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Module 5
Displaced Left Turn (DLT) Intersections
Intersection & Interchange Geometrics (IIG)Innovative Design Considerations for All Users
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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
DLT – DISPLACED FEFT TURN
(aka Continuous
Flow Intersection)
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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
SR 30 and Summit Rd in Fenton, MO Source: Bing
DISPLACED LEFT-TURN (DLT)
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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
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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
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POTENTIAL CONFIGURATIONS:
Displaced Left-Turn (DLT) Intersection
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• With channelized right turns• Without channelized right turns
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Alaska
Arkansas
California Colorado
Connecticut
Delaware
District of Columbia
Hawaii
Idaho
Illinois
Iowa
KansasKentucky
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
Known information as of Sep 1, 2014
OperationalIn ConstructionAdvanced DesignIn Study
Displaced Left Turn Intersections
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PARTIAL DLT – CONFLICT POINTS
30 Conflict Points
32 Conflict Points
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PEDESTRIAN CROSSINGS
Potential for 1 Stage Ped Crossings
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Sample Ped Crossings at a DLT
PEDESTRIAN CROSSINGS
Miami Township, OH
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Sample configuration with direct pedestrian crossing paths and no conflict with free-flow right turn lanes
PEDESTRIAN CROSSINGS
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CROSSINGS WITH REFUGE ISLANDS
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BICYCLE OPTIONS
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On Street Option
Off Street Option
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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.
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POTENTIAL BUS STOP LOCATIONS
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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.
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Bangerter HwySalt Lake Val leyUtah
DLT CORRIDOR
Crash reductions of 60%Travel time reductions
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Redwood Road & West 6200 SouthTaylorsville, UT
UNBALANCED VOLUMES
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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.
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DLT CROSSOVER DESIGN
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Desirable
Undesirable
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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.
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SIDE BY SIDE TURNING PATHS
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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). 23
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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)
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LEFT TURN MANUEVER
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SEMI-TRUCK MANEUVERS
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RIGHT TURN BYPASS/FRONTAGE ROAD
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SIGNALIZED RIGHT TURN LANE
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DLT WITHOUT CHANNELIZED RIGHT TURNS
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WITHOUT RIGHT TURN BYPASS
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ACCESS MANAGEMENT
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SAMPLE ADVANCE SIGNING FOR DLT
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POTENTIAL SIGNAL POLE LAYOUT
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POTENTIAL ANGULAR ARROW DISPLAY AT CROSSOVERS
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PAVEMENT MARKINGS
Follow the general pavement marking concepts in the MUTCDPotential use of “KEEP CLEAR” pavement
marking
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LEARNING CHECK
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Module 5 – Displaced Left Turn (DLT)
TRUE or FALSE
The DLT is a very effective intersection safety measure for rural low volume intersections
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QUESTIONS