Long-Term Vegetation Management Strategies for Roadsides and Roadside Appurtenances (2023)

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NCHRP Web-Only Document 350 Long-Term Vegetation Management Strategies for Roadsides and Roadside Appurtenances Jett McFalls Beverly Storey Subasish Das John Habermann D. Lance Bullard, Jr. Texas A&M Transportation Institute College Station, TX Conduct of Research Report for NCHRP Project 14-41 Submitted January 2023 © 2023 by the National Academy of Sciences. National Academies of Sciences, Engineering, and Medicine and the graphical logo are trademarks of the National Academy of Sciences. All rights reserved. NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Systematic, well-designed, and implementable research is the most effective way to solve many problems facing state departments of transportation (DOTs) administrators and engineers. Often, highway problems are of local or regional interest and can best be studied by state DOTs individually or in cooperation with their state universities and others. However, the accelerating growth of highway transportation results in increasingly complex problems of wide interest to highway authorities. These problems are best studied through a coordinated program of cooperative research. Recognizing this need, the leadership of the American Association of State Highway and Transportation Officials (AASHTO) in 1962 initiated an objective national highway research program using modern scientific techniques—the National Cooperative Highway Research Program (NCHRP). NCHRP is supported on a continuing basis by funds from participating member states of AASHTO and receives the full cooperation and support of the Federal Highway Administration (FHWA), United States Department of Transportation, under Agreement No. 693JJ31950003. COPYRIGHT INFORMATION Authors herein are responsible for the authenticity of their materials and for obtaining written permissions from publishers or persons who own the copyright to any previously published or copyrighted material used herein. Cooperative Research Programs (CRP) grants permission to reproduce material in this publication for classroom and not-for-profit purposes. Permission is given with the understanding that none of the material will be used to imply TRB, AASHTO, APTA, FAA, FHWA, FTA, GHSA, or NHTSA endorsement of a particular product, method, or practice. It is expected that those reproducing the material in this document for educational and not-for-profit uses will give appropriate acknowledgment of the source of any reprinted or reproduced material. For other uses of the material, request permission from CRP. DISCLAIMER The opinions and conclusions expressed or implied in this report are those of the researchers who performed the research. They are not necessarily those of the Transportation Research Board; the National Academies of Sciences, Engineering, and Medicine; the FHWA; or the program sponsors. The Transportation Research Board does not develop, issue, or publish standards or specifications. The Transportation Research Board manages applied research projects which provide the scientific foundation that may be used by Transportation Research Board sponsors, industry associations, or other organizations as the basis for revised practices, procedures, or specifications. The Transportation Research Board, the National Academies, and the sponsors of the National Cooperative Highway Research Program do not endorse products or manufacturers. Trade or manufacturers’ names appear herein solely because they are considered essential to the object of the report. The information contained in this document was taken directly from the submission of the author(s). This material has not been edited by TRB.

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C O O P E R A T I V E R E S E A R C H P R O G R A M S CRP STAFF FOR NCHRP WEB-ONLY DOCUMENT 350 Christopher J. Hedges, Director, Cooperative Research Programs Waseem Dekelbab, Deputy Director, Cooperative Research Programs, and Manager, National Cooperative Highway Research Program Sid Mohan, Associate Program Manager, Implementation and Technology Transfer, National Cooperative Highway Research Program Ann Hartell, Senior Program Officer Dajaih Bias-Johnson, Senior Program Assistant Natalie Barnes, Director of Publications Heather DiAngelis, Associate Director of Publications Jennifer Correro, Assistant Editor NCHRP PROJECT 14-41 PANEL Field of Maintenance—Area of Maintenance of Way and Structures Kris Gade, Arizona Department of Transportation, Tucson, AZ (Chair) Robert W. Bielenberg, University of Nebraska, Lincoln, Lincoln, NE Jack D. Broadbent, California Department of Transportation (CALTRANS), Sacramento, CA Brian D. Burk, Travis County, Austin, TX Robert N. Graeff, Illinois Department of Transportation, Carbondale, IL Mary Ellen Papin, New York State Department of Transportation, Rochester, NY Adam S. Weiser, WRA, Wilmington, DE Lana Lau, FHWA Liaison (formerly) ACKNOWLEDGMENTS The research reported herein was performed under NCHRP Project 14-41 by the Texas A&M Transportation Institute, a member of The Texas A&M University System. The authors thank the state departments of transportation for their participation in the survey of practice and case example interviews. The authors also thank Roger Bligh and Lance Bullard of the Texas A&M Transportation Institute’s Roadside Safety and Physical Security Division for their expertise and contributions to this project.

