Movement within the Landscape
Circulation dynamics help establish outdoor rooms and guide movement within the landscape.
Circulation provides logical movement from one outdoor room function to the next, but the most controlling facet of circulation is not function—it’s grade. The contours of a site dictate the flow of movement throughout the site. Luckily, grades can be changed, and you can force your will on the ground plane, but doing so usually threatens existing plant material and can be disrespectful of the sense of place each unique site possesses. Big box stores are the worst at site sensitivity. They abuse good circulation planning principles and, in the process, lose all sorts of opportunities to entice and welcome shoppers. The best advice I can give you about circulation is to avoid using big box techniques to develop the flow of people and vehicles on your site. Put some effort into working with the natural contours.
Don’t ignore circulation needs. A good landscape design starts with good circulation planning! Landscapes involve movement. It is important to visualize how each site user will be thinking to help them experience and benefit from the site visit. Do some role-playing.
Learn the minimum standards for widths, radii, heights, and slopes for the people, equipment, and vehicles that will be using the site. Then, be generous! Go beyond the minimums, for goodness sake, and make passage from place to place pleasant, rather than challenging. Add wide traffic separators and use them for planting opportunities. Good designers don’t plan for minimum standards of quality. They use their creative intellect to make special landscapes that just happen to comply with standards.
Learn the minimum criteria for paving stability and safety. Learn what reinforcement might be needed to keep the pavement strong. The subbase needs to meet standards, too. Compacted soils need to support the weight of the traffic and pavement above. Paving materials need to withstand the elements of weather and sun, and they need to be reinforced sometimes to handle firetrucks and oversized truck loads. It’s surprising how strong paving for vehicular areas need to be. For example, you might think nothing could be stronger than a brick. A beautiful, solid, brick basket-weave will flake away quickly under car tires. Thin asphalt will bend and distort under truck traffic. Concrete will crack and fail without the proper jointing and air-void ratios.
There are thousands of ASTM construction standards for everything you can imagine, and there are actual people (not robots) that make a living keeping current with the precise details of their industry’s latest requirements. It is daunting, and kind of tedious for normal people to research these standards. Make sure the pavement you design meets all the safety and material and quality and construction standards. If you are in design school, don’t leave before getting this information for your specialty from your professors. Pay attention when you are being taught this. After graduation, it will cost a premium for publications that provide it, but as a student, you are allowed significant discounts. The information is important, and worth the cost.
The transition from the edge of any circulation path and the rest of the landscape is an important visual statement opportunity. Use this changeover point to add flare to the function to the route. Edging can add clarity to the ground plane and provide visual cues to keep people on the right path. Rumble strips and exciting textural treatments provide warning strips that can prevent injuries.
Treat the grade carefully at the point where the pavement edging ends, avoiding dangerous drop-offs or tripping hazards for at least five feet beyond the path on either side. For steep grade changes, you will need to provide short, 1:12 ramps with flat, safety landings every twenty or thirty feet to prevent wheel chair acceleration.
Try to locate your paths to protect existing trees, but don’t let shrubs and herbaceous plant material, don’t allow the existing vegetation to dictate the circulation configuration. Small plants can always be moved. Also, it doesn’t hurt to take down fast-growing, weed trees. Be ruthless. Get rid of any tree that might be damaged significantly by your grading work. You can always plant more trees after everything is constructed. It is important to respect healthy, high quality tree specimens, though. Work your circulation plans around the drip line of special trees.
The type of expected traffic will determine the materials you choose for paving. The smoother and flatter the surface, the more easy it is to maneuver on the surface. However, perfectly smooth surfaces can be slick and dangerous. You need to add an element of friction to any sidewalk or pedestrian plaza to make it walkable. Texture is added with broom bristles or forms.
Sleeves, to provide later installation of utility and water lines, need to be strong enough to handle heavy traffic where vehicles will be cross. Use schedule 40 or schedule 80 PVC to combine a bit of flexibility with solid strength under roads with truck traffic. Be generous with sleeve diameters to make room for plenty of wiring and piping.
Positive drainage is extremely important. Standing water can freeze and cause falls. For smooth pavements, you need a two percent (or ¼ inch per foot) tilt so stormwater will run off the path and percolate beyond the pavement. Too much steeper, though, and you might make the slant uncomfortable to walk. Deal with the inevitable water that will fall or drain on the site while providing comfortably flat surfaces for paved areas.
Improved colored pavers and color and textural embedding techniques are available now. Once you meet the safety, ergonomic, and functional requirements for circulation within your landscape design, the geometry and design has no limits. You can use symmetry or asymmetry. What you choose to do does not have to look like anything you have seen before. The best circulation design lesson I can give you is do not feel obligated to imitate historic examples. It is time for new ideas. Much of current landscape pavement installations are copies of something from the industrial age. It is time for innovation, and you may be the inventor of the next big trend.
Sidewalks and Paths
People are generally about eighteen inches wide. Paths need to be wide enough to allow people traveling in different directions to pass each other. Five or six feet is typically the minimum width for a public pathway. Urban sidewalks are often ten feet wide or more. Existing paths can be widened by adding bands of contrasting paver units. It’s a nice look, especially if the bands match other materials in the landscape.
The soil next to a paved path needs to be flush with the pavement and fall away gently for at least five feet on either side, to avoid falls. This is a detail often forgotten on construction detail sheets. Check your drawings to be sure it is included. The paved surface needs to have a cross slope of about six feet for every one foot of drop, so stormwater will drain.
Add handrails along sloped areas. In public areas handrails need to be made skateboard proof to prevent injuries.
Paths used at night need lighting. If that lighting is combined with nearby trees, consider the trees might obscure the lighting, so space lights a minimum distance of fifteen feet from the foliage, to avoid a conflict.
Check your plans for how paths end. Swelling the width of the path at intersections looks nice and prevents damage to the beds at sharp corners.
Get the circulation right, and the landscape design falls into place nicely.