CHAPTER 1
Introduction

1.1 Roadside Vegetation Asset Management

This guide describes how state departments of transportation (DOTs) can promote and implement roadside vegetation asset management (RVAM). The guide offers suggestions, including support for promoting and updating RVAM plans and information on tools and technology that can serve state DOTs during RVAM tasks. To help agencies seeking to implement or update RVAM plans, this guide describes issues, suggestions, and lessons learned by state DOTs that have implemented roadside vegetation asset management.

Vegetation and roadside safety features are critical elements of state DOT rights-of-way (ROW). These assets help stabilize soil, prevent erosion, and sequester carbon, thereby increasing the resiliency of the roadside. Additionally, vegetation and roadside safety features provide habitat for pollinators and other wildlife, wildlife crossings, a calming effect on the traveling public, safety barriers, and visual barriers, among other benefits. When vegetation fails, structural elements of the road and surrounding area can be negatively affected.

NCHRP Project 14-47, “Tools and Technology for Roadside Landscape Asset Management,” was created to find a solution to integrate Roadside Vegetation Asset Management (RVAM) into state Department of Transportation (DOT) asset and performance-based management systems within the proper context. In reviewing comments and responses to the survey questions, the authors found that state DOT staff had difficulty with the definition of Roadside Landscape Asset Management (RLAM) due to the term “landscape.” The term “landscape” was being used by respondents to describe formal vegetation plantings. Therefore, “landscape” was replaced with “vegetation,” and the term “RVAM” was adopted for this project.

A definition of RVAM was developed during the project to facilitate understanding and implementation: Roadside Vegetation Asset Management is the systematic process of developing, operating, maintaining, and measuring vegetation assetsʼ and roadside safety featuresʼ state of repair, as well as planning for, upgrading, and disposing of vegetation assets and roadside safety features in the most cost-effective manner. Roadside vegetation assets were defined within the project as visible features along the right-of-way that include vegetation and roadside safety features (e.g., trees, turfgrass, and native plantings, as well as guardrails, slopes, and sound walls) that affect vegetation maintenance access. State DOTs can use tools and technology to achieve the goals of RVAM plans by providing field staff with access to equipment and geospatial records and by providing management staff with equipment and timekeeping reports for planning workloads and tracking work progression.

1.2 Importance of Roadside Vegetation Asset Management to DOTs

Roadside vegetation assets help support the foundation on which structural assets are built. When vegetation fails, there can be significant effects (e.g., landslides and erosion) on the environment around it. Ensuring that vegetation surrounding roadside safety features is healthy and properly maintained can increase the visibility, lifespan, and effectiveness of these assets and can reduce structural failure where these assets break down or become ineffective. For example, when vegetation assets are not effectively maintained, vegetation near guardrails may grow unimpeded and obscure the guardrails. Such visual obstruction increases the likelihood of minor vehicular collisions with the guardrails. Such collisions can then reduce the guardrailsʼ structural integrity and increase the likelihood of failure in the event of a more severe accident. Well-maintained vegetation assets can help reduce maintenance costs for multiple structural assets, including roadside safety features.

During the case studies, RVAM costs were found to be associated primarily with staff salaries rather than equipment or material expenses. When evaluating staff and equipment costs, vegetation assets cost less per square foot to maintain than many structural assets, despite being more numerous along the right-of-way. Vegetation assets can affect the integrity of structural assets and decrease their lifespans by decreasing visibility along the right-of-way (which increases the likelihood of accidents) or by expanding the size and depth of cracks in structural assets (due to a vegetation assetʼs root system). Structural asset failure often requires costly repairs or even asset replacement. Maintaining vegetation assets to increase the lifespan of structural assets can help reduce costs overall.

In addition, vegetation provides benefits such as carbon sequestration, pollinator habitat, aesthetic appeal, shade that reduces the urban heat island effect caused by pavement solar reflection, water filtration, stormwater management, wildfire resilience through the removal/control of fire-prone vegetative species, soil stabilization, and many other services. These effects can be seen off the right-of-way in the reduced risk of landslides, fire, and flooding; increased use of the right-of-way for evacuation; and the connection of wildlife areas for conservation. Vegetation provides ecosystem services that ultimately save state DOTs money when functioning correctly and when recommended management practices are followed. Certain RVAM practices can also provide opportunities for state DOTs to participate in agreements [e.g., the Monarch Candidate Conservation Agreement with Assurances (Monarch CCAA)], and given the limited maintenance needs of many native groundcover species, these practices can reduce department maintenance costs (Davey Resource Group 2023). The research team found that programs like those that promote pollinator habitat may be able to provide short-term funding to support efforts to establish habitats and address related maintenance needs.

