turn lane warrants: concepts, standards, application in … design considerations/david... · turn...
TRANSCRIPT
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Turn Lane Warrants:Concepts, Standards,
Application in Review
David J. DeBaie P.E., P.T.O.E.
2004 ITE District 1 Annual MeetingBurlington,Vermont
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Turn Lane Warrants Review
Included
• Left and Right• 2 & 4 Lanes• Unsignalized• Hourly Volume
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Turn Lane Warrants Review
Not Included
•Accidents•V/C Ratio•Delay•LOS
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STANDARDS
Turn Lane Warrants
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ASSHTO Guidance
NoneAASHTO(HRR 211)
UnSignalized
ASSHTO(HCM)
ASSHTO(HCM)
SignalRightLeft
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States’ Unsignalized Turn LaneGuidance Sources
•Cottrell•Harmelink
Harmelink
•TRR 855•HRR 211
•AASHTO•HRR 211
RightLeft
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CONCEPTS
Right Turn Lane Warrants and Guidelines
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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)
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Cottrell’s and VHTRCRight Turn Lane Guidelines
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States’Right Turn Lane Guideline
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Vtrans’ Right Turn Lane Warrants
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CONCEPTS
Left Turn Lane Warrants and Guidelines
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Left Turn Lane Warrants
Harmelink, M.D., Volume Warrants for Left-Turn Storage Lanes at Unsignalized
Grade Intersections, in HRR 211, 1967.
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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.
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Harmelink Warrant Forms
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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
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Harmelink's Model-Queue Theory Utilization:
Arrival RateService Rate
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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)]
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Harmelink’s Model-Service Rate:
Unblocked Time in Opposing FlowTime to Turn Left
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Harmelink Model-Time Assumptions (seconds)
NA1.9Clear Adv. Lane
4.0 3.0 Left Turn
6.05.0 Critical Gap
4-Lane2-Lane
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Left Turn Warrant Application
NNNN40200200?Y?N20400400?Y?N15400600YYYOff15800800YOffOffOff 1010001000
60 mph50 mph40 mphLeftTurnAdvancingOpposing
NCHRP 279 Graph
Four-Lane
AASHTO Table
Two-LaneVolumes
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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”
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NCHRP 279 Consistency
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NCHRP 348 Figure 9-14 (Four-Lanes Only )
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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
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Harmelink’s WarrantConditions Expanded
1990 ITE Committee 4A-22 “ Guidelines for Left- Turn Lanes”
Harmelink overestimate suggested.
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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.
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Kikuchi and ChakrobortyProblems with Harmelink
• Inconsistent definitions for arrival and service rates.
• Incorrect left turn possibilities in the service rate.
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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.
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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.