Landscape Design Considerations
Before hitting the drawing board to create a roadside landscape design, you need to do a quick check of seven things. Block out zones for setbacks, vertical clearances, overly steep slopes, clear sight lines, sign visibility, guard rails, and utility easements to keep your landscape design free of safety conflicts. By checking these items initially, you can map out the basic configuration of use zones and develop the structural framework from which your design can be based. Those zones, drawn on a base map, develop site development shapes, and a clear design concept calls out to you.
Consider the following items your first priority:
• Setbacks and the Clear Zone
Keep any tree you propose on public rights of way well beyond the required safety clear zone. Trees in the clear zone create a fixed object that might be hit by an errant driver that runs off the road. This gives the driver an opportunity to recover and get back on the road without injury or damage to the vehicle. This may seem elemental to seasoned designers, but I’ve seen a surprising number of plans submitted for review without adequate setbacks.
• Tree Canopy Clearance
Leave an adequate vertical space open along the travel way to avoid overhanging branches in the road. Limbs can slap against panel trucks driving near the edge and remove rear view mirrors. Twelve feet of vertical clearance is a good minimum. Trees overhang pedestrian corridors, too. The limbs over sidewalks need to be higher than a pro basketball player.
• Slope Steepness
Plant material can barely establish and grow on slopes steeper than 3:1, and will be unstable on slopes steeper than 2:1. Steep hillsides are dangerous to mow and cannot provide recovery space for errant cars. A design can look gorgeous to a bird flying overhead, but be impractical for people, plants, and storm drainage. Address slope issues before choosing plant material.
• Sight Lines
Drivers need to be able to see oncoming traffic when they attempt to turn into or cross over public roadways. It is the designer’s responsibility to keep sight lines open for drivers and pedestrians. Anything over thirty inches tall can block the view, and you cannot count on public funds to provide for constant pruning maintenance. Choose small plants for sight triangles.
Keep view zones for directional and advertising signs free of vegetation that will grow to obscure the signs. If you don’t, there is a chance your newly planted landscape will mysteriously disappear, be damaged, or die, especially during the weekend when transportation workers are not monitoring the roadsides.
As tempting as it may be to soften guardrails with picturesque vines, the structures must be kept visible at all times. Softening guardrails, utility poles, and rip rap areas is not an option. Infrastructure and safety trump romanticism every time.
Utility companies will remove any plants within their easements that threaten their lines from working properly, and the result is not always pretty. It’s easy to overlook the potential conflict when drawing landscape plans, and easy to push the limits for the sake of a design, but don’t. Keep a generous buffer between trees and the outside phase of any utility line. Think about potential disruption of underground utilities, too, and keep large vegetation out of easement areas.
It may seem like avoiding safety conflicts and being practical leaves no room for landscape enhancements! All great landscapes have challenges that must be overcome. Angst is where your creativity and innovation are sparked. Elevated design in the real world transforms issues into defining inspiration. Use these challenges to build your landscape design skills.
Rather than argue for variances and political favors to push forward with your landscape plans as is, consider how your design might benefit from innovative revision. Easy designs result in sub-standard outdoor experiences. Real satisfaction in your work comes from constructing a legacy for others to safely enjoy long-term.
You can find more information about trees in The Advanced Guide to Roadside Design: How to Create Successful Public Landscape Projects, part of The Advanced Guide series.