Vegetation planted for functional, rather than aesthetic, purposes falls between the structural and vegetation asset classes. Functional vegetation requires management like that of other vegetation assets, but the function is like that of structural assets. An example of this is “living” snow fences. These assets, while made of vegetation, serve the same purpose as structural snow fences—snowdrift control. Given the similarities of functional vegetation plantings and vegetation assets, functional vegetation plantings are included within vegetation assets, unless otherwise noted.

Vegetation plantings can serve any of the following functions:

• Visual screens (for unsightly areas or to reduce headlight glare)
• Visual buffers
• Noise-reduction barriers
• Impact attenuators (depending on location and type of plant)
• Delineators

• Snowdrift control
• Erosion control
• Improvement of air quality
• Improvement of motorist temperament and reduction of vehicle speeds

1.3 Differences Between Roadside Vegetation Asset Management and Hardscape Asset Management

Structural and vegetation assets require different maintenance strategies that may not be able to be performed using the same tools and technology. This is because vegetation assets change regularly throughout the year and structural assets change only because of deterioration and direct damage. The timing and amount of maintenance varies between the two asset classes as well. Vegetation assets require regularly scheduled maintenance, while hardscape assets may only need maintenance on certain sections once per year or less, depending on the state DOTʼs goals, the asset, and its location along the right-of-way. For example, in some climates, state DOTs must conduct vegetation asset management tasks—such as mowing in the clear zone—multiple times per year, while in other ecosystems, mowing may only need to occur every few years. These differences can, in part, contribute to differences in funding data collection, with low-cost, high-quantity assets (e.g., vegetation) receiving less focus on data collection than high-cost, low-quantity assets (e.g., bridges) (Rasdorf et al. 2009).

Hiring practices in most states prioritize equipment operators who can perform maintenance tasks over staff trained in vegetation management. As noted in the surveys, most state DOT staff have insufficient training on invasive plant species, hazard tree identification, and invasive pest identification, making it more difficult for them to determine when maintenance is needed. In contrast, state DOT staff who assess structural assets are provided with ample training to identify repair needs.

Many state DOTs do not provide staff or contractors with dates for completing specific vegetation management tasks. This results in state DOTs prioritizing vegetation management only after completing all the work that has set deadlines. Given the low prioritization of scheduling vegetation management, staff can have difficulty completing work during seasonally appropriate windows (some of which are regulated by the U.S. Fish and Wildlife Service [USFWS] such as those for threatened and endangered species). The lack of scheduling windows results partly from giving all the vegetation management work the same priorities within vegetation management guidelines. Effective vegetation management strategies take the broader context of local ecosystems into account. Work tasks are partly determined by functional ecosystem needs (e.g., plant lifecycles) and legal restrictions (e.g., bat hibernation windows, ground-nesting bird windows, and targeting of invasive species before they go to seed).

Vegetation management work completed throughout the growing season to maintain safety is less noticeable to the public than a repaving event that disturbs traffic flow and appreciably disrupts commutes. However, when vegetation fails to perform its role in preventing erosion, landslides, and rockslides, or obscures lines of sight and safety features, this vegetation failure causes an immediate safety threat that must be mediated by the state DOT. When RVAM assets are effectively maintained, the roadside is more resilient to the effects of issues such as changes in weather patterns, wildfire, and sinkholes/land erosion. Tools and technology can help state DOTs identify and mitigate these issues before safety incidents occur.

Advanced tools and technology that can detect maintenance needs are being used for structural assets (e.g., bridges). Because vegetation assets change in shape and coloration throughout their lifecycles, the types of asset tracking and monitoring software and hardware differ between vegetative and structural assets. Some state DOTs prefer to purchase dual-purpose equipment,

tools, and technology that can manage multiple asset types. Although this approach allows state DOTs to use such systems throughout the year, instead of solely during vegetationʼs seasonal maintenance windows, the limited capacity of many tools and technology to work with both vegetation assets and structural assets can prevent their dual use. Several technology companies are investigating ways for their products to identify vegetation asset maintenance needs (Verbree, Zlatanova, and Smit 2004, Pusztai 2021, Joshi and Witharana 2022, Li et al. 2019, Creusen and Hazelhoff 2011). The research team met with vendors who specialize in mapping state DOT assets. Most of these vendors focus on hardscape and structural assets and have not considered using the technology for vegetation asset management. Several vendors acknowledged it would be possible to modify their tools to make them suitable for vegetation management, but they had not explored this because they had not been contacted to provide such services. As companies make technological advancements, state DOT maintenance operations may want to communicate that there is a demand for these technologies to apply to vegetation.

