Limited-Access Arterial Plantings

Landscapes along limited-access arterial highways feature shade and evergreen trees, understory plantings, and turf grass to provide a green buffer for adjacent communities and enhance the natural environment. These areas are typically much larger and allow for a greater diversity of plants than is possible elsewhere. However, irrigation is rarely provided, and plants must tolerate other urban stresses such as wind and salt.

Limited-access arterial highways are high-speed roadways, such as expressways or parkways, with access ramps, no intersections with traffic control, and generally large areas for plantings. The most commonly used ground cover for limited-access arterial highways is turf grass. Arterial lawns are mowed about four times during the growing season. No fertilizers or pesticides are used, and there is never supplemental irrigation after establishment.
 

Plantings along an access ramp and bridge structure: Belt Parkway, Queens
New planting featuring various tree species: Brooklyn Queens Expressway, Brooklyn

Benefits

Review Benefits of Plantings in the ROW

  • Limited-access arterial ROWs often contain large contiguous areas suitable for re-forestation, providing some of the benefits of natural woodland, including corridors for wildlife
  • Opportunities for greater diversity in trees and other species and preservation of native species where existing conditions are not unduly disturbed
  • Summer cooling, wind reduction, buffering of negative traffic perceptions, glare reduction, and enhanced aesthetics provide a more pleasant experience for motorists
  • May provide moderate stormwater capture
     

Considerations

Review Key Considerations

  • Planting must comply with DOT design standards and guidelines and NYSDOT guidelines if located within areas under NYSDOT jurisdiction

Siting

  • Consider visibility in relation to the overall height of mature plantings, especially with Raised Plantings
  • Trees should not be planted closer than 20 feet apart to allow for mowing. Space should be provided for maintenance vehicles and crews
  • Plantings should not create hidden areas that facilitate illegal activities such as dumping or vandalism

Environmental

  • Soil can be highly variable in texture, pH, and depth; compaction is typical and can greatly suppress root growth as well as cause drainage problems
  • Plants must be able to tolerate various stresses such as reflected heat, salt, drought, wind, and competition from invasive plants
  • Plants known to be susceptible to insect or disease problems should not be used
  • The Port Authority of New York and New Jersey prohibits plants with fruit that attracts birds near the airports

Maintenance

  • Limited-access arterial highway landscapes typically receive limited maintenance; there is no weeding or invasive-species removal; maintenance typically consists of litter removal, lawn mowing, tree pruning for safety, and limited herbicide use along landscape edges
  • Any plantings not maintained by DOT or Parks will require a maintenance agreement
  • Consider DOT’s Adopt-a-Highway program for enhanced maintenance

Application

  • Any planting within along a Limited Access Arterial roadway; may include street trees, ornamental plantings, stormwater plantings, or other types of vegetation. Street trees should be planted wherever possible. Plantings are typically maintained by DOT or Parks.

Design

  • In-Ground Plantings are preferred. Raised Plantings may be considered where below-grade constraints prevent in-ground planting; design to the minimum height necessary to accommodate necessary soil depth and ensure positive drainage beneath the planted area is provided.

Safety and Clear Zones

  • Limited-access arterial highways without curbside safety barriers must maintain 30-feet clear zones (an area clear of fixed objects, such as trees, hazardous to vehicles involuntarily leaving the roadway at high speed) on either side. Access ramps must have clear zones measuring at least 15 feet on either side. All clear zones must be approved by DOT
  • A minimum of 10 feet behind any safety barrier should be clear of trees and other fixed objects

Planting

  • Review the Plant Finder for plants that perform well in the right-of-way. Plant selection must always be made based on site-specific conditions
  • Arterial landscapes are usually viewed by highway users at fast speeds; plant large swathes of fewer types of species
  • Large-growing shade trees should be spaced to promote maximum growth, typical form, and sturdy structure; interplant large trees with smaller understory trees and shrubs to increase the density of plantings
  • A good highway plant palette includes hardy species known to thrive and other plants for diversity and interest; review Key Considerations: Plant Selection
  • Incorporate Planted Stormwater Management Practices where appropriate. Generally, restrictions on space do not apply, so such infrastructure can be much larger
  • Consider use of a pollinator-friendly native plant seed mix combining grasses and forbs, particularly on slopes exceeding 3:1 where mowing may be difficult

Turf Management

  • Use low-mow fescues or similar turf grass species to reduce mowing frequency where practical
  • Ensure turf species are well-suited to the site to maximize vigor and density for erosion control and quick repair of physical damage

Maintenance

  • Asphalt mow strips, or similar treatments, are required around and under objects that mowers cannot pass over
  • Mulch around trees, without covering the root flare or trunk, to reduce damage from tractor mowers and greatly improve tree health; a 3-feet minimum diameter mulch bed is required around new trees and a minimum 5-feet diameter is required around existing trees

 

Trees on the side of a highway

Various tree species: Hutchinson River Parkway, Bronx

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