Between the Building and the Street:
Security design and the landscape architect
By: Leonard J. Hopper, FASLA
Life as we know it will never be the same after 9/11.
We have heard that expression so many times we may have even grown tired of hearing it. The truth of the matter, however, is that life has changed, and designers need to recognize and respond to that change. The attacks on 9/11 were not without precedent, though never of the magnitude and coordination witnessed that tragic day. In many ways, the attacks on U.S. embassies and facilities abroad, such as Khadar, Saudi Arabia, and more recently, the USS Cole, were but preludes to 9/11. The first bombing of the World Trade Center in New York and the bombing of the Alfred P. Murrah federal building in Oklahoma City, Oklahoma, brought the work of terrorists up close and personal to the citizens of this country...more so than ever before.
Security is a critical overlay in every major public or private design project currently being considered, and retrofitting existing facilities and sites to enhance security is a high priority. Designers are uniquely positioned to contribute to America's safety and well being, responding to the war on terror by redesigning domestic 'battlegrounds,' thereby giving us the tactical edge while taking away every advantage from those seeking to do us harm.
Dawn of a new site design era
A number of reports were issued during the 1990s in response to attacks on America. As might be expected, the lead was taken by federal agencies, but the criteria and guidelines were certainly applicable at the state/local and public/private levels. The reports acknowledge terrorist attacks can take many forms, but the overwhelming threat-accounting for approximately 80 percent of incidences-is from bomb-laden vehicles. This type of attack (for which stand-off zones were created) is thought of as the easiest way to cause extensive damage, loss of life, and possible progressive collapse of the structure being attacked.
One of the most referenced reports was Urban Design Guidelines for Physical Perimeter Entrance Security: An Overlay to the Master Plan for the Federal Triangle, issued by the General Services Administration (GSA). The varying levels of threat classified in this document, and the strategies for response presented, have become critically significant.
GSA classifies threats with letter designations (A through E), and divides a building and its site into six numbered zones. A-level buildings are considered least likely to be threatened, while E-level facilities require a very high level of protection. When this threat classification system was applied to the many public and federal buildings in Washington, D.C., most buildings fell into either a C or D threat level. (For example, a perimeter barrier for a D-level building must be able to stop a 5.4-t (6-tonne) vehicle traveling 80 km/h (50 mph]). As for the six building zones, Zone 1 represents the building interior; Zone 2, the building perimeter; Zone 3, the building yard; Zone 4, the sidewalk; Zone 5, the parking lane; and Zone 6, the street.
In new construction, a site can be enhanced with security features integrated in the architecture. Structural modifications and building hardening can be applied to existing facilities and the measures employed can be unique for every structural and architectural design. This approach, if at all possible, is usually very costly. As such, most efforts to enhance the security of existing facilities and structures focuses on the exterior zones (3 to 6), making them extremely important.
The guidelines set forth by GSA for these zones include a desired 30.5-m (100-ft) setback of the building from the parking lane (or other compensation if this is not possible). A couple of examples of compensatory design responses might include the widening of a sidewalk and elimination of curbside parking. A wide range of recommended approaches to site security are presented for Zones 3 and 4, but a few general principles are imbedded in these recommendations. Security measures taken should relate in character and context to the adjacent buildings and surrounding area, and should not impede pedestrian access. Another recommendation is enhanced security should be provided through the integration of design elements.
Heart is in the right place, but...
The immediate physical response to the attacks of 9/11 was to use just about anything heavy or strong enough to stop vehicles dead in their tracks or keep them from violating stand-off zones. The most common temporary element used was probably precast jersey barriers (used for traffic control on roadways), followed closely by large precast planters affectionately known as 'bunker pots' (actual potted plants seemed optional). This spectrum broadened to include precast drainage structures and dry-well rings (materials intended to buried in the ground) installed along the perimeter and major paths in highly visible areas around our government institutions in Washington, D.C.
