Module 5 Displaced Left Turn (DLT) Intersections Intersection & Interchange Geometrics (IIG)...

Module 5

Displaced Left Turn (DLT) Intersections

Intersection & Interchange Geometrics (IIG)Innovative Design Considerations for All Users

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

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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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

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

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.

Bangerter HwySalt Lake Val leyUtah

DLT CORRIDOR

Crash reductions of 60%Travel time reductions

Redwood Road & West 6200 SouthTaylorsville, UT

UNBALANCED VOLUMES

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

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

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

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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

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

QUESTIONS