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

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4 CHAPTER 1. INTRODUCTION DOTs have historically incorporated a range of roadside vegetation management techniques within the right of way (ROW) to maintain adequate sight distance, reduce invasive and nuisance weeds, provide roadside aesthetics, and protect roadway infrastructure and roadside appurtenances. Many of these techniques are often included as part of the respective agency’s Integrated Vegetation Management Plan. The most used methods for vegetation control include mowing and other mechanical removal techniques, and chemical treatments such as herbicides. The American Association of State Highway and Transportation Officials (AASHTO) published Guidelines for Vegetation Management in 2011 to assist DOTs with their vegetation management programs (AASHTO 2011a). Specifically, DOTs seek more effective and economical non-herbicide, long-term VMSs to reduce the need for recurring chemical and mechanical vegetation controls. This action may help DOTs reduce maintenance costs, safety hazards for roadway users and maintenance personnel, exposure to herbicides, environmental and cultural impacts, and maintenance-related delays to the traveling public. Transportation agencies generally categorize their roadside management strategies according to the different management zones. Figure 1 shows the respective roadside zones. Zone 1 is considered the operational zone, and its management includes pavement preservation, erosion control, safety-related issues such as sight distance, and maintenance of roadside appurtenances and signs. Zone 1 is the main area of concern for this project and is often a vegetation-free zone. However, VMSs are also used along roadsides, in medians and gores, and in other areas with appurtenances such as cable barrier systems requiring control measures to ensure that infrastructure has minimal maintenance requirements. Figure 1. Roadside Management Zones (Adapted from Washington State Department of Transportation 2015). The importance of managing unwanted vegetation in Zone 1 and those areas containing barriers, support posts and poles, and other appurtenances lies in the safety risks for maintenance personnel and the potential damage caused by unwanted vegetative growth. Maintenance personnel’s safety is greatly affected by increased exposure to traffic and other roadside hazards. Unwanted vegetation at the edge of pavement can cause a buildup of litter, debris, sand (from

5 winter operations), and sediment that impedes stormwater runoff from leaving the roadway and provides fuel for roadside fires. RESEARCH APPROACH The goal of the research conducted for National Cooperative Highway Research Program (NCHRP) Project 14-41 is to produce up-to-date and user-friendly guidance for transportation agencies to facilitate the selection of appropriate non-herbicide, long-term VMSs that will be effective in preventing or significantly retarding the growth of unwanted vegetation around roadside appurtenances and along roadsides. The project goal was accomplished through two objectives. The first objective was to conduct a thorough assessment of VMS usage and practices in the United States. This assessment included relevant research regarding effectiveness, longevity, initial construction costs, maintenance requirements, safety performance of highway appurtenances, and aesthetic values. Researchers gathered information on VMS usage through a detailed review of the literature, targeted interviews with technical experts, a web-based survey of transportation practitioners, and in- depth interviews with practitioners that have piloted or implemented additional methods, technologies, or applications. The second objective was to develop an interactive tool to assist agencies in the selection of an appropriate VMS. The Interactive Selection Tool will help agencies evaluate the potential costs and benefits of each VMS for a given scenario. The development of the tool was based on the information collected from the literature review, a survey of practice, and follow-up interviews with select DOTs. This tool employs a decision algorithm to advise the user of an appropriate VMS treatment for the specific conditions. The tool can be downloaded and used in a self- contained folder format. Chapter 5 provides more information, and Appendix B provides the user manual and instructions for downloading and extracting the files. RESEARCH METHODOLOGY The research approach for this project included a detailed literature review, a review of state transportation agency VMS practices, and a survey of practice with select follow-up interviews. The identification and development of guidance material involved the following five tasks: • Task 1: Project Management. The objectives of this task were to ensure that the research was conducted as defined in the detailed work plan within the agreed-upon time and resources and to effectively communicate with the NCHRP technical representative regarding the direction of the project along with progress updates. • Task 2: Conduct Literature Review. This task objective was to document the state of the practice through a review of online documents and to review the literature on the effectiveness, longevity, initial construction costs, maintenance requirements, site conditions, ecological and climate conditions, and aesthetic value of VMS treatments and their effect on the safety performance of highway appurtenances, such as guardrails, cable barriers, and signs.

6 • Task 3: Conduct Web-Based Survey and Practitioner Interviews. The objective of this task was to supplement the information gathered in Task 2. Specifically, the research team aimed to collect information on current practices, institutional obstacles, issues, and concerns agencies have regarding VMS treatments. The research team also identified additional methods and technologies that DOTs are piloting or experimenting with, additional guidance required, and how DOTs can use the findings from this research. • Task 4: Develop Interactive Selection Tool. The objective of Task 4 was to develop the Interactive Selection Tool to provide step-by-step guidelines for transportation agencies to identify and select non-herbicide VMSs. The development of the Interactive Selection Tool was informed by and based on the information collected in Tasks 2 and 3. • Task 5: Prepare Final Deliverables. The objective of this task was to prepare the final project documentation, which includes this report documenting the research, the Interactive Selection Tool, and a graphic presentation of long-term non-herbicide VMSs. TERMINOLOGY Researchers found many common terms applied in the topic area of non-herbicide, long-term VMSs, roadsides, and roadside appurtenances. Table 1 defines these terms for use throughout the remainder of this report. Table 1. Terminology Related to VMSs. Term Definition Guardrail “A guardrail is a safety barrier intended to shield a motorist who has left the roadway. Guardrails can make roads safer and lessen the severity of crashes. The guardrail can operate to deflect a vehicle back to the roadway, slow the vehicle down to a complete stop, or, in certain circumstances, slow the vehicle down and then let it proceed past the guardrail” (FHWA n.d.). Strong post guardrail “The most widely used barrier—the strong post W-beam guardrail identified as SGR-04 in the Standardized Highway Barrier Hardware Guide (TF 13). (The term guardrail, and in some states guiderail, is commonly used either for just W-beam barriers or for barriers in general; for future use in this guide, the term W-beam guardrail will refer to the strong post W-beam barrier system.) The standard strong post W-beam guardrail consists of a W-beam rail element and strong posts (wood or steel) spaced at 6 ft 3 in with the rail blocked out from the posts.” The wood post is typically a nominal 6 inches by 8 inches by 72 inches, and the steel post is W6x8.5 or W6x9 and 72 inches long. The W-beam is typically 12 gauge (Fitzgerald 2008). Cable barrier Includes median and roadside cable barrier systems. “Cable barriers are softer, resulting in less impact force and redirection, are more adaptable to slopes typically found in medians, and can be installed through less invasive construction methods” (FHWA 2022). Cable barriers typically have higher deflections when impacted than guardrail. Cable barrier installations can vary in the number of cables and post spacing used. More cables and closer post spacing will result in a smaller deflection and higher impact forces when struck.

7 Support posts and poles Any post or roadside appurtenance such as signs, luminaire supports and poles, lights, outdoor advertising, etc. requiring a VMS treatment at the base. Edge of pavement The interface where the roadway edge meets the adjacent material. Gore/median A gore area is located where roads merge or split. A median is the area separating opposing traffic lanes. These two categories are grouped due to similar characteristics for choosing a VMS. Mow edge/strip A VMS strip placed at the edge of a noise wall, roadside appurtenance, etc. that facilitates mowing. The terms edge and strip are often used interchangeably. Slope/embankment Areas where the roadside rises or falls from the roadway elevation. The degree of steepness is site specific.