Chapter 5 - Roadside Safety and Horizontal Clearance

5.8. Horizontal Clearances to Trees and Shrubs

Guidance on horizontal clearances with regard to trees and shrubs is provided from the GDOT Office of Maintenance, which also includes approvals through the Office of Traffic Safety and Design. Additional guidance is provided by the Office of Planning through the GDOT Pedestrian and Streetscape Guide.

Utilities and intersection sight distance requirements may affect the location and diameter size of proposed trees in the horizontal clearances and clear zone. Clear zone requirements can be found in the AASHTO Roadside Design Guide or in Chapter 4 of the current GDOT Regulations for Driveway and Encroachment Control.

The design speed shall be used to determine horizontal clearance criteria.

5.8.1. Rural Shoulders

On roadways with rural shoulders, trees and shrubs shall be located outside the clear zone.

5.8.2. Urban Shoulders

On roadways with urban shoulders with a posted design speed of greater than 45 mph, trees and shrubs shall be located outside of the clear zone. 

On roadways with urban shoulders with a posted design speed of 45 mph or less, refer to Table 5.3. for minimum horizontal clearances for trees and shrubs.

The designer should note that AASHTO Roadside Design Guide measurement of trees differs from that of landscape architects. The recommended point to measure a tree is 6 inches above the base of the tree. 

 

Table 5.3 Horizontal Clearances to Trees and Shrubs: Urban Shoulders
Posted / Design Speeds	Minimum Horizontal Clearance(1)
Tree Size(2)  < 4 inches
< 35 mph	4-ft.
40 to 45 mph	8-ft.
Tree Size(2)  > 4 inches
< 35 mph	8-ft.
< 35 mph (Commercial Area(3))	4-ft. 8-ft. in median
40 mph	10-ft. 16-ft. in median
45 mph	14-ft. 22-ft. in median
(1)From center of tree to face of curb   (2)Tree size is diameter of the tree at maturity, measured at 6-inches above the base of the tree.   (3)In a Central Business District and/or where commercial businesses are typically directly adjacent to the right-of-way.

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