Community Research

Different type of parking lot element in the design of U.S. Cities an town.

Background

Parking lots have long been a major element in the design of U.S. cities and towns.  While it may not be true that the United States is turning into one enormous parking lot, there are times when this would appear to be the case. The popularity of the automobile as the preferred mode of transportation and the spread of industry and commerce away from the central city have combined to increase the number and size of parking lots.  The suburban shopping mall and industrial park, surrounded by a sea of automobiles, are a very familiar part of the contemporary American landscape.

The Public Benefits of Parking Lot

Parking lot landscaping needs to he encourage because it enhances the visual environment; promotes public safety; moderates heat, wind and other local climatic effects produced by parking lots; and minimizes nuisances, primarily nose and glare.  Because a properly landscaped lot can provided these public benefits, planners are legally justified in imposing landscaping regulations.

Hedges can guide automobiles and pedestrians.

Public Safety

Landscaping provision can be used to enhance the safety of parking lots by guiding the circulation of cars and people and by ensuring that the drive's vision is unobstructed.

Landscaping can be used to control access to parking lots, to make traffic diverter prominent, and to direct the flow of traffic within the lot.  When planted next to highway  or in median strips, trees and shrubs can form an effective crash barrier. Plants with thorns or needles, such as conifers are particularly effective in controlling pedestrian traffic.

By varying the species, height, and location of landscaping, the relative important of streets can be defined . For example, plants of similar height might abut major highways, while plants of variable heights and less density might be used a long minor streets.  Landscaping that serves a primarily aesthetic purpose can also be sued to promote safety by controlling views and by defining spaces, which, in turn, can influence  traffic movements.

Because improper landscaping can block sigh line s landscaping regulations frequently required that property owners limit the height of planting at intersections to make it easy to see oncoming traffic and pedestrians.  The oncoming traffic; the higher  the speed , the more time a driver needs to see oncoming cars or pedestrians.

Heavy planting, at the edge of the parking lot gives softening and cooling effect during the summer when the trees are in leaf.

Microclimate

Everyone has felt oppressive heat reflected from an un landscaped parking lot on a summer day.  Plants can have a significant moderating effect on the heat and other uncomfortable aspects o the microclimate of parking lots.  The water released from plants by transpiration and evaporation reduces high daytime temperatures, as does the absorption or reflection of solar radiation by leaves.  At night the heat that has absorbed is released of the lot has shaded by plants, less heat is  slowly, moderating evening temperatures, and, since some of the lot has been shaded by plants, less heat is released by the paved surface at night.  The amount of temperature and modification plants can provide depends to some extend an small trees more effectively moderates summer temperatures than does a planting of small ornamentals because of the multiple canopy provided by the diverse planting.

Some landscaping of parking lot can be used as buffer for adjacent streets and building to reduce nose and glare.

Minimizing Nuisances-Noise and Glare

Landscaping of parking lots can be used as a buffer for adjacent streets and buildings, reducing glare and noise.  Some people also feel that a landscaped buffer reduces vandalism of vehicles. 

since plants and trees absorb sunlight and provide shade glare is reduced by landscaping. Glare can come from primary sources, such as the sun or street lights, or from reflections form the surfaces of automobiles.  To minimize glare, landscaping must be place between the viewer and it sources. Plants might be selected on the basis of such characteristic as height and density at both their immature and mature stages of development.  Daily and seasonal variation s also must be considered to obtain the desired results.  A lack of glare is particularly critical to safe driving., and, thus  it is an important factor in landscaping around parking lots and roads.

Some parking lot has more landscape than the other.  It is depend on where the designer design and the location of it.

Amount and Location of Landscaping

The amount of landscaping needed to improve parking lots is difficult to estimate,. hat is the minimum amount of landscaping needed to screen parking from adjacent to residences? How much is needed to enhance the general environment of the parking lot itself?  There are no easy answers.  When ASPO published  the original report, Parking Lot Aesthetic, it was suggested that minimum of 10 percent of the area be used for landscaping.  This percentage was, and still is a, a generally does not provide enough area  for landscaping to be effective, so many communities still use this general rule and a recent report by New Jersey Department of Community Affairs recommends it as a minimum.

Possible of Treatment of Parking Lots Edges

The three basic materials that can be used to screen parking are vegetation, earth and structures.  The character of the area, adjacent land use, depth of setback available and cost are all determinant and appropriate solution

Trees and shrubs are planting along the parking lot.

Planting

Rapid growing vine and climbing shrubs can planted on fencing where no set back is possible. Boston Ivy or Virgin creeper will the give the most rapid coverage, though they lose their leave in the winter.  Firethorn or varieties  of Euonymus are evergreen plant that will provide all year-round screening.

Hedge maybe use d to good advantage when a narrow setback is possible. California privet is a very successful deciduous hedge plant, but require s more trimming that evergreens such as Japanese Holly or Upright Yew.  The height should be be a minimum of 6'.

Flowering trees can be used in conjunction with a low hedge where a the depth allows. Trees such as crabapple magnolia and Hawthorne would provide screening and are adaptable to city conditions.