iv FOREWORD Ann Hartell NCHRP Web-Only Document 350 presents information on strategies that control the establishment and growth of roadside vegetation over an extended period, reducing the need for herbicides, mowing, and other mechanical controls. The report and accompanying resources will be of interest to those responsible for designing and maintaining the roadside environment. Control of vegetation along roadsides is required for fire prevention, adequate sight distance, facility inspection needs, reduction of invasive and nuisance weeds, roadside aesthetics, and protection of roadside appurtenances, such as guardrails, cable barriers, and sign posts. Roadside vegetation can be controlled using herbicides, mowers, and other equipment or, alternatively, by strategies designed to prevent or significantly retard the growth of unwanted vegetation for longer periods. These long-term vegetation management strategies include asphalt or concrete surface treatments, mats, mulches, or competitive vegetation. Long-term vegetation management strategies that decrease the need for routine chemical and mechanical vegetation control can reduce recurring maintenance costs, highway worker exposure to traffic, impacts to the environment and cultural resources, and maintenance-related delays to the traveling public. However, these strategies vary in their effectiveness, longevity, initial construction costs, maintenance requirements, and aesthetic values. A critical consideration is how any strategy may affect the safety performance of highway appurtenances, such as guardrails, cable barriers, and sign posts. This is because surface and soil conditions are part of the design of roadside safety appurtenances, so designers need to understand any potential interactions between design elements that can affect safety performance. The American Association of State Highway and Transportation Officials (AASHTO) Guidelines for Vegetation Management, published in 2011, collected and compiled information about roadside vegetation management. However, information on long-term strategies was limited and did not fully address how these design elements can interact with some common roadside appurtenances, such as cable barriers. Furthermore, recent field research and on-going experience from state department of transportation (DOTs) offers new insights into installation requirements, costs, effectiveness, and aesthetics. NCHRP Web-Only Document 350 provides up-to-date information on long-term vegetation management strategies for new construction and retrofits to existing facilities in a range of contexts. The report and accompanying materials describe a range of strategies along with information about effectiveness, relative costs, aesthetics, and longevity. Because safety—for motorists, construction workers, and maintenance crews—is an imperative for roadside design, the report includes information on potential interactions between vegetation management strategies and roadside appurtenances as well as construction and maintenance requirements that affect worker exposure to traffic.

v The research was conducted by Texas A&M Transportation Institute (TTI). The research effort included a review of relevant research and design guidelines along with a survey of practitioners. The report is accompanied by a downloadable interactive tool for selecting vegetation management strategies based on critical inputs about the location. Also available is a tabular presentation with 20 strategies and key considerations for each, designed for quick, desktop reference. A set of presentation slides with speaker notes summarizes the project. These materials are available on the TRB website and can be found by searching for “NCHRP Web- Only Document 350”.

