Innovative Intersections and Interchanges

 

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Contraflow Left Interchange icon
Innovative Intersection: Contraflow Left
I-35 at East Hopkins Street, San Marcos, Texas

A DLT is also known as:

  • Continuous Flow Interchange

What Is A DLT Interchange?

  • Design where left-turn vehicles cross to the other side of the opposing through traffic in advance of the freeway ramps
  • Protected left turns and opposing through movements occur simultaneously at the two ramp intersections
  • Ramp intersections and crossovers are signalized and timed to work together to minimize stops
  • Can be designed as an overpass or an underpass

When Should It Be Considered?

  • With heavy through traffic volumes in both directions of the arterial roadway
  • With moderate to heavy left-turn traffic volumes onto the freeway ramps
  • With low to moderate left-turn traffic volumes onto the arterial from the freeway
  • With limited bridge width, but with right of way available approaching the bridge

Benefits

  • Improved safety: Spreads out the number of potential conflict points where vehicles may cross paths
  • Increased efficiency: Simultaneous movement of protected left turns and opposing through movements allows for only two traffic signal phases rather than the typical four, which reduces delay
  • Better synchronization: Corridor travel times are improved through elimination of left-turn traffic signal phases and synchronization of the ramp intersections and crossover traffic signals, allowing through traffic to spend less time stopped

How to Navigate

Below shows how to navigate a DLT interchange. Click the image to view a larger version.

DLT Interchange 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 diamond interchange to a DLT interchange.

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 diamond interchange, a DLT interchange has the same number of conflict points.

Conventional Diamond Interchange: Conflict Points

Conventional Intersection 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

DLT Interchange: Conflict Points

DLT 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

Virginia Department of Transportation

Page last modified: Nov. 7, 2019