The shrubs and plants are growing along the parking lot make it as a screen.

Earth

By combining earth and mounding with low retaining wall screening can be achieve in a a limited space where it would not be desirable to cut off the distant view.  Rip rap, sloped paving or a battered dry wall a re alternatives when they setback is slightly deeper.  Earth mounds alone may be used if a depth of 40' is available.  Lawn can be easily maintained on slopes up to 3: 1, however ground cover s such as Ivy or Pachysandra on steeper slopes (up to 2:1) would but down maintenance. 

The retaining wall of the parking lot is the most positive solution to screening the parking.

Structure

The most positive solution to screening parking would be the construction of a brick or other suitable masonry wall.  The minimum height should be six feet.  Periodic openings with panels of wrought iron fencing would allow surveillance from the outside.  Pedestrian greenways and small sitting areas could be provided where the street right-of-way width permits.

In commercial areas, a narrow band of small shops would both screen the parking and provide shopping continuity.  Careful design control would have to be exercised in this situation.

Vehicular Circulation and Parking

Vehicular circulation and parking are important site planning issues combining both function and aesthetics.  The impact of automobiles, roadways and parking on the creation of livable cities and towns has been negative.  Careful planning and site design can mitigate the damage to the physical landscape while permitting the freedom of access that Americans have come to expect.

While automobile access has been emphasized for the last 50 years, pedestrian and bicycle access has been eroded. 

Austin 2004

Road Hierarchy Table

Road Hierarchy Table

The table provided here is a reference for street width and travel speed.  Transportation planners typically establish a hierarchy of roads depending on the speed and amount of traffic.  The use of collectors and arterials to move traffic through residential neighborhoods has come into question.  Traditional street design dispersed traffic throughout the grid of local streets rather than funneling them to collectors and arterials.  This pattern seems to favor the pedestrian by limiting the number of high speed, high volume roads.

Austin 2004

Rural Freeway Cross Section

Austin 2004

Major Arterials

Austin 2004

Depressed Expressway

Austin 2004

Roadway at Flood Plain

Roadway

This section illustrates the use of low speed frontage roads adjacent to higher speed and high volume arterials.  Notice that berming for sound and visual screening is provided for.  Note also, that storm water runoff from the highway is directed into a vegetated median where it can infiltrate into the soil.

In this section the lane and median widths for an arterial road are shown.  The planted median limits the problem of glare from on-coming traffic.

The change of grade, speed and number of lanes in the depressed expressway effectively isolates parts of a city in order to move large volumes of traffic through.

Preservation of indigenous vegetation is important especially when the road is within a flood plain. Minimizing the earthwork in the median is the point of this illustration.

 Traffic Volume

The volume of traffic expected as the result of new development can be estimated by considering the typical driving habits of Americans.  The typical single family detached residential unit generates an average of 10 vehicular trips per day.  Low rise apartments generate 5.4 units per day while high rise apartments generate 4.3 trips.

This suggests that a high density and mix of residential and retail uses can significantly reduce the amount of traffic generated in an urban area.  Loop roads and cul-de-sac streets that are 20'-26' wide can accommodate 2,500 trips per day at speeds of 25 mph.  Minor connectors (local streets) that are 20'-24' wide can carry 1,500 trips per day.

Lane widths range from 12' to 10' depending on the speed and volume of traffic.  Parallel parking should be 22'x8'.

Austin 2004

Existing Highway

Austin 2004

Photo Simulation

Multi-Functional Spaces

As towns and neighborhoods develop, we sometimes forget that streets are more than conduits for cars.  They are multi-functional spaces that need to be enclosed as corridors and furnished to support their many uses.  In the top image, a state highway makes its unattractive entry into the town of McCall, Idaho.  The absence of sidewalks, curbs and plantings make this street a desolate place.  Notice also, that the buildings are held away from the street by undefined parking lots.  

The second image is a photo simulation showing the effect of trees, parallel parking and curbs.  The pedestrian is protected by each of these elements.  Cars turning into parking area must use access ramps, reducing the number of pedestrian-vehicle conflict areas. Parallel parking spaces should be 22' to 24' long and 7' to 8' wide.  A 28' wide road will accommodate parallel parking on one side.  Since the driver opens the door into the traffic lane, this is a dangerous parking method.

Austin 2004

Parking

Austin 2004

Traditional Parking

 Parking

Vehicles vary in size but autos are generally 16' long and 6' wide.  Some vehicles on the market today are somewhat shorter and longer and wider

Angled parking along the street is a pattern of small towns across America.  This  method provides a large number of parking spaces adjacent to the businesses and reduces the need for large parking lots.  This parking and road pattern also greatly reduces traffic speed which is appropriate for a central business district.  In this image, a central business street has angled parking on one side of the street and parallel parking on the other.  This arrangement compensates for a right-of-way that is too narrow to accommodate angled parking on each side.  However, both arrangements provide the pedestrian with a protective buffer from the moving cars.

