PAVED SHOULDERS ON PRIMARY HIGHWAYS IN IOWA: AN A NALYSIS OF SHOULDER SURFACING CRITERIA, COSTS, AND BENEFITS FINAL REPORT Sponsored by the Office of Traffic and Safety of the Iowa Department of Transportation NOVEMBER 2001 CTRE Center for Transportation Research and Education ABSTRACT The value of providing paved shoulders adjacent to many higher volume road- ways has been accepted in many states across the country. Iowa’s paved shoul- der policy is considerably more conservative than neighboring states, particu- larly on rural four-lane and high-volume two-lane highways. The objectives of this research are to examine current design criteria for shoulders employed in Iowa and surrounding states, compare benefits and costs of alternative surface types and widths, and make recommendations based on this analysis for consideration in future design policies for primary highway in Iowa. The report finds that many safety and maintenance benefits would result from enhancing Iowa’s paved shoulder and rumble strip design practices for free- ways, expressways, and Super 2 highway corridors. The benefits of paved shoul- ders include reduced numbers of certain crashes, higher capacity potentials, reduced maintenance, enhanced opportunities for other users such as bicy- clists, and even possible increased longevity of pavements. Alternative paved shoulder policies and programming strategies are also offered, with detailed assessments of the benefits, costs, and budget impacts. The opinions, findings, and conclusions expressed in this publication are those of the authors and not necessarily those of the Iowa Department of Transportation. CTRE’s mission is to develop and implement innovative methods, materials, and technologies for improving transportation efficiency, safety, and reliability while improving the learning environment of students, faculty, and staff in transportation-related fields. PAVED SHOULDERS ON PRIMARY HIGHWAYS IN IOWA: AN ANALYSIS OF SHOULDER SURFACING CRITERIA, COSTS, AND BENEFITS FINAL REPORT Principal Investigator Reg Souleyrette Associate Professor of Civil and Construction Engineering, Iowa State University Associate Director for Transportation Planning and Information Systems, Center for Transportation Research and Education Co-Principal Investigators Tom McDonald Safety Circuit Rider, Center for Transportation Research and Education Zach Hans GIS Specialist, Center for Transportation Research and Education Ali Kamyab Research Scientist, Center for Transportation Research and Education Principal Contributor Tom Welch State Traffic Safety Engineer, Office of Traffic and Safety, Iowa Department of Transportation Research Assistant Brandon Storm Editor Mark Anderson-Wilk Sponsored by the Office of Traffic and Safety of the Iowa Department of Transportation Center for Transportation Research and Education Iowa State University Iowa State University Research Park 2901 South Loop Drive, Suite 3100 Ames, IA 50011-8632 Phone: 515-294-8103 Fax: 515-294-0467 www.ctre.iastate.edu/ NOVEMBER 2001 TABLE OF CONTENTS EXECUTIVE SUMMARY......................................................................................................... v Background ............................................................................................................................ v Study Scope...........................................................................................................................vi Research Findings..................................................................................................................vi National Studies.................................................................................................................vi Iowa Studies .....................................................................................................................vii Paved Shoulder Practices in Neighboring States....................................................................vii Alternative Paved Shoulder Policies......................................................................................vii Cost Assessment ..............................................................................................................viii Recommendations..................................................................................................................ix INTRODUCTION...................................................................................................................... 1 Background ............................................................................................................................ 1 Study Description ................................................................................................................... 1 LITERATURE REVIEW ........................................................................................................... 3 Shoulder Surface Type............................................................................................................ 3 Effects of Variable Shoulder Width, Paved and Unpaved........................................................ 4 Benefits of Rumble Strips with Paved Shoulders..................................................................... 6 Other Benefits of Paved Shoulders.......................................................................................... 6 SHOULDER DESIGN PRACTICES IN IOWA AND NEIGHBORING STATES ..................... 9 Iowa9 Illinois .................................................................................................................................. 10 Minnesota............................................................................................................................. 11 Missouri................................................................................................................................ 11 Nebraska............................................................................................................................... 12 South Dakota ........................................................................................................................ 13 Wisconsin............................................................................................................................. 14 COST ESTIMATIONS............................................................................................................. 15 Initial Costs........................................................................................................................... 15 Paved Shoulder versus Granular Shoulder......................................................................... 15 Initial Construction of Wider Pavement............................................................................. 16 Alternatives....................................................................................................................... 16 Maintenance Costs................................................................................................................ 18 ANALYSIS OF CRASH HISTORY IN IOWA ........................................................................ 20 COMPARATIVE ASSESSMENT USING CRASH DATA AND TRAFFIC VOLUME .......... 21 Roadway Designation ........................................................................................................... 21 Traffic Analysis .................................................................................................................... 21 Crash Analysis...................................................................................................................... 22 Comparative Assessments..................................................................................................... 23 ii SUPPLEMENTAL BENEFITS ................................................................................................ 32 CONCLUSIONS AND RECOMMENDATIONS..................................................................... 33 Conclusions .......................................................................................................................... 33 Recommendations.................................................................................................................34 ACKNOWLEDGMENTS ........................................................................................................ 35 REFERENCES......................................................................................................................... 36 APPENDIX A: COMPARATIVE IMPROVEMENT AND MAINTENANCE COSTS............ 39 APPENDIX B: PAVED SHOULDER ALTERNATIVES ........................................................ 40 iii LIST OF TABLES Table ES.1. Crash Rates for Rural Non-interstate and Interstate Freeways in Iowa....................vii Table ES.2. Paved Shoulder Practices in Iowa and Neighboring States ....................................viii Table ES.3. Alternative Paved Shoulder Width Standards........................................................viii Table ES.4. Incremental Construction Costs for Alternatives .....................................................ix Table ES.5. Cost to Replace Granular Shoulders on Existing Freeway/Expressway System.......ix Table 1. Literature Summary ......................................................................................................7 Table 2. Iowa Shoulder Design Practices ....................................................................................9 Table 3. Illinois Shoulder Design Practices ...............................................................................10