Innovative Intersections and Interchanges
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What Is A Center Turn Overpass?
- An intersection that elevates all left-turn movements from the main intersection using ramps in the median
- Left-turn vehicles use an acceleration lane to merge with through traffic
- Both the elevated and at-grade intersections are controlled by a two-phase signal
- Uses the same operating principals as a conventional intersection
- All pedestrian sidewalks and crosswalks are at grade
When Should It Be Considered?
- Where there is heavy left-turn traffic volume
- Where the major and side streets have similar left-turn traffic volumes
- Where the major street is six lanes or wider
- Where there is limited right of way to expand
Benefits
- Improved safety: Reduces the number of points where vehicles cross paths and decreases the potential for angle crashes. Eliminates points where pedestrians and left-turn vehicles cross paths
- Increased efficiency: Separates left-turn movements from through traffic — allowing fewer traffic signal phases, which reduces delay and increases capacity
- Better synchronization: Synchronization of the two signalized intersections improves corridor travel times on both major and side streets
How to Navigate
Below shows how to navigate a center turn overpass intersection. Click the image to view a larger version.
Conflict Points
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 move in opposite directions.
The diagrams below compare possible vehicle travel movements and associated conflict points at a conventional four-leg intersection to a center turn overpass.
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 center turn overpass has eight fewer crossing conflict points.
Conventional Intersection: Conflict Points
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Center Turn Overpass: Conflict Points
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