five mountable islands in middle discourage lefts (but allow emergency vehicles). Red lines show new ROW impacts only small amounts of parking.
U-Turns make it easy to install planted medians for safety and access control without creating circulation difficulty. This can/should be done regardless of whether U-turns are used to reduce signal phases from 4 to 3 or 2.
Closeup shows how the auto-oriented environment transitions to pedestrian-oriented. This occurs in large part because the U-turn system reduces delay (increases capacity), in a way that is compatible with walkable uses. (FYI, new vehicle capacity is necessary to support new growth).
Same as before, but compares a no-parking option to a parking option. The no-parking option has bollards and plants as a buffer with traffic, rather than parked cars as the buffer.
Corridor view of how U-turns facilitate transition from auto-oriented to walkable.
Same, but compares bike lane with parking buffer to bike lane with bollard+plants buffer.
Mid-block pedestrian crossing.
Corridors that must accommodate large trucks can still be pedestrian-oriented. In this model, every-other U-turn accommodates large trucks. Many suburban corridors have such large setbacks that fitting U-turns has minimal impacts.
Shows how U-turns at main intersection, for cars only (no big trucks), creates traffic calming and facilitates transition to walkability.
Road diets are normally 4 to 3-lanes (where middle lane is needed for left turning vehicles). With U-turns, center medians are not needed (lefts converted to U+right). Thus, road diets can now be 5 to 4, or 4 to 2, or even 3 to 2!
Create real streets through parking lots, for added connectivity and for more efficient land use.
Still-shots with key messages from some of the previous before/after scenes.
