1. Module 5 Displaced Left Turn (DLT) Intersections
Intersection & Interchange Geometrics (IIG)
Innovative Design Considerations for All Users

2. DLT – DISPLACED FEFT TURN
(aka Continuous Flow Intersection)
At-grade intersection form with the left-turn movements on one or more of the approaches relocated to the other side of the opposing traffic flow

3. Displaced Left-Turn (DLT)
Distinguishing Feature:
Left-turn movement (on one or more approaches) strategically relocated to the far-side of the opposing roadway via interconnected signalized crossover in advance of the main intersection
Key Message: Facilitator will introduce the DLT Intersection design as a non-traditional intersection alternative. This diagram shows the path of the left-turn vehicles from the mainline.
Background Information: N/A
Interactivity: Show the video of a DLT Intersection. This will help to illustrate the concept and generate thought.
Notes:
SR 30 and Summit Rd in Fenton, MO
Source: Bing

4. Displaced Left-Turn (DLT) Intersection
Distinguishing Feature:
Relocation of the left-turn lanes to the other side of opposing traffic on one or more approach

5. Suffolk County 46 at the entrance to Dowling College in Shirley, NY
DLT Intersection
Allows left turns and opposing through movement to occur at the same time (eliminate left-turn signal phase)
Suffolk County 46 at the entrance to Dowling College in Shirley, NY

6. Potential Configurations:
Displaced Left-Turn (DLT) Intersection
Potential Configurations:
Three-legged DLT intersection with major street displaced left
Three-legged DLT intersection with minor street displaced left
Four-legged DLT intersection with major street displaced lefts
With channelized right turns
Without channelized right turns
Four-legged DLT intersection with four displaced lefts
Key Message: The DLT Intersection has several “varieties” as listed on the slide. 6

7. Displaced Left Turn Intersections
Known information as of Sep 1, 2014
Alaska
Arkansas
California
Colorado
Connecticut
Delaware
District of Columbia
Hawaii
Idaho
Illinois
Iowa
Kansas
Kentucky
Maine
Maryland
Massachusetts
Michigan
Minnesota
Missouri
Montana
Nebraska
Nevada
New Hampshire
New Jersey
New Mexico
New York
North Carolina
North Dakota
Ohio
Oklahoma
Oregon
Pennsylvania
Puerto Rico
Rhode Island
South Dakota
Texas
Utah
Vermont
Virginia
Washington
West Virginia
Wyoming
Alabama
Arizona
Florida
Georgia
Indiana
Louisiana
Mississippi
South Carolina
Tennessee
Wisconsin
Operational
In Construction
Advanced Design
In Study

8. Partial DLT – Conflict Points
Key Message: The figure on the left shows the conflict points of a partial DLT Intersection with left-turn crossovers on only the mainline approaches. The total number of conflict points in this case is 30 compared to the 32 conflict points at a conventional intersection. A full DLT Intersection has 2 fewer conflict points for a total of 28. While the slightly lower number of conflict points may reduce the probability of a crash, the important point to note is that the conflict points are more spread out at a DLT Intersection compared to the conventional intersection.
Background Information: A possible safety disadvantage is the unfamiliarity of drivers with the design. There are several counterintuitive design features of the DLT Intersection. These features could be expected to result in driver confusion in several ways including the following:
Drivers are familiar with making a left-turn maneuver at the main intersection. In the case of a DLT Intersection, the indirect left-turn occurs several hundred feet ahead of the main intersection. Even with adequate signage, this will require drivers to anticipate the left-turn in advance.
The counterintuitive design features of a DLT Intersection and the absence of turn movements at the main intersection can also lead to wrong-way movements. Wrong-way movements can be reduced by providing adequate signage and pavement markings.
Interactivity: N/A
Notes: 8

9. Pedestrian crossings Potential for 1 Stage Ped Crossings
Key Message: Crosswalks at a median u-turn intersection are at the same places they would be at a comparable conventional intersection. The major street crossing could be made in one or two stages and the median can be used to provide a refuge for 2-stage crossing. If pedestrian signals and push-button controllers are provided, the devices will need to be installed in the median as well.
Background Information: A one-stage crossing, i.e., crossing both directions of the major street during one signal phase, is possible if the distance is not too long and the necessary green time for that phase does not take too much green time away from major street. At many median u-turn intersections in Michigan, these conditions have not been met and a two-stage crossing of the major street is provided. In a two-stage crossing, a pedestrian crosses one direction of the major street during one signal phase and the other direction during a second signal phase, often with some delay between the phases. Because there are only two signal phases and the cycle lengths should be short, the amount of delay to a pedestrian due to the two-stage crossing should be relatively small. If pedestrian signals and push-button controllers are provided, the devices will need to be installed in the median as well as on the sides of the road.
Pedestrians with vision and cognitive impairments should find crossing a median u-turn intersection to be no more challenging than crossing a comparable conventional intersection. The cues pedestrians with vision impairments rely on to cross intersections, such as the sound of traffic parallel to their crossing, will be similar. All pedestrians should benefit from the simpler two-phase signal timing and the lower number of conflicting traffic streams than at a conventional intersection.
Interactivity: N/A
Notes:

10. Pedestrian crossings Sample Ped Crossings at a DLT Miami Township, OH
Key Message: Crosswalks at a median u-turn intersection are at the same places they would be at a comparable conventional intersection. The major street crossing could be made in one or two stages and the median can be used to provide a refuge for 2-stage crossing. If pedestrian signals and push-button controllers are provided, the devices will need to be installed in the median as well.
Background Information: A one-stage crossing, i.e., crossing both directions of the major street during one signal phase, is possible if the distance is not too long and the necessary green time for that phase does not take too much green time away from major street. At many median u-turn intersections in Michigan, these conditions have not been met and a two-stage crossing of the major street is provided. In a two-stage crossing, a pedestrian crosses one direction of the major street during one signal phase and the other direction during a second signal phase, often with some delay between the phases. Because there are only two signal phases and the cycle lengths should be short, the amount of delay to a pedestrian due to the two-stage crossing should be relatively small. If pedestrian signals and push-button controllers are provided, the devices will need to be installed in the median as well as on the sides of the road.
Pedestrians with vision and cognitive impairments should find crossing a median u-turn intersection to be no more challenging than crossing a comparable conventional intersection. The cues pedestrians with vision impairments rely on to cross intersections, such as the sound of traffic parallel to their crossing, will be similar. All pedestrians should benefit from the simpler two-phase signal timing and the lower number of conflicting traffic streams than at a conventional intersection.
Interactivity: N/A
Notes:
Miami Township, OH
Sample Ped Crossings at a DLT

11. Pedestrian crossings
Sample configuration with direct pedestrian crossing paths and no conflict with free-flow right turn lanes

12. Crossings with refuge islands

13. Bicycle options
On Street Option
Off Street Option

14. Bicycle left turns
Consider providing a “bicycle box” in the far-side pedestrian island for bicyclists to complete a left turn through the main intersection.

15. Potential bus stop locations

16. Typical signal coordination
In Step 1, the left-turn crossover upstream of the main intersection gives green to crossover vehicles at the same time the minor street movements occur at the main intersection.
By the time the crossover vehicles reach the main intersection, Step 2 (the next phase) will have begun, allowing the left turns to discharge at the main intersection.

17. DLt corridor Crash reductions of 60% Travel time reductions
Bangerter Hwy
Salt Lake Valley
Utah
Crash reductions of 60%
Travel time reductions

18. Unbalanced volumes
Redwood Road & West 6200 South
Taylorsville, UT

19. Crossover intersection spacing
The distance between the main intersection and the crossovers generally ranges from 300 to 500 feet, but there are trade-offs to be considered.
Short spacing may result in queue spillback and reduce the ability to clear queues through a single signal cycle
Long spacing may be more difficult to coordinate signal operations
Spacing greatly affects signal timing strategies and coordination between movements.
In general, a DLT approach with higher left-turn demand should have longer spacing.

20. Desirable Undesirable DLT crossover design
Key Message: This slide indicates the typical distance between the intersection and median opening.
Indicate that the median opening is typically located 400 – 1000 ft downstream of the minor road.
Also note the distances set forth in AASHTO and those adopted by the MI and NC DOT.
Discuss issues associated with the distance between the intersection and median opening:
Vehicles from the minor road must perform weaving maneuvers to access the median u-turn.
Longer distances are preferred for weaving, but as the distance between the intersection and median opening increases, the delay for the minor road left-turn and through vehicles increases.
Longer distances also decrease the probability of spillback.
Distance will depend on the cross-section (number of lanes), speed limit of the roadway, and traffic volume.
Background Information: AASHTO recommends spacing from 400 to 600 ft for median u-turn designs based on signal timing. The Michigan DOT experience with median u-turns has led it to establish 660-ft (+/- 100-ft) as the standard spacing. The North Carolina DOT standard spacing for Restricted Crossing U-Turn Intersections is a minimum 800 ft.
To accommodate constraints related to drainage, sight distances, or available rights-of-way, crossovers can be shifted toward or away from a main intersection with relatively little adverse effect on traffic operations. Locating a crossover so vehicles can make u-turns or left turns into a driveway or downstream side street is common practice at median u-turns in Michigan.
Interactivity: N/A
Notes:
Undesirable

21. Crossover intersection geometry
The objective is to provide a smooth alignment for the through traffic.
Align the left turns at the stop bar with the receiving lanes (for the displaced left turn pockets) to reflect desirable vehicle path alignment to minimize path overlap.

