turn lane warrants: concepts, standards, application in … design considerations/david... · turn...
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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
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.