Permanent vegetation control (barriers) is a group of vegetation control methods that use inert surface materials to prevent or significantly retard the growth of unwanted vegetation. Existing guidelines for this treatment are found in Guidelines for Vegetation Management, March 2011 by AASHTO. However, the information needs to be updated as new and better technology and methods have become available since 2011. Using permanent vegetation control reduces the need for chemical and manual vegetation control and reduces worker exposure to traffic. Permanent vegetation barriers need to prevent erosion, protect the integrity of highway surfaces, and protect nearby sensitive environmental resources (e.g., endangered species, other sensitive animals and plants, archaeological sites, Native American gathering sites, and environmental mitigation sites). Control of vegetation along roadsides is required for fire prevention, providing adequate sight distance, facility inspection needs, reducing invasive and nuisance weeds, promoting roadside aesthetics, and protecting highway appurtenances such as guardrails, cable barriers, and signs. Locations where permanent vegetation control is particularly important include, but are not limited to, guard rails, cable barriers, signs, road edges, and other roadside assets. Permanent vegetation control is also necessary to sustain the transportation system and promote both worker and traveler safety. Therefore, an approach to permanent vegetation control is desired that effectively suppresses weeds, is simple and economical to use, does not interfere with the performance of the guardrail, cable barrier, and roadside signs, allows for easy repairs, can be applied to new and existing roadside safety appurtenances, and is aesthetically pleasing. Ideally, this permanent vegetation control treatment can also be used for other applications such as road edges, gore areas, maintenance access roads, and maintenance vehicle pullouts.
The objectives of this research are to: (1) update Section 12.0, Permanent Vegetation Control (Barriers), in the AASHTO Guidelines for Vegetation Management, March 2011; (2) provide new guidance on permanent vegetation control for cable barriers and roadside signs; and (3) review the entire guide for any other pertinent updates regarding vegetation management that have occurred since its publication.