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

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1 SUMMARY Finding effective and economical non-herbicide, long-term vegetation management strategies (VMSs) to reduce the need for recurring chemical and mechanical vegetation controls has been a challenge for departments of transportation (DOTs). Vegetation management at key roadside locations and roadside appurtenances involves the safety of the traveling public and maintenance personnel, environmental impacts, roadside aesthetics, and budget constraints. Data were compiled through a survey of practice and a review of relevant research and DOT documents and websites. The research focused on VMS issues such as effectiveness, longevity, initial construction costs, maintenance costs and requirements, safety, interaction with highway appurtenances, and aesthetic values. Researchers identified typical materials and VMS usage locations. The use of VMSs improves both worker and driver safety by minimizing worker exposure on the roadsides for recurring maintenance and reducing traffic diversions and delays for maintenance activities. The safety of maintenance personnel is directly related to the level of difficulty and/or time requirements for material installation, maintenance, and repair. Workers’ safety is greatly affected by increased exposure to traffic and other roadside hazards. The need for prolonged traffic controls necessary to complete the required tasks is an important consideration. Therefore, each VMS receives a level of difficulty rating of low, moderate, or high. This is not only indicative of the specific VMS material characteristics but also includes the relative level of worker safety and exposure during installation, maintenance, and repair. The VMS locations examined in this study include cable barriers, support posts and poles, edge of pavement, gore/median, guardrail, mow edge/strip, and slope/embankment. The VMS has three basic categories: impervious surfaces, pervious surfaces, and select vegetation establishment. VMSs are designed to cover the designated area and minimize maintenance activities, particularly adjacent to the travel lanes. VMSs applied in and around highway safety appurtenances should be done so cognizant of their effect on the performance of everything in the highway design environment. If a VMS is thought to possibly have a performance effect on a highway safety appurtenance, then consideration should be given to crash testing the VMS and safety appurtenance together as a system. As of January 1, 2011, all newly developed hardware must be tested using the Manual for Assessing Safety Hardware (MASH). Of particular interest to the application of VMSs, the Federal Highway Administration (FHWA) also issued a memorandum dated January 7, 2016, regarding the federal-aid eligibility of highway safety hardware after December 31, 2016. The following applies to VMSs: • FHWA will no longer issue eligibility letters for highway safety hardware that has not been successfully crash tested to the 2016 edition of MASH. • Modifications of eligible highway safety hardware must use criteria in the 2016 edition of MASH for reevaluation and/or retesting. • Non-significant modifications of eligible hardware that have a positive or inconsequential effect on safety performance may continue to be evaluated using finite element analysis.

2 Cost and worker safety are key issues for DOTs. Material choice needs to consider a broad range of issues that weigh material and installation costs versus maintenance worker exposure in high- traffic areas. Some VMSs may have a low initial cost but are labor intensive to install and maintain. Another consideration is the environmental impact of various VMSs. In environmentally sensitive areas where herbicide use is unacceptable, highly effective VMSs are a key decision factor over material and installation costs. Researchers used a web-based survey sent to all state DOT maintenance directors requesting information on current practices, institutional obstacles, and the concerns that DOTs have regarding VMS usage. Requested information included the DOT selection process for VMSs, innovative methods or technologies, and information on any additional guidance that is required. Seventeen states responded to the survey, with some states giving multiple responses based on regional differences. Survey results showed the most common VMS locations are at guardrails, cable barriers, and the edge of pavement. The most used VMSs reported by the respondents are minor concrete pavement, asphalt, gravel, and native and non-irrigation vegetation. Researchers found difficulty in gathering information because VMSs are often not specified as such. They are part of a greater design/construction element. For example, placing concrete under guardrail is part of many guardrail construction manuals and/or specifications. However, concrete at similar locations is generally not labeled as a VMS. Researchers were tasked with developing an Interactive Selection Tool to provide information on non-herbicide, long-term VMSs for roadsides and roadside appurtenances that are appropriate for new and retrofit construction. The development of the Interactive Selection Tool was based on the information collected from the literature review, survey of practice, and follow-up interviews with select DOTs. Twenty VMSs were identified for inclusion in the tool (see Chapter 5 and Appendix C for details on each VMS). There is a growing body of research and project implementation regarding the use of VMSs. While there are emerging products within the industry, few studies have been conducted on product performance as it relates to non-herbicide, long-term VMSs. However, for many DOTs, implementation and/or demonstration projects using new techniques and/or products are conducted internally and may not be made publicly available through typical website searches. This project was also tasked with identifying knowledge gaps and possible updates/additions to the American Association of State Highway and Transportation Officials Guidelines for Vegetation Management. The following sections describe this task. RESILIENCE Transportation resilience is the ability of a transportation system to function at an acceptable rate in the event of extreme weather events, major crashes, and equipment or infrastructure failures. Quick recovery of a system is critical to avoid long-term effects. State DOTs need information on VMSs that can increase the resilience of transportation facilities and the transportation system.

3 POLLINATORS In June 2014, the White House issued the Presidential Memorandum (PM), “Creating a Federal Strategy to Promote the Health of Honeybees and Other Pollinators.” The PM directs federal agencies to take additional steps to improve habitat for pollinators, including honeybees, native bees, birds, bats, and butterflies—critical contributors to our nation’s economy, food system, and environmental health. With millions of acres of highway roadsides, state and local transportation agencies own or control land with the ability to conserve and/or create important habitat corridors that link otherwise fragmented pollinator habitat. State DOTs need information on how to update their vegetation management policies, practices, and standards to align with the PM on pollinators. HERBICIDES Herbicide-resistant weeds are becoming problematic for roadside vegetation managers. Herbicide manufacturers are changing the basic chemistry to combat resistance. This is becoming more and more difficult as some chemicals are being deleted from the roadside maintenance arsenal. The U.S. Department of Agriculture has taken over all aspects of herbicide control (i.e., licensing, training, etc.). State DOTs need information on how to respond to herbicide resistance and the current regulatory environment. MANAGED SUCCESSION Many DOTs are implementing more non-mow or reduced-mow areas within their rights of way due to the cost, safety, and environmental benefits of managed succession of roadside vegetation outside the safety clear zone. Many of the benefits fall under ecosystem services (ESs). These ES benefits include ecosystem diversity, stormwater quantity and quality management, carbon sequestration, erosion control, pollinator corridor development, wildlife habitat, and aesthetics. State DOTs need information on how managed succession can be used to advance environmental benefits, deliver ESs, and better manage roadside vegetation.