Designing Parking Lots
With virtual seas of asphalt seeming to stretch from horizon to horizon, some would say we have sacrificed far too much of our world to the automobile. But the effective design of parking lots is essential to the proper functioning of 21st Century cities and urban society. And, when done right, the design of parking lots can help improve our world. Let this architect tell you how (or see rickzworld).
The initial question posed by the parking lot designer is: how many parking spaces? The quick and seemingly easy answer is provided by any number of traffic and parking studies conducted over decades, by researchers having a broad range of interests. Often the results of such studies end up embodied in local zoning ordinances as minimum parking requirements. These typically vary by locality, land use and building function. In a given community, for example, one might encounter requirements such as these: retail buildings shall be provided with 5 parking spaces per 1,000 square feet of gross building area, or, restaurants shall be provided with 1 parking space for every 4 restaurant customer seats, plus 1 parking space for each employee in an average shift. Parking requirements such as these — along with requirements for handicapped parking, truck loading/unloading spaces, trash hauling and emergency vehicle access, and suitable circulation drives — quite often constitute the most detailed and extensive strictures placed on the design, development and construction of a large commercial or residential property. Such is the prevalence and power of our almighty automobile.
There are, however, several major problems with such strictures. First, they are almost always stated as absolute minimum or threshold requirements, with no permitted flexibility or adjustment to the particulars of project, use, locale, site, demand, surrounding development, transit opportunities or community goals. Second, such minimums are usually developed by those with a vested interest in optimizing vehicular traffic flow, often at the expense of pedestrian activity, transit options, convenience, green space, and aesthetic considerations. Third, these minimums grew into being throughout the time of the auto's ascendancy and ubiquity in America, the 1950s through 1980s, the growth-spurt years of the interstate highway system. Such 'standards' are therefore inherently biased towards more cars, more parking, more roads and drives, and more asphalt. Today's reasoned designer must bear all this in mind, and must flex the 'accepted wisdom' of parking requirements to meet the needs and desires of tomorrow. He or she must design 'holistic' parking lots that consider multivariate design objectives.
After determining approximately how many parking spaces a parking lot should ideally contain, the designer then moves on to consideration of a number of factors that can significantly affect the lot's layout and design. These include the obvious considerations of approximate location of the parking lot on the site, optimal locations for entering and exiting drives, the desired clustering of handicapped parking spaces adjacent to building entrances, and the provision of suitably situated truck loading/unloading areas. Other straightforward design input includes setbacks required from surrounding streets or adjacent properties, and limitations imposed by site grading, retaining walls, on-site stormwater management areas, wetlands, preserved landscaping, rock outcroppings, and the like. But other not-so-obvious parameters can also drastically affect layout and design. Will there be areas of reserved or preferential parking? Will such areas be gated, or require key-card access? How must the site layout accommodate a bus stop, pick-up/drop-off areas, projected canopies, or drive-through services with their queueing lanes? How and where can an ambulance circulation loop easily enter the site, access building entrances, and depart the site? If required, how would large fire-fighting equipment maneuver and operate on-site? What would be the optimal circuit for trash hauling or delivery services? In hot climes, where and how is vehicle or pedestrian shade provided? Will repair access to underground utilities require tearing up the parking lot? If a structure might conceivably be subjected to a terror threat, how far must parking or drives be kept from the building, and how might access be controlled?
Often the consideration of all of these varied determinants results in not one single parking lot design, but instead a range of parking lot designs, each with its own particular benefits and detriments. Inevitably trade-offs must be made — typically, loss of parking spaces vs. gain of amenities or benefits, or loss of parking spaces vs. suitable control of costs. But no matter what kind of parking lot designs (or trade-offs) result, there are certain identifiable universal 'best practices' in parking lot design:
1. The greatest efficiency of layout and use of land area, as well as the greatest overall parking safety, results from 90-degree parking in double-loaded aisles. That is, everyone parking must make a 90-degree turn from a drive into a parking space, and every aisle is a two-way driveway allowing one to park to either left or right from that driveway, where one will typically come face-to-face with a vehicle parking from the next aisle over. Parking that is angled from the drive aisle, whether at 60-degrees or 45-degrees or any other angle, not only consumes more overall land area, but also invites greater driver error and more accidents. One-way driving aisles are notoriously inefficient, as well as annoying to drivers, and in fact are prohibited by some communities' ordinances.
