Evolution of Design
The only known application of the Windmill Design is located at the intersections of US 35 and OH 32/124 in Chillicothe, OH. No information has been obtained as to why the interchange design was chosen at this location.
Design & Operations
The windmill serves two arterial roadways by grade separation. All turning movements are served by a right-hand exit ramp, with stop sign or traffic signal at the ramp termini.+ Vehicles make right and left-turn movements at the ramp intersections and are removed from the main intersection in conventional intersection design. Left turns can turn into left merge lanes, so vehicles have to wait gaps in arterial traffic in only one direction (similar to the Continuous Green T-intersection operations.) This application is best suited for locations where free-flow through movements are desired for both intersecting roadways, with moderate to low turning movement volumes This interchange design is best suited for rural locations where ROW is available at the intersection quadrants and quadrant development is low to minimize attraction of turning movement volumes.
Studies & Research
In a recent simulation study of several grade-separated intersections, the Single Loop was found to have competitive operations with Diamond and Partial Cloverleaf interchanges at low- to medium left turn volumes. Advantages of the Single Loop include minimized right-of-way requirements compared to the Parclo interchange (requiring significant right-of-way in only one intersection quadrant), adaptability to future arterial or cross street widening, and simpler pedestrian crossings. Disadvantages include greater left turn storage requirements, difficulty in maintaining access (if allowed) to parcels within the loop roadway at higher volume levels and greater potential for motorist confusion as not all turns are natural movements.
No research studies or field-reviews have been conducted at this intersection to date.