California Department of Transportation
 

Using the Vegetation Management Toolbox

Roadside vegetation controls like other design elements must be tailored to fit site-specific conditions. California’s diverse mix of landforms, climates, soils and other physical and cultural features ensure that no one single approach will be effective for vegetation control everywhere. The VMT is constructed to assist the designer in this decision process by providing a variety of treatment alternatives for each roadside design situation i.e. guardrails, side slopes, medians, etc. in the Treatment Categories section. In these lists the user can evaluate and compare the top five treatments for each situation. By clicking on the photo of the treatment the user can access detailed information including benefits/limitations, details/specifications and additional cost information in the Treatment Detail pages. Once the designer is familiar with the various treatments, or if they want information on the specifics, they can go directly to the page for that treatment.

Selecting the Appropriate Treatment

The Treatment section of the toolbox has been developed to aid designers in the selection process by providing the most current information available for vegetation control treatments based on applicability, cost, context sensitivity, constructability (difficulty of constructing), maintainability (ease repair, replacement and regular maintenance required) and life cycle value.

Areas of Use

Vegetation control treatments provide the designer with the opportunity to blend the functional performance of a treatment with community values, corridor concepts, man-made elements and existing natural materials. While community values and corridor aesthetics will vary from project to project, designers can get a sense of appropriate context sensitive design by performing a quick analysis of the highway environment or setting. The following five general land use categories have been developed to describe highway and adjacent land use:

 
Urban Setting Suburban Setting Transitional Setting Rural Setting Natural Setting
Highway Type Multi-lane Interchanges and grade separation Multi-lane Interchanges
and signals
Multi-lane to conventional Multi-lane to conventional Two lane conventional
Traffic Volume (ADT) High Med to High Medium Med to Low Low
Land Use High density concentrated residential, commercial and industrial Primarily residential with supporting commercial Large lot residential or scattered commercial, future development Agricultural, undeveloped or low density residential Very limited or no development - park land and open space

Estimated Cost and Life Cycle

A major consideration for any design element incorporated into a project are the initial capital investment and long-term maintenance and replacement costs. Many of the treatments recommended in the toolbox are emerging products in the transportation environment and subject to a wide range of bid prices for materials and installation. As these products become more widely used in the transportation environment the material costs should decrease while contractor productivity and knowledge increases leading to substantial cost reductions. It is the responsibility of the designer to recognize site constraints or opportunities that could influence bid prices within the range of estimated costs. Even prices for the installation of standard construction materials such as asphalt concrete or compacted road base can be higher than normal if the installation of the treatment occurs after other project features have been constructed.

In selecting a treatment cost alone should not be the determining factor. Several treatments are intended for temporary or short-term use where follow-up projects or additional phases are imminent. Initial costs should be weighed against the projected life cycle costs of the treatment as well as other factors such as public acceptance, maintainability, etc.

While cutting corners can reduce the initial capital cost of any treatment, under-designing inevitably reduces the long-term value the Department receives. A thin layer of asphalt without a proper base, or gravel mulch without an underlying geotextile barrier doesn't meet the major goals for the use of these treatments, which is to reduce Maintenance costs and worker exposure. Improperly designed treatments may actually make vegetation control more difficult by restricting access to the ground plane.

Benefits and Limitations

Within the Treatment Details are bulleted points that list the benefits and limitations for each treatment. Many benefits are obvious such as availability, contractor knowledge and the ability of Maintenance to perform repair. Less obvious benefits may include factors such as fit within the surrounding land development context, product peculiarities and flexibility. Limitations listed may include the effect of wind, soil moisture and hazardous materials on specific treatments. As feedback is gathered on the perfromance of each treatment, the treatment detail fact sheet will be updated to reflect this feedback.

Consultation

Finally, while the toolbox provides updated information and strategies for the designer, the most valuable tool in the selection of an appropriate treatment is early and frequent discussions with Maintenance, District Landscape Specialists, Traffic and Landscape Architecture. The technical input and site specific knowledge available from these consultations will reduce the variables and allow the designer to focus on the most suitable options that will satisfy the wide range of stakeholders.

Updated: Wednesday, May 24, 2012

 
 
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