Innovative Intersections and Interchanges

 

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Innovative Intersection: Single Loop Intersection
Chippenham Parkway/Parham Road at River Road, Henrico, Va.

What Is A Single Loop?

  • An intersection where all four left-turn movements and some, or all, right-turn movements are rerouted onto a connector road
  • Major and side streets are grade separated
  • Single loops are typically signalized, but not necessarily
  • A staircase or ramp may be used to shorten pedestrian paths between the elevated and at-grade roadways

When Should It Be Considered?

  • At intersections with low to medium left-turn traffic volumes
  • To connect a high-speed street with heavy traffic volumes to a slower, less-traveled street
  • To connect existing grade-separated streets

Benefits

  • Improved safety: Reduces and spreads out the number of points where vehicles, pedestrians and bicyclists may cross paths
  • Increased efficiency: Rerouting left turns allows for fewer traffic signal phases, which means less time waiting for through and right-turn vehicles
  • Better synchronization: Synchronization of the two signalized intersections improves corridor travel times on both the major and side streets

How to Navigate

Below shows how to navigate a single loop intersection. Click the image to view a larger version.

Single Loop navigation diagram

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 are moving in opposite directions.

The diagrams below compare possible vehicle travel movements and associated conflict points at a conventional four-leg intersection to a single loop.

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 single loop has 10 fewer crossing conflict points.

Conventional Intersection: Conflict Points

Conventional Intersection conflict diagram.

Legend

Diagram Legend. Filled circle is diverging, half-filled is merging, empty is crossing.
Conflict Type Count
Crossing 16
Merging 8
Diverging 8
Total:

32 Conflicts

Single Loop: Conflict Points

Single Loop conflict diagram.

Legend

Diagram Legend. Filled circle is diverging, half-filled is merging, empty is crossing.
Conflict Type Count
Crossing 6
Merging 8
Diverging 8
Total:

22 Conflicts

Resources

Page last modified: Nov. 7, 2019