Innovative Intersections and Interchanges
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What Is A Bowtie?
- An intersection where left-turn movements are completed at an adjacent roundabout
- There are roundabouts on the side street, before and after the main intersection
- The roundabouts can have two to four legs
- Traffic entering the roundabout slows and yields to traffic already inside
- The roundabouts' diameters vary depending on speed, volume, vehicle size and number of legs
When Should It Be Considered?
- With moderate to heavy through traffic volumes and low to moderate left-turn traffic volumes
- With narrow or nonexistent medians and/or limited right of way to expand
- Improved safety: Reduces the number of points where motorists, pedestrians and bicyclists may cross paths. Promotes lower speeds at the roundabouts, giving drivers more time to react
- Increased efficiency: Since there are no left turns at the main intersection and the adjacent intersections are yield controlled, a bowtie has fewer traffic signal phases, which reduces stops and delay
- Shorter wait times: Fewer traffic signal phases means less time stopped at the main intersection
- Cost effective: Can be more cost effective than adding lanes to increase capacity
How to Navigate
The number of conflict points (locations where vehicle travel paths intersect) is one metric that can be used to evaluate the safety of an innovative intersection or interchange.
There are three categories: crossing, merging or diverging.
In general, merging and diverging conflict points — where vehicles are moving in the same direction — are associated with less severe crash types than crossing conflict points where vehicles are moving in opposite directions.
The diagrams below compare possible vehicle travel movements and associated conflict points at a conventional four-leg intersections to a bowtie.
These diagrams represent a general case, with one travel lane in each direction, and do not take into account pedestrian or bicycle movements at an intersection or interchange.
When compared to a conventional four-leg intersection, a bowtie has 12 fewer crossing conflict points.
Conventional Intersection: Conflict Points
Bowtie: Conflict Points