Departments of Transportation (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 are often included as part the respective agency’s Integrated Vegetation Management Plan. The most commonly used methods for vegetation control include mowing and other mechanical removal techniques, and chemical treatments such as herbicides. DOTs seek more non-herbicide, long-term vegetation management strategies (VMS) (minimum 3 to 5 years) that are effective and economical to reduce the need for routine chemical and mechanical vegetation controls. This action helps DOTs reduce maintenance costs, safety hazards for maintenance personnel, exposure to herbicides, environmental and cultural impacts, and maintenance related delays to the traveling public. The VMS can be categorized into three basic groups that include impervious surfaces, pervious surfaces, and select vegetation establishment.
This Selection Tool provides guidance for the selection of long-term vegetation management strategies for roadsides and roadside appurtenances. It should be noted that the Tool presented provides identification and guidance for the selection of non-herbicide, long-term vegetation management strategies for roadsides and roadside appurtenances. The VMS identified and presented do not represent specific design guidance for highway safety appurtenances, nor are they a substitute for any other highway design practice. The user should refer to the AASHTO’s Roadside Design Guide (RDG), Manual for Assessing Safety Hardware (MASH) and any specific state DOT practices for warrants, proper placement and maintenance of roadside safety appurtenances when applying these VMS (RDG 2011, MASH 2016). In addition, before applying any of the techniques described on a proprietary roadside safety hardware device (e.g., guardrail terminal, crash cushion, breakaway sign support, etc.) the manufacturer should be contacted to discuss the potential for the VMS to adversely affect the performance of their safety hardware device.
There are numerous considerations in choosing a VMS. Each site has specific needs that include the cost of initial installation, maintenance and repair. Other considerations are the overall life-cycle cost, suitability as new construction or retrofit, and effective longevity. The VMS locations were chosen for use in the Tool because they stand out in the literature, survey of practice and DOT documents as the most common areas where VMS are used. Other areas needing VMS are placed into each of these categories as they did not have any significant difference in use. The photos associated with each VMS selection are meant to represent VMS materials and are not indicative of any specific construction protocols or procedures. The Selection Tool requires three categories of user input based upon site specific conditions:
The site location and context may be a factor in choosing a VMS. Considerations include whether the site is urban, suburban or rural and the adjacent land use such as residential, commercial, industrial or agricultural. This choice is indicated by level of aesthetics and has a rating of high or standard. At high rating is generally indicative of an urban or suburban location or other locations where stakeholders expect a greater level of aesthetic treatment. A standard rating applies to all other VMS locations.
From the user selections, the Tool will generate commonly used VMS given the user inputs. If choosing guardrail as the VMS location and the VMS will be used under a strong post guardrail system, the user should refer to the link for STRONG POST GUARDRAIL USE WITH RIGID VMS MATERIALS information sheet for leave-out compliance requirements as this information sheet provides critical considerations regarding the interaction of rigid VMS materials and roadside safety appurtenances. Selecting the VMS photo links to an information sheet containing more specifics about that specific VMS such as:
Effective longevity is determined by the anticipated material life cycle and the level of maintenance routinely required of the specific VMS:
The cost for each VMS is determined as it relates to each of the other VMS provided. A high initial installation cost needs to be weighed against a low life-cycle cost and low maintenance costs. Costs for VMS very greatly based on quantity, availability and location. These relative costs were compiled from the literature, DOT documents and survey information. The relative installation cost determination is as follows:
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. As such, each VMS receives a level of difficulty rating of low, moderate or high. This not only indicative of the specific VMS material characteristics it also includes relative level of worker safety and exposure during installation, maintenance and repair.
The information sheets provided will list the advantages, limitations and common problems of each of the VMS treatments. These may be considerations such as installation uses typical maintenance equipment/practices or may require leave-out to meet AASHTO RDG and MASH compliance requirements. Common problems may note something like VMS is easily displaced by errant vehicles and maintenance equipment.
Guardrail – The guardrail category includes guardrail transitions and other related components. “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 101).
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”x8”x72” and the steel post is W6x8.5 or W6x9 and 72 inches long. The W-beam is typically 12-guage (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 Median). 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.
Support Posts and Poles – Includes 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 – A strip placed at the edge of a noise wall, roadside appurtenance, etc. that facilitates mowing.
Slope/Embankment – Designates areas where the roadside rises or falls from the roadway elevation. The degree of steepness is site-specific.