1.4 Roadside Vegetation Asset Types and Definitions

State DOTs categorize roadside vegetation assets in existing inventory systems as either “roadside safety features” or “vegetation.” These include hardscape assets (e.g., culverts, guardrails, and sound walls) and functional vegetative features (e.g., living snow fences and windbreaks). State DOT staff survey structural assets to identify issues (e.g., cracks or breaks). They monitor vegetation by looking for erosion, invasive plant species, growth obscuring sight distance and access to structural assets, and tree failures that can be safety threats to the traveling public. Vegetation is monitored to determine when individual vegetation assets need to be mowed, replaced, or removed from the right-of-way. Because each state DOT uses different language to describe vegetation assets and includes different safety features in their RVAM plan, the need for a list of RVAM terms for use across multiple state DOTs became apparent. This list was created as part of the research (and is included herein as Appendix A). Many structural assets that provide roadside safety are included because vegetation must be maintained around these assets to ensure compliance and effectiveness (e.g., clearing vegetation around guardrails). Roadside safety features include snow fences, sound walls, guardrails, and cable rails. Several of the roadside safety features include a vegetation option if a state DOT prefers to use a nonstructural approach for safety.

Roadside vegetation safety features reduce the need for state DOTs to buy and maintain more expensive structural assets. Roadside vegetation safety features include assets grown to replace structural assets (e.g., living snow fences and windbreaks) and erosion control measures (e.g., tree plantings). For example, structural snow fences can be made of plastic, wood, or metal. The snow fences can be removed during the spring to improve line of sight, to reduce damage to these seasonal assets from mowers and other equipment, or to make the private land available for farming or alternate uses. A living snow fence made of herbaceous plants can be mowed as needed and regrown in preparation for the following winter season. Tree lines and shrub lines that create living snow fences do not typically require as much maintenance as structural items.

1.5 Current State of Roadside Vegetation Asset Integration

Only a few state DOTs have begun integrating roadside vegetation asset management into inventory systems used for structural assets. The use of emerging technology (e.g., Building Information Modeling [BIM] and digital twins, as described in the California Department of Transportation [Caltrans] case study [Appendix B]) will allow state DOTs to identify all assets along the right-of-way. All states that served as case studies use mapping technology to identify hazardous trees, irrigated landscaped areas, and other vegetation assets to better plan roadside

vegetation asset management. Some state DOTs [e.g., the Washington State Department of Transportation (WSDOT) and the Ohio Department of Transportation (ODOT)] have staff map both vegetation and structural assets on the same tablet and application. Other state DOTs (e.g., the Tennessee Department of Transportation [TDOT]) contract out mapping services as needed. To do this efficiently, the systems often require similar terminology for both structural and vegetation assets.

Incorporating safety features into structural inventory systems and state transportation asset management plans (TAMPs) can be most readily accomplished with roadside safety features (e.g., culverts). These safety features are like other structural assets already inventoried and included in state TAMPs in terms of the yearly amount of available funding and maintenance needs.

Although some states have fully integrated roadside vegetation asset management into inventory systems by developing new inventory systems from the ground up, others have used existing systems developed for assets already included in the TAMP. For example, WSDOT developed the Highway Activity Tracking System (HATS) to track all assets within the maintenance division. ODOT developed the Bi-Weekly Collection App to track most assets within the maintenance division. Caltrans developed an application to track and determine conditions for landscaped areas within the state DOT right-of-way by modifying a similar system initially designed for culverts. Caltrans decided to base the vegetation management application on the culvert application rather than another application because of the similarities of condition ratings required for vegetation management.

Successful integration within a state DOT depends on support from the Information Technology (IT) department and upper management. The IT department may need to update or create programs to enable the integration of tools and technology for vegetation monitoring and maintenance records. Upper management may need to (1) approve funding to purchase or develop the tools and technology and (2) approve the resulting staff training to ensure staff can use the new tools and technology.

The surveys and case studies made clear that those states that can use or adapt existing systems will more easily incorporate RVAM tasks into their TAMP or the guidelines that determine the work to be completed each year.