2. Lots using 90-degree parking on double-loaded aisles use less land per parked car than other layouts, thereby reducing not only the distance the average parker must walk to access a building, but also total stormwater runoff that must be captured and dealt with by sewers and stormwater management areas, as well as the heat island effect created by an expanse of asphalt or concrete.
3. Parking lots must also be punctuated regularly. Nearest to each primary building entrance cluster the handicapped parking spaces, with their attendant access aisles, crosswalks, ramps and signs. Retail and grocery stores must provide a sufficient number of distributed cart corrals to rein in their wayward shopping carts. Hotter-climate lots demand regular spacing of shade trees to cool long-standing cars and long-suffering pedestrians. Most communities require some green space or landscape interruption of parking seas; throughout much of Florida such green space or landscaping (internal to the overall parking lot) will consume 10% to 20% of the total parking lot area. Parking lot light poles, electrical transformers, site utility connections, hydrants, trash dumpster enclosures, ATMs, mailboxes, bicycle racks, moped parking areas, or pedestrian benches may share or may each command their own footprint island.
4. Parking lot islands are also essential to smooth and safe internal flow within a parking lot. An end island (capping the end of a double row of parking spaces) that measures 10' wide x 38' long, with circular-radiused ends, will provide for easy and comfortable turning movements for any vehicle negotiating its way around that end island. It automatically creates safe 'vision triangles' at drive intersections, where meeting drivers can suitably anticipate, see and be seen by one another. It will also afford enough area for landscaping relief, the placement of one or two shade trees, and some percolation of stormwater into the earth below. When placed often throughout a parking lot, similarly sized parking lot islands provide substantial visual and heat relief to parkers and pedestrians alike, and accommodate the aesthetic embellishment of an effective landscape design.
5. Parking lots work best, and are safest, when they are ringed by a 'cruise lane' or perimeter drive that 'collects' cars from all the intervening parking lot aisles before dumping them onto primary drives or surrounding arterial streets. Drives must be ranked and prioritized: the innermost parking lot aisles have the greatest mutual interaction and intersection, and are therefore of the lowest speed; intermediate drives can bear slightly higher speeds and smoother flow only if the numbers of their intersections and interactions are restrained; to have the greatest safe speed and flow, primary drives must have the fewest intersections and interactions. When optimized, a parking lot plan should have an apparent order, hierachy and logic to it.
6. As we ask more and more of our parking lots (and spend more and more ON our parking lots), parking lot materials continue to evolve. Asphalt gives way to concrete, both so that we can gain the environmentally-friendly benefits of locally-sourced concrete and incorporated fly ash, and so that we can increase reflectivity of solar radiation to minimize the heat island effect that adds to city smog. Permeable pavement materials come into use to allow more water to percolate through to earth, rather than run off to be collected, piped elsewhere and treated. A richer palette of colors and landscape materials comes into play for greater beauty and aesthetic effect, as well as for better sun-shading and more water-conscious plantings.
7. The parking lot edge nearest building entrances deserves the greatest care and attention. Should its bounding drive have a parallel curbed sidewalk, or should the entire drive edge merely flare upward slightly through a change of paving material, like an incredibly wide handicapped ramp (as is now often done at retail store entrances)? How have pick-up/drop-off areas, canopies, handicapped access, emergency vehicle access, and restrictions on stopping or parking been integrated? Does a building entrance appear more inviting to the auto than the pedestrian? Are there pedestrian-friendly safe zones at building entrances? benches? plantings? lighting? bike racks? Only when the designer has provided meaningful answers to such questions can the parking lot truly be complete.
Author Rick Zimmerman is a Cleveland architect, land planner and designer with nearly 40 years of experience in planning parking lots.
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