Evaluation of the Safety Effect of Signs and Lane Markings at a

Multilane Roundabout

John Hourdos Minnesota Traffic Observatory

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The Problem with Multilane Roundabouts

• FHWA 2012 Guidance Memorandum • Two-way stop control -> Roundabout,

• 82 percent reduction in severe (injury/fatal) crashes and a 44 percent reduction in overall crashes.

• Signalized intersection -> Roundabout, • 78 percent reduction in severe (injury/fatal) crashes and a 48 percent

reduction in overall crashes.

• Statistics not true for all roundabout designs • TRB Roundabout committee identified 2x2 roundabouts as a

problem • “The Multi-lane Roundabout PDO Dilemma”

• Presentation by FHWA at the 4th International Conference on Roundabouts. http://teachamerica.com/RAB14/RAB14_TAC.htm

• Two Examples focusing on 2x2 roundabouts

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http://teachamerica.com/RAB14/RAB14_TAC.htm

• Bailey/Radio roundabout in Woodbury, MN • 2003-2006, 4-way stop, 2 reported crashes • 2008-2012, 2x2 RB, 132 reported crashes • 2013 converted to 1x2, 4 in the first 6 months

• Washington Co converted all 2x2 RBs to 1x2 • Not a sustainable solution

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• Portland/66th St roundabout in Richfield, MN • Till 2008, Signalized, Third worst in Hennepin County,

(crash severity and cost) • 2008-2011, 2x2 RB, 90 reported crashes • Traffic demand does not allow any lane reductions.

Other solutions were investigated. • Combined AADT around 30,000 vehicles

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Roundabout Signs and Lane Marking Changes • Pavement Markings

• Turn arrows on the approaches to the roundabout and inside the roundabout were changed from “fish-hook” style to the standard

• Additional turn arrows and lane designation signs have been placed at approximately 450 feet upstream of the yield line on all legs of the roundabout.

• Lane Markings • The solid lane line was extended from the original 50 feet upstream of the yield

line to a current 250 feet. • Eliminate solids then skips in circulatory roadway and change to consistent line

gap sequence of 6’ line segment and a 3’ gap 8”wide.

• Signing • Lowering to improve Line-of-sight visibility for one-way signs, median signs, and

large street . “Roundabout Ahead” warning signs were moved to 500 feet from the roundabout.

• Turn arrows on lane designation signs were also changed from “fish-hook” style to the standard style.

• To address the high occurrence of drivers failing to yield to pedestrians, traditional crosswalk signs (W11-2) were replaced with R6-1 paddle signs.

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Implemented Changes on the Roundabout

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Implemented Changes on the Roundabout

Courtesy of MTJ Engineering

Crash History

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Violation Categorizations

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Yield Violations

Turn Violations

Lane Change Violations

Video Collection

Video collection equipment setup

Screenshot of roundabout video

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Video Data Reduction

• Time of entry • Vehicle type • Entrance lane • Type of violation • Correctness of entrance lane

choice • Traffic volumes

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Results: Three periods of Observation

Count Normalized Occurrence Count Normalized Occurrence Count Normalized Occurrence

Before - 2010 (72 hours) After - 2011 (72 hours) One Year After -2012 (72 hours) Traffic Volume 98015 125078 126044 Total Violations 5205 5.31% 4918 3.93% 5607 4.45% Yielding 1021 1.04% 1065 0.85% 1713 1.36% Inner 666 0.68% 771 0.62% 1140 0.90% Outer 300 0.31% 218 0.17% 457 0.36% Both 55 0.06% 76 0.06% 116 0.09% Lane Change 3037 3.10% 3095 2.47% 3073 2.44% Entrance 1301 1.33% 1407 1.12% 1325 1.05% Exit 1736 1.77% 1688 1.35% 1748 1.39% Turn Violation 1135 1.16% 750 0.60% 818 0.65% Right from inner 71 0.07% 77 0.06% 75 0.06% Left from outer 1027 1.05% 665 0.53% 719 0.57% More than 270 from outer 37 0.04% 8 0.01% 24 0.02% Wrong Way 12 0.01% 8 0.01% 3 0.00% Enter 10 0.01% 8 0.01% 3 0.00% Exit 2 0.00% 0 0.00% 0 0.00% Incorrect Lane Choice 1920 1.96% 1152 0.92% 1243 0.99%

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Before - After After - One Year After Before - One Year After Percent

Change p-value Z-statistic Percent Change p-value Z-statistic

Percent Change p-value Z-statistic

Total Violations -26.0%

Violation by Time of Day

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Conclusions

• The changes in the signs and lane markings of the roundabout had an effect.

• Yield violations did not show any improvement. • Lane change violation showed moderate improvement.

• Approximately 20% reduction • Can be attributed to lane marking changes inside the roundabout

• Turn violation showed large improvement • Most severe kind (Left from outer) reduced by 45% • Considering that the “Incorrect Lane Choice” instances also reduced by 50%

the improvement can be mainly attributed to the changes in the roundabout entrances.

• Solid line extension from 50 feet to 250 feet • Additional lane designation signs

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Future Research

• Study results encouraging • One case study is not enough to change MUTCD guidelines • Changes were implemented all together. Difficult to know which

were most effective.

• New study will collect observations on three roundabouts in Minnesota.

• Changes will be implemented incrementally.

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Acknowledgments

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Questions?

John Hourdos, PhD Civil Engineering Dept University of Minnesota T 612-626-5492 F 612-626-7750 E hourdos@umn.edu http://lnkd.in/Hg9abU www.mto.umn.edu

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mailto:hourdos@umn.eduhttp://lnkd.in/Hg9abU

Evaluation of the Safety Effect of Signs and Lane Markings at a Multilane RoundaboutThe Problem with Multilane RoundaboutsSlide Number 3Slide Number 4Roundabout Signs and Lane Marking ChangesImplemented Changes on the Roundabout Slide Number 7Crash HistoryViolation CategorizationsSlide Number 10Video Data Reduction Results: Three periods of ObservationResults: Comparisons Violation by Time of DayConclusionsFuture ResearchAcknowledgments Questions?