vi CONTENTS List of Figures ............................................................................................................................... vii List of Tables ............................................................................................................................... viii Summary ......................................................................................................................................... 1 Resilience .................................................................................................................................... 2 Pollinators ................................................................................................................................... 3 Herbicides ................................................................................................................................... 3 Managed Succession ................................................................................................................... 3 Chapter 1. Introduction ................................................................................................................... 4 Research Approach ..................................................................................................................... 5 Research Methodology ............................................................................................................... 5 Terminology ................................................................................................................................ 6 Chapter 2. Literature Review .......................................................................................................... 8 VMSs and Performance of Highway Safety Appurtenances ...................................................... 9 Longitudinal Barriers ........................................................................................................ 10 Terminals and Crash Cushions ......................................................................................... 13 Truck- and Trailer-Mounted Attenuators and Portable Work-Zone Traffic Control Trailers ........................................................................................................................ 14 Support Structures, Work-Zone Traffic Control Devices, Breakaway Utility Poles, and Longitudinal Channelizers ................................................................................... 14 Roadside Geometric Features and Pavement Discontinuities .......................................... 16 Summary ........................................................................................................................... 16 Leave-Outs ................................................................................................................................ 17 Non-herbicide, Long-Term VMSs ............................................................................................ 19 Impervious VMS Treatments ............................................................................................ 19 Pervious VMS Treatments ................................................................................................ 25 Select Vegetation Establishment ....................................................................................... 28 Comparison of Commonly Used VMSs ........................................................................... 30 Innovative/Alternative VMSs ........................................................................................... 31 Transportation Agency Research .............................................................................................. 32 Delaware Department of Transportation .......................................................................... 32 Georgia Department of Transportation ............................................................................. 35 Iowa Department of Transportation .................................................................................. 35 Texas Department of Transportation ................................................................................ 35 Washington State Department of Transportation ............................................................. 36 Summary ................................................................................................................................... 38 Chapter 3. State Transportation Agency Practices ....................................................................... 40 Survey of Practice ..................................................................................................................... 40 Practitioner Survey Results ....................................................................................................... 43 Summary of Survey Results.............................................................................................. 49 Other State DOT Practices that Perform as VMSs ................................................................... 49 Chapter 4. Case Examples ............................................................................................................ 51 California Department of Transportation ................................................................................. 51 Idaho Transportation Department ............................................................................................. 52 Rhode Island Department of Transportation ............................................................................ 53

vii Texas Department of Transportation ........................................................................................ 53 Chapter 5. Conclusions ................................................................................................................. 54 Selecting a VMS ....................................................................................................................... 54 VMS Treatment Selection Using Interactive Selection Tool ................................................... 55 VMS Location ................................................................................................................... 56 Level of Aesthetics ........................................................................................................... 56 Information Sheets ............................................................................................................ 57 Relative Initial Cost .......................................................................................................... 57 Effective Longevity .......................................................................................................... 58 Level of Difficulty ............................................................................................................ 58 Advantages/Limitations/Common Problems .................................................................... 58 VMSs Included in Tool ..................................................................................................... 58 Alternative and Innovative VMSs .................................................................................... 59 Further Additional Updates to AASHTO Guidelines for Vegetation Management ................. 59 Resilience .......................................................................................................................... 60 Pollinators ......................................................................................................................... 60 Herbicides ......................................................................................................................... 60 Managed Succession ......................................................................................................... 60 References ..................................................................................................................................... 61 Appendix A: TxDOT Vegetation Management Strategy Installation .......................................... 66 Appendix B: Interactive Selection Tool User Manual .................................................................. 67 Appendix C: Interactive Selection Tool Information Sheets ........................................................ 73 Appendix D: Pennsylvania Department of Transportation Recycling Material Brief: Crushed Glass Fact Sheet.................................................................................................. 97 Appendix E: Roadside Safety Overview .................................................................................... 101

