Innovative Intersections Displaced Left Turn

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 three legs
  • With heavy through traffic volumes on the major street
  • With moderate to low left-turn traffic volumes on the side street
  • Where there are no driveways along the major street opposite the side street
  • With a limited number of pedestrian crossings across the major street or with an alternative pedestrian crossing location nearby

Benefits

• Improved safety: Channelizing left-turn vehicles from the side street reduces the potential for angle crashes
• Increased efficiency: One direction of travel on the major street is free-flow, and, as a result, more green time can be provided to the other movements, reducing delay
• Free-flow in one direction: One direction of travel on the major street never stops, which improves traffic signal synchronization and reduces corridor travel times

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 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.

Resources