Austin 2004

Curbside Lot

Curbside Lot

The site planning mistake of the 1960's and 70's was replacing angled on-street parking with large parking lots in front of the business.  This moved the building back from the sidewalk and discouraged pedestrian flow in favor of higher speed vehicular traffic.  A better solution is to place the building at or near the sidewalk edge and place the parking at the rear of the building.

In this image, you can see some other problems.  Reflected heat and glare are unpleasant characteristics of the poorly design parking lot.  Enamel paint, chrome and glass reflect sunlight into the eyes of pedestrians walking past or through the lot.

Austin 2004

Corner Parking Lot

Corner Parking Lot

The lower image shows a poor planning practice and a poorly designed parking area.  The intersection corners of central business districts should be reserved for buildings that contribute to the character of the neighborhood or the development of pedestrian spaces.  The arrangement shown creates an unattractive urban image as well as an inconvenient or hazardous parking situation.

Austin 2004

Aisles and Stalls

Austin 2004

Austin 2004

Austin 2004

Austin2004

Austin 2004

Aisles and Stalls

Dividing very large lots into smaller "rooms" separated by planted buffers makes parking lots more visually acceptable and reduces their scale.  Planted islands have been included in this lot to enhance its character.  

Asphalt absorbs a great deal of heat.  When the material is heated to above the temperature of the air, the asphalt radiates heat to the air.  A combination of direct solar radiation and long wave radiation from the asphalt can create a stifling environment in the summer.  A goal of shade over at least 50% of the asphalt at noon in the summer has been adopted by some municipalities as a minimum design standard.  You can see that the lot illustrated here does not meet that standard.

Adding a 5' extension to the dead end part of the lot helps the last two space gain an exit without backing out of the lot.  Late comers to a full lot still have to back out into the road.

This "hammer head" design solves the problem of late comers having to back out of the lot, however, there are 6 fewer space than in the dead end lot.

Here are two alternative designs for flow through lots.  On the left is the lot typical of small shopping centers.  It preserves a fire lane near the building.

Placing planting beds at the end of the parking bays and between them can transform the visual character of a parking lot.  In these images, shrubs such as, Burning Bush, Oregon Grape and Junipers, are planted in curbed planters.  Plants on the end of the parking bays should not grow taller than 4 feet to preserve the driver's sight lines.  However, even these low plantings screen the parked cars substantially. 

Due to the bumper overhang a median of 8 to 12 feet is needed to provide space for planting, lighting, infiltration beds or walkways.  Deciduous trees spaced 20' to 40' apart between the bays and in the end islands shade the lot in summer and let light through to melt snow in winter. 

A full size car has a turning radius of 20' and bus requires about 25'.  This results in a cul-de-sac that is at least 100' wide

Austin 2004

Austin 2004

Angled parking

Austin 2004

Austin 2004

Austin 2004

Parking Aisles and Stall Dimension

Angled Parking

Comparisons of perpendicular and angled parking reveal that more area is required for the angled system but more interior planting area is generated.

Angled spaces are easier for the driver to enter and exit.  In second image you can see the raised island between two rows of spaces.  With a little more width this strip could have served as a walkway to the building out of the driving area.

One way angled parking is advantageous since the travel aisle can be narrow.  Two way angled parking encourages drivers to turn left into a bay, pull through and park facing the aisle.  Angled parking is designed for all parking to occur to the driver's right

These images show the dimensions required for 45 degree angled one-way parking. Notice the overlap required where rows of spaces meet.

This lot pattern and dimensions are required when a parking lot is on land that slopes more that 4% or 5%.  A steep grade can occur in the median allowing for flatter aisles and parking spaces.  Notice in this scheme, the width for the pairs of bays is 50'

60 degree parking is the most common type of angled parking.  In this plan the curb to curb dimension assumes that a bumper overhang is available.  The longer dimension (wall to wall) is based on no bumper overhang.

A typical parking space is 18' by 9' and small car spaces are 16' x 8'.  Most cities and towns permit a certain percentage of small car spaces in parking lots.  This plan and table provide the dimensions of the parking lot elements for three alternative stall orientations.  Study the names and typical dimensions of each parking lot element.

Austin 2004

Parking and run off

Parking and Storm Water

Since standard asphalt is impervious, rainwater runs off at a rate far more rapid and in greater quantities than under pre-development conditions.

Furthermore, run off from streets and parking lots is contaminated with a variety of chemicals including hydrocarbons and heavy metals.  It is desirable to clean this toxic water as much as possible before it reaches the natural environment.  Vegetated swales and detention basins in parking lots have proven effective in removing pollutants from storm water run off.

The parking lot design shown here is of the University of Idaho Sweet Avenue parcel.  It is different than what was installed but has many features to recommend it as an ideal design (Kaori Yoshida, designer). 

The large lot is divided into smaller spaces.  Unit pavers on sand is used for the parking bays and porous asphalt is specified for the aisles.  These paving systems are permeable and greatly reduce runoff.  Runoff which does occur is directed toward swales and detention basins where it infiltrates in to the soil.