Innovative Intersections and Interchanges
What Is A DLT?
- Intersection design where left-turn vehicles cross to the other side of the opposing through-traffic in advance of the main intersection
- Left turns and opposing through movements occur simultaneously at the main intersection
- Intersection can be designed as a partial DLT, with crossovers for left turns only on the major street, or a full DLT, with crossovers for left turns on both the major and side streets
- Main intersection and crossovers are signalized and timed to work together to minimize stops.
When Should It Be Considered?
- At intersections:
- With moderate to heavy traffic volumes in all directions
- Where opposing legs have similar through traffic volumes
- With heavy left-turn traffic volumes
- With a limited number of driveways or access points near the intersection
- Improved safety: Reduces and 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 phases, which reduces delay
- Better synchronization: Elimination of left-turn traffic signal phases and synchronization of the main intersection and crossover traffic signals allows through-traffic to spend less time stopped, which improves corridor travel times
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 the possible vehicle travel movements and associated conflict points at a conventional four-leg intersection to a DLT.
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 partial DLT, with displaced left turns on two of the four intersection approaches, has two fewer crossing conflict points.
A full DLT, with displaced left turns on all four approaches, has four fewer crossing conflict points when compared to a conventional four-leg intersection.
Conventional Intersection: Conflict Points
DLT: Conflict Points (Full)
DLT: Conflict Points (Partial)