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Avoiding tort claims in parking lots.

THIS discussion of design, operating, or maintenance defects in parking facilities is intended to aid engineers and architects in avoiding many common mistakes. Certain design features could at first blush appear proper or desirable, whereas in practice they cause problems. They may simply reduce efficiency or they may cause personal injury. In either case, designers and property owners should become aware of hazardous practices and avoid them. Many lawsuits are filed each year alleging defects in parking lots. These fall into two general categories:

* Pedestrian falls (trips and slips).

* Vehicle collisions, including fixed objects and pedestrians.

Conditions or elements primarily related to pedestrian falls include: wheelstops; handicapped ramp cross slopes along sidewalks; drainage (in northern climates) as related to snow and ice control; and lighting.

Elements that may relate to either vehicles or pedestrians include: driveways; sight distance; end islands; outer boundary protection; yellow stall marking; separate pedestrian walks; and barriers between parking modules.

While a few vehicular/pedestrian collisions occur, a significant pattern of such accidents has not been found. Many vehicular accidents do happen, both at driveways and within parking lots. Vehicle drivers also may strike various fixed objects if unmarked or unprotected or they may run into buildings and entrances.

Most of the types of hazards reviewed in this article have been involved with alleged defect claims investigated by the author. Furthermore, most of the faults involve violations of simple engineering principles and/or common sense. The following detailed discussion is broken in three general areas; Pedestrian Falls, Vehicular-Pedestrian Hazards, and Miscellaneous Vehicle Hazards.

Pedestrian Falls

Wheelstops. The common wheelstop is involved with many falls in parking lots. Wheelstops are typically constructed of concrete, metal, plastic, or wood, such as railroad ties. Problems with their use have been identified for many years. Parking Principles,|1~ stated the following in 1971:

"In general, the ends of parking stalls within lots can be marked in a satisfactory fashion by only a paint line. Wheelstop blocks or curbing in the interior of the lot have many disadvantages: they may interfere with and present a hazard to people walking between cars, provide traps for blowing debris, and interfere with snow plowing in northern areas."

The same disadvantages were identified in Volume III of Automotive Engineering and Litigation.|2~ It is pointed out that the car can be easily driven over such a wheelstop. If used individually (rather than butted in a continuous row), vehicles may park at angles with one wheel past the wheelstop, thus allowing bumper overhang beyond the designer's intent. William English also addressed this subject and stated, "The presence of wheelstops in new parking lots is prima facie evidence of negligent design."|3~

The type of fall associated with the conventional wheelstop is, of course, the trip. There are several reasons for such falls occurring, as contrasted with the stepping up or down at a conventional raised sidewalk. First, the wheelstops may be unexpected. They require the foot to be raised and then lowered; i.e., they must be walked over rather than mounted or dismounted from as is the case of a raised sidewalk. If the wheelstops are in the direct pedestrian path, such as projecting out into the areas between adjacent parking stalls, or at ends of parking rows, they present a special hazard. They may blend in with the pavement. Even if they are painted yellow, they may not be readily identified if yellow is also used for painting stall lines. The toe of a pedestrian can go into the drainage opening slot commonly found in many wheelstop designs and thus cause more than a "simple" trip.

Many wheelstops are being used immediately adjacent to sidewalks along the fronts or sides of buildings. This represents a particular problem. Some form of restraining device, such as a raised walk, closely spaced posts, wheelstops, or highway guardrail is needed. Of these, the raised walk is best. Posts are less desirable because parkers shy away from striking them and thus project further into the access aisle. Wheelstops are not desirable for reasons discussed above and guardrails block pedestrian passage.

From this discussion, one can conclude that locations where wheelstops should generally not be used include the following:

* As an additional setback for sidewalks, next to the buildings, or as the sole restraining element (with flush walks).

* Within the lot, except for outer boundaries.

* Around objects such as fire hydrants.

* To form end islands.

When parking is allowed at an angle alongside buildings, raised walks are preferable. They should be five to six in. high and at least six ft wide (to allow for vehicle bumper overhang). If merchandise is to be displayed for sale in the sidewalk area next to the buildings, then additional width is needed. If a canopy is erected over the sidewalk with vertical columns, then these columns should align with parking stall lines and should be set back about three ft from the edge of sidewalk against which the wheels of parked vehicles make contact.

