Impact of September 11 on Airport Parking in the U.S.

By Mark A. Postma

Parking at airports across the U.S. has changed dramatically since the tragic events of September 11, 2001. The Federal Aviation Administration implemented security measures that closed parking within 300 feet of terminal buildings. Most U.S. airports have parking surface lots and structures within 300 feet of the terminal. Airports scrambled to close parking areas, redirect vehicles and search vehicles in restricted areas using manual methods and FAA bomb dogs. Short-term, long-term, employee, and rental car and concession operations parking was affected. Additional security personnel were assigned to patrol the exterior of the terminal buildings and parking areas. Proposed parking structures at airports in the design phase were put on hold indefinitely. The security measures had an all-encompassing effect on the use of vehicles around airport terminals.
The parking restrictions at airports were offset by the dramatic decrease in air travel. Many airports did not have parking shortages in the time period shortly after 9/11. That was of little solace as declining revenues from air travel, parking and concessions were having a major negative financial impact on these airports.
As travel began to increase toward normal levels, the availability and convenience of parking became an issue. Currently, parking revenues at many airports are still down. For an airport, losing 300 spaces averaging $10 of revenue a day can result in a monthly loss as high as $90,000.
Prior to 9/11, it was inconceivable to consider closing so much parking at so many airports for such an extended period of time. The FAA granted some relief from the security measures for smaller Category 4 airports. Medium and large airports were provided two options to obtain a waiver of the 300-foot parking restriction -- search all vehicles to be parked within 300 feet of the terminal or complete a blast assessment study.
Some airports have resorted to the costly option of searching all vehicles entering the 300-foot area. Smaller airports are paying $4,000 to $10,000 a month for this service, while larger ones are paying up to $150,000 a month. Although the revenues from the close-in parking are sufficient to pay the additional cost of security screening, the revenue surplus of these parking operations has been reduced significantly.
Some airports have retained the services of a consultant to complete a blast assessment study. Many airports waited hoping the FAA would ease restrictions while others were unsure of completing an analysis as the requirements for such an analysis may change. The parking issue has not been an FAA priority. The FAA desires to address the parking issue, but they have been very busy meeting the numerous requirements inside the terminal set forth in the Aviation Security Bill.
Requirements in the new Aviation Security Act signed into law by President Bush may alter the requirements for obtaining waivers in regard to parking and may also change the governing authority. The new law states, "If the operator of an airport ... after consultation with the appropriate state and local law enforcement authorities, determines that safeguards are in place to sufficiently protect public safety, and so certifies in writing to the Under Secretary, then any security rule, order, or other directive restricting the parking of passenger vehicles shall not apply at that airport."
This bill has two subtle changes that may affect future waivers of these security measures. Namely:
1. Change of emphasis to indicate safeguards to sufficiently protect public safety. Previous requirements were oriented toward preventing catastrophic collapse of the terminal building, not public safety and not toward limiting the damage within parking structures.
2. Assignment of responsibility to state and local law enforcement authorities and assigning the overall governing authority to the newly created position of Under Secretary of Transportation Security rather than the FAA directly. In January, President Bush appointed John Magaw for this new position that has sweeping powers. This change may reflect the feeling of many that the FAA has no legal authority regarding non-air side issues such as parking and roadway areas.
Rationale for restrictions
The purpose of the FAA mandated security measures is to protect the terminal buildings from a catastrophic collapse during a blast event in the surrounding roadway or parking areas so that airport operations may be maintained following the blast. This reasoning raises the question: "What is the probability of a blast event in parking areas around airport terminal buildings?"
One can argue that arrival and departure roadways in the U.S. are located directly adjacent to many terminals and pose a greater threat than any parking areas. Although these roadways are closer in proximity, there is perceived deterrence from visible security personnel, skycaps and pedestrians. Drive up terrorists would have to be willing to commit suicide to achieve their goals, a notion not as inconceivable as it was a few short months ago. A terrorist who would like to keep his life may view easy access to parking relatively close to a busy airport terminal as a worthy target. In an increasingly mobile society, airport facilities are major icons in many American communities representing our freedom to travel and do business.
Blast basics
Blast loadings are very different than conventional and seismic (earthquake) building loads. One major difference between seismic and blast loading is the time span of the event. Seismic events can last up to 30 seconds and "grind" the structure into the ground. Blast events last for milliseconds and are often over before the structure "feels" the effect due to lag phenomena. Explosions are rapid releases of stored energy that result in a shock wave that compresses air molecules in its path, producing over-pressure. This over-pressure is amplified by up to a factor of 12 as the shock wave hits a building. These pressures can be much greater than typical wind and seismic design pressures.
Blast characteristics are very different in open air versus confined spaces. Parking structures have varying degrees of openness or vent area and the blast response will be very structure specific. Confined and contained explosions produce very complex pressures within the structure and exiting the structure. Confined explosions include a reflected shock wave phase and a gas-loading phase. The reflected shock wave phase is similar to an open-air blast except that they are much more complex due to reverberation off various surfaces in the structure. The gas-loading phase is due to the confined space not being able to vent the gases from the explosion. The result is a much longer lasting and po-tentially more intense pressure being applied to the structure.
Blast assessment studies
Computer programs are available to estimate the effect of a blast event on a structure. One such program, BlastFX, is endorsed by the FAA for blast assessment studies for airport terminal buildings. While these programs provide good base information for open-air blasts, they may not accurately predict the effect on the terminal building of a blast within an adjacent parking structure or the effect of a blast wall. More sophisticated programs are required to consider the dissipating effect of bumper walls, upturned beams, venting, gas pressures due to confined space, etc.
Regardless of how the interpretation of the Aviation Security Act plays out, prudent owners are completing blast assessment studies of their facilities. These studies provide the extent of damage to the terminal building and parking structures, and determine the likelihood of injuries to terminal building occupants. Mitigation measures to localize the damage within the parking structure or terminal or to minimize the amount of injuries can be studied.
The future
At this time, it is not clear when the 300-foot parking restrictions will be lifted or whether other, perhaps more stringent, security requirements will be mandated. What is clear from our conversations with numerous airport executives is that there is no one silver bullet for addressing this issue. The FAA is considering each airport as a separate case and applying their best judgment on any rationale for relaxing the 300-foot requirement.
The response by the FAA varies by region. With respect to searching vehicles, different airports are being required to use different types of personnel including law enforcement officials, National Guard personnel, security companies or even rental car employees for rental car areas. The future requirements for parking at airports related to blast issues will be site specific and will vary between existing and new parking.
Existing parking -- The physical restrictions in existing parking facilities make this situation a complex issue. A security or blast assessment study provides base information on the vulnerability of an airport and its terminal and parking structures to a blast event. This information is submitted to the Undersecretary of Transportation for consideration of a waiver of the 300-foot rule. It may also spur airports to strengthen portions of their terminal or parking structures or alter current parking operations to provide a more terrorist resistant and safer site for the future.
New parking -- Future parking at airports will require designs to address these threats. The most cost-effective method of blast mitigation is to increase the standoff distance, the distance between the parking and the terminal building. This option may not be feasible for established urban airports with limited space.

Mark A. Postma, P.E., is Director of Restoration for Carl Walker, Inc. He can be reached at (800) FYI-PARK, (394-7275) or

Article Abstract from February, 2002

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