Trees in Relation to Street and Highway Design

Two types of approaches are recognized: the ones that would typically be used in suburban areas and others that would primarily be used in retrofitting or creating new streets in older urban areas.

Suburban Areas
The following have good elements for tree planting and pedestrian safety and can be models for future improvements.

Neighborhood streets: Three solutions to conserve or provide more trees with new subdivisions.

• Asheville, North Carolina: Separated sidewalks with provisions to save existing trees. In very low-density areas, a sidewalk on one side of the street could serve a neighborhood.
• Farragut: Some streets are designed in a more traditional fashion, including separated sidewalks and planting wells.
• Sequoyah Hills (also Lindberg Forest): Narrow local roads in very low-density situations can save trees. A provision for sidewalk or pathway system, such as that used in Norris, would improve the design.

Thoroughfares: There are several prototypes that offer more opportunities to plant trees, provide a safer and more comfortable pedestrian environment and offer a more attractive means of access to adjoining land use than the 5-lane arterial that has been routinely used in road building.

• Maryville’s Lamar Alexander Parkway: This arterial road includes landscaped medians, separated sidewalks, and in many sections, an attractive border of large deciduous trees.
• Knoxville’s Parkside Drive: Its 16-foot wide medians (planted with small trees), tapered turning lanes, and maples along the edge of its right-of-way are attractive features. Separated sidewalks would improve the design.
• Madison, Wisconsin: This city, long recognized for its beautiful streets and parkways, continues to create arterial roads that have landscaped medians and separated sidewalks and are designed to foster a mix of land uses including a pleasant setting for higher density residential development.
• Gleason Road (extension to the east): This short extension with its landscaped medians, sidewalks and turn lanes is a good model for situations where adjoining land uses generate moderate levels of traffic and good turning movements are needed.

Urban Areas
Other prototypes, which are particularly useful for road improvements in older parts of Knoxville or when new subdivisions are created in respect to the Traditional Neighborhood Development or Town Center sections of Knoxville’s zoning ordinance are outlined below. The design features are based upon guidelines that are recognized by the North Carolina Department of Transportation

Residential Alleys

Basic Considerations: The alleys in older residential areas were often built in horse and buggy days. Their rights-of–way and pavement widths (if paved) are narrow. Furthermore, the lack of setback standards for alley-oriented garages results in awkward access to garages or, by default, no automobile parking off of alleys. As a consequence, vehicles are often parked on planting strips and sidewalks or in front yards, negatively affecting a neighborhood’s streetscape. New or reconstructed alleys should be based on the following guidelines.

Features:

• Right-of-way: 20 feet (minimum)
• Utilities, either above or underground, may be located in alleyways to provide service connections to rear elevations
• Width: 12 feet (minimum)
• Additional pavement at alleyway intersections is necessary to facilitate turns.
• Larger trees to side of garages; smaller trees could be planted toward outside portion of the right-of-way where they would not interfere with access to garages

Lane

Basic Considerations:
Relatively short streets that provide access to residences. Some of Knoxville’s grid streets that do not have curbs and sidewalks are potential candidates.

Features:

• Street width: 18 to 22 feet with curb and gutter and informal parking designated on street
• Planting strips: 6 foot minimum
• Sidewalks: 5 feet on at least one side
• Design speed: 20 mph
• Posted speed: 20 mph
• Requires a 40 to 44 feet right-of-way
• Drainage: curb and gutter
• Generally two to six blocks long

Street

Basic considerations:
The basic residential street; a few of early Knoxville streets are similar as are the improvements in the Mechanicsville Commons

Features:

• Street width: 28 feet with curb and gutter and informal parking
• Planting strips: 6 foot minimum
• Sidewalks: 5 feet on each side
• Design speed: 20 mph
• Posted speed: 20 mph
• Requires a 50 feet right-of-way
• Drainage: curb and gutter
• Generally two to six blocks long

Avenue

Basic considerations:
Avenues are medium speed connectors between a core area such as downtown and neighborhoods. Adjoining land uses can include a mix of residential, office and commercial uses, including a vertical mix of those uses within a building.

Features:

• Street width: 26 feet on both sides of median with on-street parking; 18 feet if no parking or curb and gutter
• Median width: 18 feet (minimum)
• Travel lanes: 11 to 12 feet
• Maximum: 2 travel lanes
• Bike lanes and planting strips: 6 feet
• Sidewalks: 5 to 8 feet depending upon intensity of adjoining land use
• Design speed: 30 mph (maximum)
• Posted speed: 25-30 mph
• Right-of-way depends upon width of design features
• Drainage: curb and gutter

Boulevard

Basic considerations:
Can be used to provide connections through parts of the city. Adjoining land uses can include a variety of uses, including various residential types, commercial, office, and institutional uses.

Features:

• Lanes: 11 feet with striped parking and bike lanes
• Maximum of 4 travel lanes
• Median width: 20 feet is recommended
• Planting strips: 6 to 11 feet
• Sidewalks: 5 to 8 feet, depending upon intensity of adjoining land use
• Design speed: 40 mph (maximum)
• Posted speed: 30-35 mph
• Right-of-way: depends upon the width of design features
• Drainage: curb and gutter