STATUS: Research is complete. Final report is under review.
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. Roadside vegetation can be controlled using herbicides, mowers, and other equipment or by permanent vegetation controls.
Permanent vegetation controls are designed to prevent or significantly retard the growth of unwanted vegetation. Using a permanent vegetation control decreases the need for recurring chemical and mechanical vegetation control, thus reducing recurring maintenance costs, highway worker exposure to traffic, impacts to the environment and cultural resources, and maintenance-related delays to the traveling public. Additional advantages include maintaining the integrity of highway surfaces by controlling erosion and damage to the pavement structure from encroaching roots and water intrusion. However, permanent vegetation controls vary in their effectiveness, longevity, initial construction costs, maintenance requirements, and aesthetic values. Some treatments may also affect the safety performance of highway appurtenances, such as guardrails, cable barriers, and signs. For example, continuous asphalt or concrete may potentially result in pocketing or rupture of strong-post guardrails.
The American Association of State Highway and Transportation Officials (AASHTO) Guidelines for Vegetation Management (Guidelines), published in 2011, collected and compiled information about roadside vegetation management. Many state departments of transportation (DOTs) utilize the Guidelines in their vegetation management programs. Chapter 12 of the Guidelines cataloged a range of permanent vegetation controls (including concrete and asphalt surface treatments, mats, mulches, and competitive vegetation); however, information for some situations is missing, for example, controls for use with cable barriers. Furthermore, research and agency experience have yielded additional methods and technologies, as well as insights into the effectiveness of permanent vegetation controls and under what conditions a particular control is appropriate. Therefore, updated guidance on the selection of appropriate permanent vegetation controls is needed.
The objective of this research is to produce up-to-date guidance for transportation agencies for selecting appropriate permanent vegetation controls that will be effective in preventing or significantly retarding the growth of unwanted vegetation around roadside appurtenances and along roadsides. The guidance will identify controls appropriate for new construction and for existing facilities. In addition, the guidance will describe how to select effective permanent vegetation controls that also address traveler and highway worker safety and costs of construction and maintenance, as well as minimize adverse environmental impacts.