Right of Way Vegetation Management

Right of Way Vegetation Management

Rights-of-way may be found everywhere and are placed in every type of terrain, soil, climate, vegetation complex and land-use area. Vegetation management on rights-of-way is desirable and necessary for a number of reasons.  It is important to maintain a safe & clear sight distances, to clear signs and fixtures of vegetation for visibility and functionality, to provide adequate drainage in roadway ditches, soil erosion control, to reduce fire hazard and provide dust drift control. It is also necessary to protect the roadway surface from vegetation encroachment and to maintain drainage.Rights-of-way generally must be kept free of large brush or trees, that is, maintained in an early stage of plant community succession which means that vegetation must be continually managed. The type of vegetation management necessary will depend on the function of the right-of-way. 
Safety is the main reason of for Vegetation Control. Trees close to the road can present a fixed object hazard. Grass, weeds, brush and tree limbs can obscure or limit a driver’s view of traffic control devices, approaching vehicles, wildlife and livestock, and pedestrians and bicycles. Controlling vegetation helps reduce crashes and injuries. The main goals of vegetation control include:
  • Keeping signs visible to drivers.
  • Keeping road users (vehicles, bicycles and pedestrians) visible to drivers.
  • Improving visibility of livestock and wildlife near the road.
  • Helping pedestrians and bicyclists see motor vehicles.
  • Keeping sidewalks and pedestrian paths clear and free from overhanging vegetation.
  • Removing trees close to the roadway which could result in a severe crash if hit.
  • Improving winter road maintenance in icy areas.
  • Helping drainage systems function as designed.
  • Preserving pavements through daylighting and root system control.
  • Controlling noxious weeds in accordance with local laws and ordinances.
This handout describes conditions commonly found on streets and how you can identify potential hazards caused by vegetation.

Roadway Vegetation Management
Roadway vegetation management programs define the best maintenance practices for each location. An integrated roadside vegetation management program consists of eliminating or controlling vegetation through a variety of strategies including mowing, brush cutting (mechanical and hand), use of herbicides, grazing of livestock, cultivating desirable vegetation, and re-vegetation.
One useful way to look at how and why vegetation control is needed for safety is to think in terms of Roadside Management Zones. 

 ROW Drawing1
                     ROW Line         Zone 3   Zone 2             Zone 1                       Zone 2     Zone 3      ROW Line

                                                  FUNCTIONAL ZONE OBJECTIVES

 ZONE 1: Vegetation Free Zone            ZONE 2: Operational Zone                ZONE 3: Transition Zone
(width as necessary to meet operational Zone)   (from Zone 1 to meet operational needs)     (from Zone 2 to ROW Line)
Provide for surface drainage                                   Maintain a hazard free vehicle                         Blend and/or screen adjacent
Prevent pavement breakup                                     recovery area                                                       surroundings
Provide for visibility and maintenance of              Provide sight distance for passing and            Control weeds
roadside hardware                                                    stopping                                                                Remove danger trees
Provide sight distance at intersections           Manage trees to reduce 
                                                                                       Maintain hydraulic capacity of ditches            shading in areas prone to 
                                                                                                                                                                      roadway icing 
Keeping Traffic Control Devices Visible
Drivers need an unobstructed line of sight to any roadside signs or roadway hazards far enough ahead to allow them to react safely to each situation. Right-of-way control signs (STOP and YIELD signs) are most critical. Tree branches or brush in front of a sign can hide it from view of motorists. Often, a small branch from an overhanging tree or bush near the sign is all that needs to be trimmed. If vegetation along the ditch or shoulder blocks a driver’s view of a sign, then cut enough to allow a driver sufficient time to see the sign and respond to its message. 

Tall grass, weeds and brush in the shoulder, ditch and backslope areas of a roadside can create problems. Low fixed object hazards such as culvert headwalls, drainage inlets, guardrail ends and any object markers in front of them can be hidden by tall grass, as can wildlife and livestock. High grass can also obscure the shoulder. Shoulder and roadside maintenance such as grading or mowing should be done to define the edge of shoulder and ditch so that motorists can see the shape, condition, and limits of the roadside. 
Stopping Sight Distances on Curves
On horizontal curves, vegetation on the inside of the curve may restrict the driver’s line of sight. Roads are safer when drivers can see as far ahead as it takes to stop their vehicles. The distance it takes to notice a problem, realize a stop is necessary and come to a complete stop is called stopping sight distance.
Stopping sight distance is important along all roadways. Where vegetation is close to the road, special attention needs to be given to stopping sight distance on the inside of curves. These areas should be checked when vegetation growth is at its peak to make sure stopping sight distances are adequate. Sight distance is measured along the travel path of vehicles. The conventional procedure used in measuring stopping sight distance assumes that a driver’s eye is 42 inches above the road surface. The procedure also assumes that a driver must be able to detect an object that reaches 24 inches above the road surface on the road ahead.
On the inside of horizontal curves, vegetation growth close to the edge of pavement can block a driver’s view of motor vehicles (in the same or opposite direction), bicycles and pedestrians. Maintaining roadsides so headlights and taillights can be seen around the inside of horizontal curves can increase the horizontal sight distance available. 