One place where wheelstops can be effectively used is the outer boundaries of parking facilities. Pedestrians typically would not be walking over the blocks at these locations--particularly if adjacent to a fence. When an outer boundary condition is to be protected, such as a fence or a public sidewalk, then continuously butted wheelstops are desirable. This is especially important if the parking angle is less then 90 degrees.

Wherever wheelstops are used, effort should be made to distinguish them from the surrounding surface. This is usually done by use of yellow paint, which has a cautionary effect. It is most effective when parking stall lines are painted the standard white.

Handicapped Ramps. Where parking stalls abut sidewalks, handicapped ramps have often been provided and indeed are specified in certain laws, even though the actual need may be highly limited--legal and handicapped group claims to the contrary. The ramp may be of assistance to an occasional wheelchair user, but they can be a constant source of hazard and falls for pedestrians attempting to utilize the sidewalk parallel to the building. The primary problem is the abruptness of the transition from the level walk, to the transverse upward slope of the handicapped ramp. The American National Standards Institute has established guidelines for appropriate construction of the flared sidewalk slope parallel to normal pedestrian usage.|4~ This is illustrated in Figure 1. The 10 to 1 slope as shown produces a five ft flare for a six in. raised sidewalk, whereas many of these ramps have been constructed with flares of as little as six in. Many pedestrian falls have occurred as a result of such substandard construction.

The sloped sides of the sidewalk at the handicapped ramp should be painted yellow. Of course, the paint should be mixed with a fine abrasive so as to produce a skid resistant surface with a static coefficient of friction of at least 0.45 for a dry surface.|5~ This coefficient is the ratio between the force required to start an object moving on a given level surface, divided by the weight of the object.

Lighting. Lighting of parking lots is commonly supplied for two basic reasons--to minimize the probability of pedestrian falls and to increase security relative to personal assaults. Lighting also may aid drivers in avoiding conflicts--especially with pedestrians and fixed objects.

For pedestrian walking purposes, a maintained average of about 1.0 HFC (horizontal footcandles) should suffice, with the low point of illumination being at least one-sixth of the average, or 0.17 HFC. It is important to emphasize the term "maintained." This represents the average illumination in the parking facility, when the glassware of the luminaires is at its dirtiest and just before the lamps are replaced. To minimize capital and energy costs, it is obviously important that lighting equipment be cleaned periodically and lamps replaced on a regular group replacement basis. The frequency of cleaning needed will be a function of the atmospheric environment, the mounting height of the equipment, and the volume of vehicular traffic. Typically, an annual washing will suffice. Group replacement of lamps should occur at a point 70 percent to 80 percent into the manufacturer's rated lamp life. Street lighting lamps burn about 4000 hours per year. If parking lot lights are left on all night, then group replacement about every three years would apply to many types of lamps. If the parking lot lights are burned for shorter periods of time, then the group replacement schedule would be proportionately longer.

The illumination values apply to an open, unobstructed area without any parked cars. With vehicles parked, shadows and lower minimum levels will occur between cars. This is inevitable since it is not practical to hang lights every nine or so ft apart nor to mount them high enough to throw light between all cars. Despite the shadow conditions, the recommended illumination level should provide reasonable visibility.

When pedestrian security from assault is the primary concern or reason for the lighting, up to 2.0 HFC may be appropriate. There is also a need for VFC (vertical footcandles) in terms of facial recognition of a potential assailant, but guidelines based on adequate research are yet to be developed. A suggested value is one-half the HFC (except facing outward along the lot boundary where no value would apply).

Again, the illumination levels for pedestrian security are desirably not less than one-sixth of the average value, at the lowest point. Also, the values are measured for an open condition without any parked vehicles.

Relative to vehicular needs, lighting is particularly valuable at driveways and ramps.

The foregoing recommendations vary significantly from those developed in 1984 by the IESNA (Illuminating Engineering Society of North America), RP-20, Lighting For Parking Facilities. The IES hypothesized that lighting needs in parking lots should vary depending upon pedestrian activity--similar to the variation by type of roadway for conventional street lighting. The IES values are based upon the low point being not less than one-fourth the average, and use of an average illumination ranging from 0.8 to 3.6 footcandles for pedestrian areas. However, there is no research to support this recommendation. The 1.0 to 2.0 HFC range in values as suggested by the author was recommended by the IES prior to 1984. Also, it fits with typical conditions recently measured in the field, relative to maintained illumination levels actually being provided in parking lots. It is thus "state of the art" practice.

