Intersection & Interchange Geometrics (IIG)
Module 5
Innovative Design Considerations for All Users
Displaced Left
Turn (DLT)
Intersections
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
2
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
3
SR 30 and Summit Rd in Fenton, MO
Source: Bing
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
4
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
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
• With channelized right turns
• Without channelized right turns
6
Displaced Left Turn Intersections
Known information as of Sep 1, 2014
Washington
New Hampshire
Montana
North Dakota
Maine
Vermont
Minnesota
Oregon
Massachusetts
Idaho
South Dakota
Wyoming
Michigan
Nebraska
Nevada
California
Utah
New York
Wisconsin
Iowa
Illinois
New Jersey
District of Columbia
Indiana
West Virginia
Virginia
Missouri
Oklahoma
New Mexico
Arkansas
North Carolina
Maryland
South Carolina
Mississippi
Texas
Delaware
Kentucky
Tennessee
Arizona
Connecticut
Ohio
Colorado
Kansas
Rhode Island
Pennsylvania
Alabama
Georgia
Louisiana
Alaska
Florida
Hawaii
Operational
In Construction
Advanced Design
In Study
Puerto Rico
7
PARTIAL DLT – CONFLICT POINTS
32 Conflict Points
30 Conflict Points
8
PEDESTRIAN CROSSINGS
 Potential for 1 Stage Ped Crossings
9
PEDESTRIAN CROSSINGS
Miami Township, OH
Sample Ped Crossings at a DLT
PEDESTRIAN CROSSINGS
Sample
configuration
with direct
pedestrian
crossing paths
and no conflict
with free-flow
right turn lanes
11
CROSSINGS WITH REFUGE ISLANDS
12
BICYCLE OPTIONS
On Street Option
Off Street Option
13
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.
14
POTENTIAL BUS STOP LOCATIONS
15
T YPICAL 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.
DLT
CORRIDOR
B a n g e r te r H w y
S a l t L a ke Va l l ey
Utah
Crash reductions
of 60%
Travel time
reductions
UNBALANCED VOLUMES
Redwood Road & West 6200 South
Taylorsville, UT
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 leftturn demand should have longer spacing.
19
DLT CROSSOVER DESIGN
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.
21
SIDE BY SIDE TURNING PATHS
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
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)
LEFT TURN MANUEVER
SEMI-TRUCK MANEUVERS
RIGHT TURN BYPASS/FRONTAGE ROAD
27
SIGNALIZED RIGHT TURN LANE
30
DLT WITHOUT CHANNELIZED RIGHT TURNS
31
WITHOUT RIGHT TURN BYPASS
ACCESS MANAGEMENT
33
SAMPLE ADVANCE SIGNING FOR DLT
34
POTENTIAL SIGNAL POLE LAYOUT
35
POTENTIAL ANGULAR ARROW DISPLAY
AT CROSSOVERS
36
PAVEMENT MARKINGS
Follow the general pavement marking concepts in the MUTCD
Potential use of “KEEP CLEAR” pavement marking
37
LEARNING CHECK
Module 5 – Displaced Left Turn (DLT)
TRUE or FALSE
The DLT is a very effective intersection safety
measure for rural low volume intersections
38
QUESTIONS