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Alternative Intersection Design and Selection (2020)

Chapter: Appendix H - Summary of Safety Evaluations of Alternative Intersections

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Suggested Citation:"Appendix H - Summary of Safety Evaluations of Alternative Intersections." National Academies of Sciences, Engineering, and Medicine. 2020. Alternative Intersection Design and Selection. Washington, DC: The National Academies Press. doi: 10.17226/25812.
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Suggested Citation:"Appendix H - Summary of Safety Evaluations of Alternative Intersections." National Academies of Sciences, Engineering, and Medicine. 2020. Alternative Intersection Design and Selection. Washington, DC: The National Academies Press. doi: 10.17226/25812.
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Suggested Citation:"Appendix H - Summary of Safety Evaluations of Alternative Intersections." National Academies of Sciences, Engineering, and Medicine. 2020. Alternative Intersection Design and Selection. Washington, DC: The National Academies Press. doi: 10.17226/25812.
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Suggested Citation:"Appendix H - Summary of Safety Evaluations of Alternative Intersections." National Academies of Sciences, Engineering, and Medicine. 2020. Alternative Intersection Design and Selection. Washington, DC: The National Academies Press. doi: 10.17226/25812.
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Suggested Citation:"Appendix H - Summary of Safety Evaluations of Alternative Intersections." National Academies of Sciences, Engineering, and Medicine. 2020. Alternative Intersection Design and Selection. Washington, DC: The National Academies Press. doi: 10.17226/25812.
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Suggested Citation:"Appendix H - Summary of Safety Evaluations of Alternative Intersections." National Academies of Sciences, Engineering, and Medicine. 2020. Alternative Intersection Design and Selection. Washington, DC: The National Academies Press. doi: 10.17226/25812.
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Suggested Citation:"Appendix H - Summary of Safety Evaluations of Alternative Intersections." National Academies of Sciences, Engineering, and Medicine. 2020. Alternative Intersection Design and Selection. Washington, DC: The National Academies Press. doi: 10.17226/25812.
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204 Summary of Safety Evaluations of Alternative Intersections A P P E N D I X H Table H-1. Summary of safety evaluations for roundabouts Location Studied Key Findings Reference Colorado (3 intersections) Reductions in crashes or number of injuries Felsberg, Holt, and Ullevig and DiExSys 2018 Georgia Crash reductions: 37% to 48% (total), 51% to 60% (fatal/injury) Gbologah et al. 2019 Maine Crash reductions: 48% (total), 69% (injury) Maine Department of Transportation (DOT) n.d. Minnesota Crash reduction: 80% (fatal/injury) (single-lane roundabouts) Leuer 2014 Minnesota Crash reduction: 80% (fatal/injury) Leuer 2017 and Leuer 2018 Missouri (single-lane roundabout terminals at interchanges) Crash reductions: 24% (total), 33% (fatal/injury) Claros et al. 2018 Missouri (dual-lane roundabout terminals at interchanges) Crash increases: 33% (total), 29% (fatal/injury) Claros et al. 2018 North Carolina Crash reductions: 46% (total), 75% (fatal/injury), 76% (frontal impact) North Carolina DOT n.d.a

Summary of Safety Evaluations of Alternative Intersections 205 Location Studied Key Findings Reference Pennsylvania Crash reduction: 47% (total); Fatalities reduced by 100% Pennsylvania DOT 2018 Wisconsin Reductions in fatal/injury crashes at two-thirds of sites Wisconsin Traffic Safety and Operations Laboratory 2013

206 Alternative Intersection Design and Selection Table H-2. Summary of safety evaluations for diverging diamond interchanges (DDIs) Location Studied Key Findings Reference Minnesota Crash Modification Factors (CMFs): 0.42 to 0.48 (total) Walls et al. 2018 Missouri (project level) Approx. project level crash reductions: 41% to 48% (total), 59% to 63% (fatal/injury) Claros et al. 2015 Missouri (site specific: ramp terminals) CMFs: 0.625 (total), 0.45 (fatal/injury) Claros, Edara, and Sun 2017b Missouri (I-44 and Route 13) Crash reductions (first year): 46% (total), 72% (left turn right angle) Chilukuri et al. 2011 Missouri Presence of DDI did not affect safety on adjacent intersections and speed- change lanes Claros, Edara, and Sun 2017a Multiple states CMFs: 0.67 (total), 0.59 (fatal/injury) Hummer et al. 2016 Multiple states CMFs: 0.633 (total), 0.461 (fatal/injury) Nye et al. 2019 Utah CMFs (project level): 0.64-0.69 (total), 0.43-0.44 (fatal/injury); CMFs (site specific): 0.50-0.74 (total), 0.32-0.58 (fatal/injury) Song and Lloyd 2018 Utah (I-15 at Pioneer Crossing) Crash reduction: 45% (total) Utah DOT 2014