Drainage. Problems of inadequate drainage relating to ice formation are obviously a concern in northern climates. If the slope is too flat, even small birdbaths (minor depressions in the pavement surface) can retain rainwater or snow melt runoff. Until this deposit has evaporated, it can freeze when the temperature drops. Also, it can retain ice or packed snow after normal plowing activities.

For appropriate drainage, AASHTO (American Association of State Highway and Transportation Officials), recommends minimums of 0.3 percent to 0.5 percent and greater for portland cement concrete gutter slopes. Such grades will not adequately drain larger areas because of the difficulty of construction control and the almost inevitable settlement conditions. For flexible base, asphaltic concrete construction, minimum grades of 1 percent have been recommended by the Institute of Transportation Engineers.|6~ Other sources in the parking field have recommended 2 percent as the minimum; however, this is often difficult to achieve in relatively flat terrain. Some birdbaths will be inevitable with any flexible base pavement. These conditions may require salting (calcium chloride preferred) to reduce the ice hazard.

Slopes of more than about 3 percent also should be avoided in directions longitudinal to parking stalls (to minimize rollback problems), or 5 percent for cross slopes or aisles. Ramps should utilize skid resistant pavement and not exceed about 12 percent.

Vehicle and Pedestrian Hazards

Driveways. Most driveway accidents are the vehicle-vehicle type.|7~ Up to about 14 percent of public property accidents have been found to involve driveways.|8~ The majority of accidents involve vehicles turning in from the street by left turns or out from the driveway by left turns. The remainder, involving right turns in and out, are related to driveway widths and/or the radius on each side. Other accident causes are sight obstructions, which are the major element in the few pedestrian-vehicle or bicycle-vehicle accidents that occur at driveways.

Good design practice has been developed by the ITE (Institute of Transportation Engineers) Guidelines for Driveway Design and Location, 1985.|7~ Figure 2 illustrates appropriate design criteria for two-way commercial driveways.

The hazards associated with left turn entry into a parking facility can be significantly reduced by provision of a left turn lane on the street. Accidents involving left turn exit from driveways may be reduced, in the case of higher volume driveways, by traffic signal control, where warranted. These warrants are described in the Manual on Uniform Traffic Control Devices.|9~

The control of radius and channelization immediately inside the parking facility is best done by use of raised curbing. However, the curbing is generally required to be depressed across the public sidewalk in deference to possible handicapped usage.

Sight Obstructions. No objects such as vegetation or ground mounted structures should be located in the range of approximately two ft above grade to six ft above in the areas adjacent to driveway exits onto the public sidewalk or at interior intersections of parking access aisles with cross aisles. If a driveway is primarily serving truck traffic, the lower limit of foliage trimming for trees should be about eight ft above grade.

Because of the uncertainties of maintenance such as shrubbery trimming, it is good practice to use only ground cover in areas where sight line control must be maintained. Low growing trees should be avoided--especially evergreens. It is also good practice to avoid rows of closely spaced trees where future growth might produce sight obstructions of the "picket fence" variety.

Driveway exits between buildings usually involve severe sight obstructions and therefore will generally require STOP sign control. In any case, it is undesirable to have buildings abutting a public sidewalk directly adjacent to where a driveway or alley exits onto the street.

End Islands. Islands placed at the end of parking rows have several advantages. Curbed islands were identified in Parking Principles|1~ to serve the following functions:

* Limit parking encroachment into cross aisles.

* Open up sight distance at intersections of cross aisles with access aisles.

* Provide a comfortable turning radius.

* Provide a cart storage area at supermarkets.

* Store limited quantities of snow.

* Protect directional signs and allow light pole locations; and

* Allow esthetic plantings to avoid a "sea of paving" appearance.

When used along the edges of ring roads in regional shopping centers, the end islands may also help to define the circulation and roadway system. At least one study has identified a higher accident rate for regional shopping centers without end islands, as compared with ones having such islands.|10~ The average parking capacity of these centers was 4700 spaces. This contrasts with another study of 116 parking lots used by commercial development, which found that only 7 percent of the accidents involved aisle intersections.|11~ However, the average capacity of these lots was only 140 spaces, with the largest lot being for a community shopping center and having less then 1500 spaces. These two studies suggest that, while end islands are of significant benefit to very large parking facilities, they are of limited value to the smaller ones. In parking lots for only a few hundred spaces, the driving distance in the cross aisles is relatively short and vehicle speeds are therefore relatively low. This contrasts with the ring road of a regional shopping center, where 35 mile-per-hour operating speeds are not unusual (regardless of any posted limits to the contrary). Where used, curbed end islands may be alternated with painted ones in any facility and still be effective.