viii LIST OF FIGURES Figure 1. Roadside Management Zones (Adapted from Washington State Department of Transportation 2015). .............................................................................. 4 Figure 2. AASHTO RDG Guardrail Post Detail in Mow Strip Application (AASHTO 2011b). .............................................................................................. 12 Figure 3. Guardrail Post Details in Rock Formation (AASHTO 2011b). .................................... 13 Figure 4. Multidirectional Slip Base for Small Signs (AASHTO 2011b). ................................... 15 Figure 5. Example of a Cast Aluminum Frangible Luminaire (AASHTO 2011b). ..................... 16 Figure 6. Example of a Frangible Coupling Design (AASHTO 2011b). ..................................... 16 Figure 7. Weed Growth at the Edge of Pavement (Barton and Budischak 2013). ....................... 17 Figure 8. Minor Concrete Used for Vegetation Management (Caltrans 2017b). ......................... 20 Figure 9. Standard Concrete Pavement Uses (Sheikh et al. 2019). .............................................. 21 Figure 10. Asphalt under Cable Barrier System. .......................................................................... 21 Figure 11. Stamped Asphalt Concrete at Roundabout (Pattern Paving Products 2016). .............. 22 Figure 12. Asphalt Composite Treatment at Guardrail System (Caltrans 2017d). ....................... 22 Figure 13. Modular Paving Units in Median (TxDOT 2017). ...................................................... 23 Figure 14. Rock Blanket Installations (Diversified Landscape Company 2016, Caltrans 2015). ........................................................................................................................ 24 Figure 15. Rubber Weed Mat (Caltrans 2017e). ........................................................................... 25 Figure 16. Aggregate Base (Meininger and Stokowski 2011). ..................................................... 25 Figure 17. Recycled Glass Cullet Mulch (Malcolm 2006). .......................................................... 26 Figure 18. Gravel Mulch Treatment at the Roadside. ................................................................... 27 Figure 19. Rock Slope Protection (Ohio Department of Transportation n.d., Indiana Department of Environmental Management 2007). .................................................. 27 Figure 20. Organic Mulch (Pacific Landscape Supply 2019). ...................................................... 28 Figure 21. Weed Control Fiber Mat (Caltrans 2017h). ................................................................. 28 Figure 22. Irrigated Ornamental Vegetation. ................................................................................ 29 Figure 23. Native Non-irrigated Vegetation. ................................................................................ 29 Figure 24. Concrete Canvas® GCCM Section (Concrete Canvas 2020). ..................................... 32 Figure 25. Concrete Cloth™ (Srinivas and Ravinder 2012). ........................................................ 32 Figure 26. Weed Control Barriers Evaluated in DelDOT Study (Barton and Budischak, 2013). ................................................................................................................... 33 Figure 27. TxDOT Demonstration Project Using Crumb Rubber VMS (TxDOT 2012). ............ 36 Figure 28. Cable Barrier and Roadside Vegetation (TxDOT 2008). ............................................ 36 Figure 29. Survey Responses by State. ......................................................................................... 41 Figure 30. Selection Tool Input Result Example. ......................................................................... 57

ix LIST OF TABLES Table 1. Terminology Related to VMSs. ........................................................................................ 6 Table 2. Comparison of Vegetation Management Strategies (Caltrans 2017, TxDOT 2018)................................................................................................................ 30 Table 3. DelDOT Weed Barrier and Competitive Vegetation Cost Comparison (Barton and Budischak 2013). ............................................................................ 34 Table 4. DelDOT VMS Suitability and Weed Control Rating (Barton and Budischak 2013). .............................................................................................................. 35 Table 5. WSDOT VMS Results (Willard et al. 2010). ................................................................. 37 Table 6. State DOT Survey Respondents. .................................................................................... 41 Table 7. Survey Questions. ........................................................................................................... 42 Table 8. Responses for Survey Questions 3 and 4. ....................................................................... 43 Table 9. Responses for Survey Question 5. .................................................................................. 44 Table 10. Responses for Survey Question 6. ................................................................................ 44 Table 11. Responses for Survey Question 7. ................................................................................ 45 Table 12. Responses for Survey Question 8. ................................................................................ 45 Table 13. Responses for Survey Question 9. ................................................................................ 45 Table 14. Responses for Survey Questions 10 and 11. ................................................................. 46 Table 15. Responses for Survey Question 12. .............................................................................. 46 Table 16. Responses for Survey Question 13. .............................................................................. 46 Table 17. Responses for Survey Question 14. .............................................................................. 47 Table 18. Responses for Survey Question 15. .............................................................................. 47 Table 19. Responses for Survey Question 16. .............................................................................. 47 Table 20. Responses for Survey Question 17. .............................................................................. 48 Table 21. Responses for Survey Question 19. .............................................................................. 48 Table 22. Responses for Survey Question 19. .............................................................................. 48 Table 23. Responses for Survey Question 20. .............................................................................. 49