Summary of Safety Evaluations of Alternative Intersections 207 Table H-3. Summary of safety evaluations of superstreets Location Studied Key Findings Reference Florida Crash reductions were achieved Lu et al. 2001 Louisiana Crash reductions: 29% (total), 100% (fatal) Sun et al. 2019 Maryland Crash reductions: 28% to 40% (total); reduction in crash severity Inman and Haas 2012 Maryland (1 intersection), North Carolina (3 intersections) Crash reductions were achieved Hochstein et al. 2009 Minnesota Crash reductions: 100% (fatal/injury right-angle), 77% (all right-angle, 50% (injury) Leuer and Fleming 2017 Minnesota Did not find that frequency of truck crashes increased after superstreet installation Hawkins et al. 2015 Missouri Crash reductions: 31% (total), 64% (fatal/injury) Edara et al. 2015 Missouri Major road sideswipe and major road rear-end most common crash types at superstreets. Crash rates decreased as distance to U-turn increased. Claros, Zhu, Edara, and Sun 2017 North Carolina Inconclusive (signalized); Significant crash reductions for total and fatal/injury (unsignalized) Hummer et al. 2010 North Carolina Crash reductions: 59% (total), 71% (fatal/injury), 80% (frontal impact) (unsignalized) North Carolina DOT n.d.b North Carolina CMF: 0.54 (total) (unsignalized) Ott et al. 2012 North Carolina (NC- 24/87 at HM Cagle Drive / Linden Oaks Parkway) Total crashes increased 16%; Crash severity index decreased 81% Schronce 2016 Wisconsin Crash reductions: 21% (total), 89% (fatal/injury) Porter and Nelson 2018

208 Alternative Intersection Design and Selection Table H-4. Summary of safety evaluations for other types of alternative intersections Intersection Type Location Studied Key Findings Reference Continuous flow intersection (CFI) Texas (2 intersections) No significant difference; Crash frequency increased in first year at Location 2 Qi et al. 2018 CFI Utah Safety at CFI comparable to other intersection types Utah DOT 2013 Continuous green-T (CGT) Florida CMFs for conversion of CGT back to conventional intersection: 0.539 (total), 0.444 (fatal/injury), 0.564 (PDO) Lee et al. 2019 CGT Florida, South Carolina CMFs: 0.958 (total), 0.846 (fatal/injury), 0.920 (rear-end, angle, and sideswipe) Donnell et al. 2016 CGT Multiple states Crash reductions: 60% (total), 70% (injury) FHWA 2010 Jughandle New Jersey Lower crash rates for PDO, fatal/injury, and head-on Jagannathan et al. 2006 Median U-turn (MUT) Michigan Inconclusive (signalized); Significant crash reductions for fatal/injury (unsignalized); More PDO crashes when volumes >15,000 vehicles per day (vpd) (unsignalized) Kay et al. 2019 MUT Michigan MUTs can reduce crash severity by 30% to 60% Michigan DOT n.d. MUT Michigan Crash reductions were achieved Rista et al. 2018 Quadrant Roadway Intersection (QRI) North Carolina (US-21 and SR-73) Total crashes increased 31%, Crash severity index increased 1% Simpson 2017 Single point diamond interchange (SPDI) Arizona No significant difference in crash rates between Tight diamond interchange (TDI) and SPDI with frontage road Lee et al. 2002 SPDI Washington No significant difference in total crashes, reduction in injury crashes Bared et al. 2005

Abbreviations and acronyms used without definitions in TRB publications: A4A Airlines for America AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACI–NA Airports Council International–North America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FAST Fixing America’s Surface Transportation Act (2015) FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers MAP-21 Moving Ahead for Progress in the 21st Century Act (2012) NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005) TCRP Transit Cooperative Research Program TDC Transit Development Corporation TEA-21 Transportation Equity Act for the 21st Century (1998) TRB Transportation Research Board TSA Transportation Security Administration U.S. DOT United States Department of Transportation

A lternative Intersection D esign and Selection N CH RP Synthesis 550 TRB TRA N SPO RTATIO N RESEA RCH BO A RD 500 Fifth Street, N W W ashington, D C 20001 A D D RESS SERV ICE REQ U ESTED N O N -PR O FIT O R G . U .S. PO STA G E PA ID C O LU M B IA , M D PER M IT N O . 88 ISBN 978-0-309-48138-0 9 7 8 0 3 0 9 4 8 1 3 8 0 9 0 0 0 0

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State departments of transportation often encounter public resistance to alternative intersections, with 86% of respondents in a new survey of state DOTs agreeing or strongly agreeing that public resistance hinders their implementation. Public resistance can vary among projects based on intersection type and whether the project was initiated at the local or state level.

The TRB National Cooperative Highway Research Program's NCHRP Synthesis 550: Alternative Intersection Design and Selection documents the evaluation and selection processes within state departments of transportation (DOTs) for intersection projects.

Roundabouts are the most widely implemented type of alternative intersection. Ninety percent of state DOTs that responded to the synthesis survey reported having at least one roundabout in their jurisdiction open and operational. Roundabouts also had the highest reported number of facilities in project development as 88% of respondents indicated there was at least one roundabout under development at their DOT.

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