Turn Lane Warrants: Concepts, Standards, Application in … Design Considerations/David... · Turn Lane Warrants: Concepts, Standards, Application in Review David J. DeBaie P.E.,

Turn Lane Warrants:Concepts, Standards,

Application in Review

David J. DeBaie P.E., P.T.O.E.

2004 ITE District 1 Annual MeetingBurlington,Vermont

Turn Lane Warrants Review

Included

• Left and Right• 2 & 4 Lanes• Unsignalized• Hourly Volume

Turn Lane Warrants Review

Not Included

•Accidents•V/C Ratio•Delay•LOS

STANDARDS

Turn Lane Warrants

ASSHTO Guidance

NoneAASHTO(HRR 211)

UnSignalized

ASSHTO(HCM)

ASSHTO(HCM)

SignalRightLeft

States’ Unsignalized Turn LaneGuidance Sources

•Cottrell•Harmelink

Harmelink

•TRR 855•HRR 211

•AASHTO•HRR 211

RightLeft

CONCEPTS

Right Turn Lane Warrants and Guidelines

Right Turn Lane Warrants and Guidelines

• Cottrell, B.H. JR., Guidelines for Treatment of Right-Turn Movements on Rural Roads, in TRR 855, 1982.

• Virginia HTRC, The Development of Criteria For the Treatment of Right Turn Movements on Rural Roads, 1981 (in NCHRP 279, 1985).

• Willey,L.B.,Traffic Volume Warrants for Right Turn Auxiliary Lanes at Unsignalized Intersections, 1989 ( in VTrans Guidelines, 1994)

Cottrell’s and VHTRCRight Turn Lane Guidelines

States’Right Turn Lane Guideline

Vtrans’ Right Turn Lane Warrants

CONCEPTS

Left Turn Lane Warrants and Guidelines

Left Turn Lane Warrants

Harmelink, M.D., Volume Warrants for Left-Turn Storage Lanes at Unsignalized

Grade Intersections, in HRR 211, 1967.

Harmelink Left Turn Lane Warrant

Probability of an advancing through vehicle in a queue behind a left-turn vehicle waiting for gap in opposing flow.

Harmelink Warrant Forms

Harmelink’s Warranting Probabilities

0.0050.0300.01060

0.0050.0300.01550

0.0050.0300.02040

DividedUndivided

4-Lane2-LaneSpeed(mph)

Probability of Thru VehicleArriving in Queue

Harmelink's Model-Queue Theory Utilization:

Arrival RateService Rate

Harmelink’s Model-Arrival Rate:

[(Percent lefts)(1-Percent lefts)(Advancing Volume)]

X[(average Time to Wait) + (Time to Clear adv.lane)]

[0.667 (mean Headway of Adv.Volume)]

Harmelink’s Model-Service Rate:

Unblocked Time in Opposing FlowTime to Turn Left

Harmelink Model-Time Assumptions (seconds)

NA1.9Clear Adv. Lane

4.0 3.0 Left Turn

6.05.0 Critical Gap

4-Lane2-Lane

Left Turn Warrant Application

NNNN40200200?Y?N20400400?Y?N15400600YYYOff15800800YOffOffOff 1010001000

60 mph50 mph40 mphLeftTurnAdvancingOpposing

NCHRP 279 Graph

Four-Lane

AASHTO Table

Two-LaneVolumes

Harmelink Concept Applied

• AASHTO “ Green Book”• NCHRP 279 “ Intersection Channelization

Design Guide”• NCHRP Synthesis 225 “ Left Turn

Treatments at Intersections”• NCHRP 348 “ Access Management

Guidelines for Activity Centers”

NCHRP 279 Consistency

NCHRP 348 Figure 9-14 (Four-Lanes Only )

NCHRP 225

DHV>100/lane12 lefts Warrant

GraphIdaho Transportation Department

Altered Axes Expanded Graphs 2 and 4 Lanes

ITE 4A-22(Harmelink)

2-Lane TableASSHTO(Harmelink)

Unsignalized Left Turn

ApplicationConceptSourceWarrant

Type

Harmelink’s WarrantConditions Expanded

1990 ITE Committee 4A-22 “ Guidelines for Left- Turn Lanes”

Harmelink overestimate suggested.

Harmelink’s Warrant’s Accuracy Evaluated

Kikukchi and Chakroborty, Analysis of Left-Turn Lane Warrants at Unsignalized T-Intersections on Two –Lane Roadways, in TRR 1327, 1991

• Two problems with Harmelink were noted .• Harmelink underestimate suggested.

Kikuchi and ChakrobortyProblems with Harmelink

• Inconsistent definitions for arrival and service rates.

• Incorrect left turn possibilities in the service rate.

Kukuchi and Chakroborty Issue with Harmelink Definitions

• Arrival Rate relates to through vehicles arriving in a left turn vehicle queue.

• Service Rate relates to left turning vehicles.

• If one through vehicle-OK. • If multiple throughs in queue then arrival

rate is overstated and warrant is too low.

Kukuchi and Chakroborty Issue with Harmelink Left Turns

• Harmelink left turn capacity calculation:(1) count gaps greater than the required time to turn; (2) these gaps reduced by one half the critical gap;

and time to turn subtracted; gap remainders aggregated; and divided again by the time to turn.

• Overestimated left turn capacity is suggested.