An important design consideration is to limit the length of the island. The vast majority of such islands are constructed too long. By extending significantly past the end of the parked car, they may create a situation inviting a pedestrian trip and fall. They may seriously interfere with the maneuvering area available for cars to turn in and out from the parking maneuver aisle to the circulation or cross aisle. Recommended lengths of about 12 to 13 ft each side of the parking base line were given in Parking Principles more than 20 years ago.|1~ These same designs are carried forth in the 1993 design criteria for parking facilities.|6~ Figure 3 gives recommended design lengths.

Sight obstructions should not be placed in end islands.

Boundary Controls. These controls may be provided for several reasons:

* Limit access to specific points.

* Prevent encroachment of parked vehicles onto adjacent property, public sidewalks, streets, or alleys.

* Protect adjacent landscaping.

* Prevent parked vehicles from rolling (forward or backwards) into hazardous areas or down steep slopes.

In all cases, the standard highway guardrail will provide an extremely effective positive barrier. However, for both esthetic and economic reasons, the boundary protection is most often a curbing or row of butted wheelstops. In either case, the inside face of the boundary control should be set back about 2 1/2 or 3 ft from the outer limit. In some cases high screening shrubbery or walls are used. For such conditions near a driveway, these should be set back about eight ft from the public sidewalk to give a clear line of sight for the exiting driver, relative to pedestrians on the sidewalk. This also usually allows at least a minimum sight distance relative to vehicular traffic on the public street.

If a positive control must be provided, such as where a severe drop-off exists, then guardrail, structural posts, or a structural wall is appropriate.

Speed Bumps. The use of speed bumps is undesirable in any place. They can create vehicular accidents, interfere with emergency vehicle access, and present a trip and fall hazard to the pedestrian. Knowledgeable drivers of larger cars have found that, by increasing speed, the car will pass many bumps with less effect than if driving more slowly. It thus can increase at least some vehicular speeds. If the bump is made of asphalt, it may be nearly invisible. Several accidents are known to have occurred as a result of a motorcycle striking a speed bump and being thrown out of control. Others involve tripping.|11~ Speed bumps can be slippery if painted to improve identification, especially when wet.|3~

Yellow Stall Markings. Use of yellow paint is appropriate for road centerlines, along the left edges of one-way roads, to delineate "no parking" areas, and for the marking of hazardous fixed objects, raised curbings, or edges of sidewalks, etc. However, the appropriate color for parking stall line markings is white. This is the color specified by the MUTCD for use along streets.|9~ Restricting the use of yellow to its more appropriate applications increases the target value. When all lines and curbing in a parking facility are painted a uniform yellow, the cautionary value of the color is depreciated.

Parking Layout Angles. Vehicular/pedestrian conflict occurs along the building frontage, between pedestrians walking to or from their parked cars, and drivers circulating to or from parking access aisles. This conflict is minimized by a 90-degree parking layout. At any lesser angle, in busy times, drivers parked in rows oriented toward the building must loop into the building frontage roadway to access an exit aisle. Thus, when the size and shape of the parcel permits, 90-degree parking may be preferred over the common 60-degree layout. One study of parking lot accidents found the accident rate for 90-degree parking in medium and high turnover lots to be much lower than for 45- and 60-degree layouts.|12~ Other advantages of 90-degree parking are cited in Parking Principles.|1~ However, such findings do not imply that 60-degree parking cannot or should not be used.

Barriers Between Parking Modules. Owners of some large parking facilities have strung ropes or cables along the center lines of rows where vehicle bumpers abut. The theory of such an application is apparently to prevent vehicles from driving across access aisles. However, no real need has been found, since less than 1 percent of the accidents in the one study where this has been analyzed were due to such movement.|12~ Thus the use of wheelstops, curbs, ropes, or other impediments to cross movement and to cleaning, to snow plowing in northern areas, or to freedom of pedestrian movement, does not appear justified.

Separate Pedestrian Walks. In a few older parking facilities, parking rows abut separate walks which then lead toward the buildings. Because most pedestrians tend to walk up the parking aisles, the use of separate pedestrian walks in this fashion is usually not necessary nor even desirable (they provide a step-up-and-down condition for pedestrians crossing from one parking row to another).