22. Side by side turning paths

23. Semi-truck maneuvers
Accommodating a WB-67 (67-foot tractor-trailer truck) may require using both lanes (if that is a legal maneuver within the given jurisdiction).

24. Note the tight turning radius for the crossover movement at this DLT in Fenton, MO serving the entrance into a shopping mall (primarily passenger cars)

25. Left turn manuever

26. Semi-truck maneuvers

27. Right turn bypass/frontage road

28. Key Message: This photo shows the left turn lanes displaced to the left of oncoming traffic. Also, note the right-turn bypass lane in the photo.

29. Key Message: This photo shows the upstream left turn crossover intersection. Note the nearly perpendicular angle of crossing to help reduce the risk of wrong-way turns. Ask what design vehicle this might accommodate. Note that since this is the main entrance into a large retail development it is mainly passenger cars and delivery trucks have an alternate rear entrance into the complex.

30. Signalized right turn lane

31. DLT without channelized right turns
Key Message: This slide indicates the typical distance between the intersection and median opening.
Indicate that the median opening is typically located 400 – 1000 ft downstream of the minor road.
Also note the distances set forth in AASHTO and those adopted by the MI and NC DOT.
Discuss issues associated with the distance between the intersection and median opening:
Vehicles from the minor road must perform weaving maneuvers to access the median u-turn.
Longer distances are preferred for weaving, but as the distance between the intersection and median opening increases, the delay for the minor road left-turn and through vehicles increases.
Longer distances also decrease the probability of spillback.
Distance will depend on the cross-section (number of lanes), speed limit of the roadway, and traffic volume.
Background Information: AASHTO recommends spacing from 400 to 600 ft for median u-turn designs based on signal timing. The Michigan DOT experience with median u-turns has led it to establish 660-ft (+/- 100-ft) as the standard spacing. The North Carolina DOT standard spacing for Restricted Crossing U-Turn Intersections is a minimum 800 ft.
To accommodate constraints related to drainage, sight distances, or available rights-of-way, crossovers can be shifted toward or away from a main intersection with relatively little adverse effect on traffic operations. Locating a crossover so vehicles can make u-turns or left turns into a driveway or downstream side street is common practice at median u-turns in Michigan.
Interactivity: N/A
Notes:

32. Without right turn bypass

33. Access management

34. Sample advance Signing for DLt
Key Message: Facilitator will discuss the typical signing and markings associated with the Restricted Crossing U-Turn Intersection:
It is critical to provide sufficient signing, particularly for drivers on the minor road. It may not be intuitive for left-turning or through drivers on the minor road.
More guide signing is required than conventional intersection. Ex. Extra confirmation sign on each approach to confirm U-turn
Of course, there needs to be signing to indicate the prohibition of left-turn and through movements from the minor road.
Lane placement is also critical for minor road drivers; those utilizing the median u-turn should position themselves in the left most lane on the minor road.
Background Information: There is the option to provide median openings for passenger cars only and separate median openings for large vehicles. This would be done to reduce the required median width and direct large vehicles to median openings where they can be accommodated. In this case, it is particularly important to provide adequate signing.
Drivers have adjusted quickly to all three recent Restricted Crossing U-Turn Intersection installations in North Carolina. Very few wrong way movements through crossovers have been observed at rural intersections and very few red light runners were observed at crossovers on U.S. Rt.17, and overall traffic seems to flow smoothly. One concern expressed prior to implementation for all three areas was that these were all areas with high concentrations of tourists and retirees who might be surprised or slower to adapt to new traffic patterns. Those concerns have generally subsided.
Interactivity: N/A
Notes:

35. Potential signal pole layout

36. Potential angular arrow display at crossovers

37. Potential use of “KEEP CLEAR” pavement marking
Pavement markings
Follow the general pavement marking concepts in the MUTCD
Potential use of “KEEP CLEAR” pavement marking

38. Learning check TRUE or FALSE Module 5 – Displaced Left Turn (DLT)
The DLT is a very effective intersection safety measure for rural low volume intersections
Upon completion of the training, participants will be able to:
• Describe key design and operation features of six non-traditional intersections and interchanges
• List the advantages and disadvantages of their use
• Describe where they are best suited for existing and planned conditions
• Identify resources to acquire additional information on these designs and their implementations
Key Message: These non-traditional intersection and interchange designs are meant to extend the engineer’s toolbox. They are not applicable in all situations and this presentation will shed some light on the basic features of the designs as well as the applicability. This course will provide an overview of each concept, including the salient geometric, operational, and safety features associated with each design.

39. Questions