ROW5Drainage: Weeds, turf and sod can interfere with roadside drainage. A high shoulder creates a secondary ditch and damages the pavement. Water on the pavement due to high shoulders creates safety problems, including hydroplaning and isolated icy conditions during the winter. Grading may be necessary to make sure the shoulder continues the road crown smoothly.
ROW6Side Road Visibility: Roadway intersections increase the chances of vehicle crashes. Safe and efficient vehicle movement through an intersection requires good visibility. As drivers approach an intersection, they need to check each quadrant of the intersection for the presence of entering vehicles. Similarly, drivers pulling out from a STOP sign need a clear view of oncoming traffic. A clear vision triangle at each corner of an intersection helps drivers avoid problems.
ROW7Roadside Trees: One of the most common causes of fatal and serious injury crashes on rural roads involves vehicles leaving the road and striking a tree. The concept of a clear zone, an area adjacent to the traveled way in which slope, surface and an absence of fixed objects can permit recovery of a vehicle that leaves the roadway, is important to providing a safe roadside.

Trees are potential hazards because of their size and location with respect to vehicle traffic. Trees larger than 4 inches in diameter can be a hazard to a vehicle. The closer trees are to the travel lane, the more likely a vehicle is to strike them. Isolated trees provide a better opportunity for removal compared to forest conditions where removal involves significant cost. Recognize the sensitivity of removing individual trees.

Removal should be based on potential crash frequency and severity. First priority should be on removing trees closest to the road. Trees in critical locations such as curves and intersections should be considered for removal. Trees that have been struck deserve additional attention. Cut trees close enough to the ground so that no stump remains to be a fixed object or snagging hazard. Trees of any size growing on a slope should be cut flush with the ground. Generally, any stump higher than 4 inches above the surrounding ground can cause snagging. Snagging occurs when a vehicle undercarriage catches on a stump or other object.

Note that while trees close to the road should be removed for safety, those that also provide shade for waterways should be mitigated to a safer location because water temperature is crucial to fish habitat.  Potentially hazardous trees outside the right-of-way should be referred to property owners for removal unless an emergency situation exists. 

Pedestrian Paths: Today, there is increased emphasis on walking for exercise and transportation. It is important to pay attention to the effects of vegetation on pedestrian safety and walkway accessibility. Just like a roadway corridor, a sidewalk corridor is made up of different zones as shown on the figure to the right.
 ROW Drawing2
Zones making up a sidewalk corridor.

The pedestrian zone is specifically reserved for walking. The zone must be completely free of overhanging and protruding obstacles, including vegetation. ROW8

Tree branches that protrude into the sidewalk corridor must be cut or trimmed.

Another sidewalk safety concern that can be caused by vegetation is “changes in level”. A change in level is a vertical elevation difference between adjacent surfaces. ROW9
They can be tripping hazards for pedestrians and can make a walkway inaccessible to wheelchair users. One of the most common causes of a change in level in sidewalks are concrete slabs heaved up by tree roots. While street trees have a number of advantages, the type of tree should be selected carefully to minimize the root problem. Use of root guards should be considered in some cases.
Intersection Sight Distance
Another important sight distance requirement that can be affected by vegetation is intersection sight distance.   Drivers approaching an intersection need a clear line of sight to the intersection and along the crossroads early enough to see any conflicting vehicles, bicyclists and pedestrians to avoid a collision.  Together these sight lines provide a sight triangle.  These sight triangles can be limited by the presence of horizontal and/or vertical curves, buildings and other physical objects, and vegetation.  Providing adequate clear sight triangles is critical for safety of all road users, so you want to make sure that vegetation overgrowth is not limiting the sight distance at intersections.

If you find that vegetation is limiting the corner sight distance, then you should cut it back if it is within the public right-of-way lines. Usually, you are not permitted to work outside of right-of-way lines.  

Our City has an ordinance regarding a sight distance easement.  It states as follows:
12.12.020 Trees over sidewalks and streets.
A.    No branch of any tree extending over any sidewalk or street in the city shall be less than eight feet in the clear above such sidewalk.

B.    It is the duty of any owner or claimant of any tree with branches extending over any sidewalk or street in the city to remove the branches of any such tree to a height of not less than eight feet above the sidewalk or street thereunder.

C.    If any owner or claimant of any tree extending over the sidewalk or street in the city fails, refuses or neglects to remove, and keep removed, the branches thereof to a height of not less than eight feet from the sidewalk or street thereunder, it shall be the duty of the superintendent of streets or the chief of police to notify the owner or claimant of any tree maintained in violation of this section to remove forthwith and without delay all overhanging branches thereof to a height of not less than eight feet, as provided in this section.

D.    Unless within ten days from the date of notification by the superintendent of streets or the chief of police of the city, the owner or claimant of any tree with overhanging branches maintained in violation of this chapter removes such branches to a height of not less than eight feet in the clear, the superintendent of streets shall remove or cause them to be removed without further notice or demand. (Ord. 216 §§1--4, 1927)

This ordinance gives us the authority to ask the property owner to trim back any trees or shrubs blocking the corner sight triangle or to cut them.  No shrubs or plants within the corner sight triangle should be allowed to grow more than 3 feet high. If notice is provided and homeowners do not respond in a reasonable time, our city will have the power to remove the designated vegetation at property owner’s expense.

Most private property owners are willing to cooperate in improving traffic safety at intersection.  They should be required to keep all bushes and shrubs at a height of 3 feet or lower and to trim all trees and hanging branches to a minimum height of 7 feet. 

Federal Highway Administration, Roadside Vegetation Management
International Society of arboriculture
National Roadside Vegetation Management Association www.nrvma.org