Along certain access roads, sidewalks are desirable. Such walks would be oriented to the external sidewalk system along the city streets and to sources of pedestrian generation. Since the access roadways carry the bulk of traffic and it is moving faster than in the parking maneuver aisles, the need for such walks may be self evident.

Other locations for sidewalks within parking facilities are of course along the typical fronts and sides of buildings that will be utilized by persons walking to and from the parking row where their vehicle is located.

Building Front Crosswalks. Painted crosswalks may be considered where pedestrian concentrations occur. In most cases, however, parking aisles are oriented toward the building, and a walk is placed along the building frontage. Pedestrians should use this walk until opposite the row where they are parked. Occasionally, a special lot design with barrier curbing may generate nearly all crossings at a specific point. A painted crosswalk may reduce hazards for such a condition, but this cannot be said with certainty. Stop signs may be used, but no studies have found them to be effective. In fact, such signs are often violated by drivers--perhaps because there is no vehicular conflict situation.

Miscellaneous Vehicle Hazards

Fixed Objects. Parking lots may contain unmarked fire hydrants, utility poles, light pole bases, or sign posts. Where these are not surrounded by raised curbing or otherwise defined they may pose a hazard--especially at night. This can be reduced by the use of reflective panels or paints. Even a simple device such as bicycle-type reflectors attached to the four sides of a wooden utility pole may reduce chances of collisions. While a street light may be mounted on a pole, if it is on the opposite side from the direction of approach it may leave the back of the pole in complete darkness--especially under rainy weather conditions.

Where parking is permitted all along the face of a building, but not at the building entrance, a problem may exist in relation to unwanted vehicular intrusion into the front door. The use of wheel stops at such locations is undesirable. The appropriate design is to have a raised sidewalk--often as part of an island jutting out between adjacent parking stalls. If this is not practical, then the use of raised posts spaced not more than four to five ft on center will provide for adequate pedestrian access but yet prevent typical vehicular intrusion. This applies where the entrance is a niche in the parking row. Many entrances are constructed to service parallel stopping of vehicles to pick up and discharge passengers. For such conditions, use of posts would not only be undesirable but likely would create problems with door opening and/or add a collision hazard. A raised walk is most appropriate.

Any part of a building may be struck in parking lots, even when raised walks have been used. There is generally no practical way to totally eliminate such contacts and still maintain an environment accessible to the average pedestrian. Thus provision of a reasonable control, such as a raised sidewalk along the building front (and sides if marked for abutting parking), is all that is generally appropriate.


1. Parking Principles, Special Report 125, Highway Research Board, 1971.

2. Automotive Engineering and Litigation, Volume 3, Garland Law Publishing, New York, 1990.

3. English, William; Slips, Trips and Falls; Safety Engineering Guidelines for the Prevention; Hanrow Press; Del Mar, California, 1989.

4. Providing Accessibility and Usability for Physically Handicapped People, ANSI, A117.1-1986; American National Standards Institute, New York.

5. Proposed Slip Resistance of Floor Surface Materials, UL 410, Underwriters Laboratories, 1991.

6. Guidelines For Parking Facility Location and Design, a Recommended Practice of the ITE, 1993, Institute of Transportation Engineers, Washington, D.C.

7. Guidelines For Driveway Design and Location, A Recommended Practice of the Institute of Transportation Engineers, Washington, D.C., 1985.

8. Driveways, Chapter 5, Traffic Control and Roadway Elements--Theft Relationship to Highway Safety/Revised; Highway Users Federation for Safety and Mobility; Washington, D.C., 1970.

9. Manual on Uniform Traffic Control Devices, 1988 edition; Federal Highway Administration; Washington, D.C.

10. Nunez, A. and Parsonson, P.S.; "Safe Design of Parking Lots for Regional Shopping Centers." In Compendium of Technical Papers; Institute of Transportation Engineers; Washington, D.C.; September 1979, pp. 79-84.

11. Rosen, S.I.; The Slip and Fall Handbook, Hanrow Press, Del Mar, California, 1983.

12, Box, P.C.; Parking Lot Accident Characteristics, ITE Journal, December 1981, Institute of Transportation Engineers, Washington, D.C.
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Author:Box, Paul C.
Publication:Public Works
Date:Jan 1, 1994
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