Roadside Vegetation Management

Purpose of Cutting Trees and Shrubs 

Removing trees and other plants from within the right-of-way that interfere with the safe operation of the highway system is an important element of vegetation management. The reasons for cutting back plants or removing them entirely include: 

• Keeping the Recovery Area clear of fixed hazards

 • Maintaining sight distance at intersections, cross roads, and along curves

 • Removing vegetation that may obscure wildlife with the potential to cross the roadway and cause a collision
• Removing trees that may pose the threat of falling on the roadway under conditions of high winds or unstable soil
• Controlling invasive species • Removing trees and brush that obscure traffic signs, signals, right-of-way fence, and hazard markers

 • Preventing encroachment of plants into guardrails, distress lanes, drainage features, and shoulders 

• Removing vegetation prior to herbicide treatment

 • Removing and disposing of tumbleweeds and mustard weeds which have accumulated along fences, in cuts, and around drainage structures 

• Removing shrubs and groundcovers in over-planted landscape areas which need thinning for irrigation inspection and repair functions 

• Trimming trees in landscape areas to facilitate inspection and litter removal

 • Trimming shrubs and groundcovers in landscape areas to improve plant barrier density 

• Removing plants that are unhealthy or dead due to traffic damage, lightning, disease, or other problems

 • Removing weeds growing around landscape plantings of trees, shrubs, and groundcovers by hoeing, cutting, or string trimming

 • Preventing snow drifting and reducing ice on the roadway due to shading.

Purpose of Chipping 

Chipping is an economical method for disposing of roadside vegetation waste, including stems, limbs and trunks. Chipping allows for:

 • The recycling of vegetation material

 • Avoids the presence of unsightly debris in scenic or urban interface areas

 • Assists in retaining soil moisture

 • Enhances soil structure over time

 • Provides for erosion control 

Purpose of Herbicide Use 

Herbicide use is one of the primary methods for managing roadside vegetation, protecting roadway integrity, and improving motorist safety. Herbicide application is used in coordination with physical methods to control vegetation in the right of way and should be used as part of an integrated roadside vegetation maintenance program. Herbicides are used to: 

• Help maintain a clear recovery zone

 • Protect roadside infrastructure and pavement integrity 

• Control vegetation around roadside features such as guardrails, sign structures, delineators, gores, and headwalls to maintain visibility of hazard markers and reflectors

 • Preserve sight lines

 • Remove fire fuel accumulations

 • Selectively target vegetation that disrupts desirable vegetation communities

 • Remove invasive weeds

 • Inhibit/retard invasive seedling trees and shrubs 

Purpose of Mowing 

Because mowing can have opposite effects on plant growth depending on when and how it is done, it’s important to have the goal of the mowing in mind when planning when and how to do it. Mowing should be used selectively in roadside vegetation management for specific purposes, such as:

 • Improving horizontal sight distance at intersections and cross streets

 • Maintaining visibility of hazard markers, guardrails, and delineators

 • Controlling weeds and tree/brush seedlings, often coordinated with herbicide use

 • Reducing snowdrift

 • Reducing summer fire fuels 

• Reducing wildlife grazing

 • Increasing vegetative growth in native grass species to encourage seed production.

  Mowing can shorten the lifespan and health of plants depending on the timing, frequency and height at which plants are cut. Wait until late in the growing season and mow at a minimum height of six inches to in areas with desirable plants and grasses. Mowing causes grasses and broad-leaf plants to deplete energy stored in their root systems. If plants are mowed too often, too short (under six inches), or during the growing season before they transfer energy to the roots, they may not live to regrow the next year. Mowing later in the season also allows seeds to fall, leading to more new plants the next year. Mowing grasses during the active growing season can cause the next growth to be shorter and spread out more. The shorter the grass is mowed, the closer to the ground it will start branching off to grow, creating more spreading growth; Bermuda grass is a good example of this.