The widespread deployment of precast concrete 'anything' sprinkled throughout our most valued landscapes resulted in many observers reacting negatively to the aesthetic and psychological impact. This got the attention of not just designers but government officials, who realized security measures taken to protect our people and institutions must not inflict damage to our physical, historical, and cultural heritage.
Deploying the quickest and cheapest means of protection when heightened security first arises is understandable, but the likelihood of these 'temporary' measures becoming permanent should concern us all. Knee-jerk responses can actually increase the perception of threat and instill fear, rather than promote a secure feeling. Erected barriers greatly affect the way people interact with their institutions, government, and each other.
The immediate responses to heightened security come at a high price: the price of temporary physical improvements, increased personnel and overtime costs, and the psychological impact on the citizens of our country. It is imperative we integrate security measures in our designs for new construction (or the retrofitting of existing facilities) in a way both effective and flexible to varying levels of threat. This can be achieved using familiar site elements while providing effective security in a seamless, transparent manner.
Thoughtful access control
The first step in planning for enhanced security is to perform an accurate and realistic risk assessment of a facility's threat level before considering the appropriate design response for meeting that threat. This important step is often overlooked, as there is a tendency to over-design or create unnecessary redundancies in a security design response. Not every facility nor building requires the same level of protection against potential terrorist activities.
With the objective of further refining GSA's earlier standards and coordinating the efforts of various federal agencies, the Interagency Security Task Force (a group analyzing federal security responses) identified and categorized varying levels of threat. The design guidelines they issued to federal agencies in May 2000 assigned a protection level against threat based on a building's symbolic importance, critical nature of operations, number of employees and visitors, design and construction, and consequences of attack, as well as surrounding site conditions and relationship to the street.
Currently the basis for federal policy and guidelines, these criteria allow for varying levels of physical responses to the various levels of potential threat. Buildings requiring the highest levels of protection-because of threats and potential high-speed, unimpeded perpendicular vehicular access-still require the highest (and usually most visible) physical security elements. However, buildings with a lower level of risk can be adequately protected with a much wider array of site elements that have the positive impact of enriching the streetscape while providing the appropriate level of security. In cases where the highest level of security is required, particularly where buildings are designed with vehicular entry points, heavy-duty fence and locking gates, rising vehicular barriers, beam barriers, and guard booths are still required. However, even these extreme measures to address security can be done in a manner consistent with good design principles.
The rising vehicular barrier is the most common of the elements designed to stop unauthorized vehicular entry. It can be installed as a flush mount onto existing pavements or as part of a shallow foundation system. Hinged at ground level on the protected side, and rising approximately 1 m (3.3 ft) on the attack side, this heavy-duty steel barrier rises in a matter of seconds to stop a five- or six-ton vehicle traveling 50 miles per hour dead in its tracks and still remain operational (after the vehicle is pried off the barrier, of course).
Less common (or perhaps less obvious) cantilever or track grates can be designed to withstand similar crash criteria. These gates open by sliding back parallel to the opening they are protecting. The gates open approximately 30 feet per minute, but the length of time it takes is really a product of its width, which can range from a typical opening of nine or 10 feet, to widths of 30 feet or more. Although they take longer to open, they allow wide openings to be protected from unauthorized vehicular entry, as well as restrict pedestrian travel.
Also effective in meeting established criteria for stopping vehicles is the beam-type barrier. In many ways, it resembles the typical parking lot arm barrier (with which we are all familiar), but it is something else altogether. The hydraulically powered arm locks down between two crash-rated anchors. What provides its deceptively high strength is the steel cable beam integrated into the arm. These sorts of barriers at vehicular entry points typically require a gatehouse to monitor their operation and control vehicular authorization and access. The vehicle entry point needs to be laid out in a way allowing several vehicles to line up while awaiting entry authorization without interfering with pedestrian traffic. This usually positions the gatehouse on the protected side of the vehicular barrier. Gatehouses come in a number of different functional designs and sizes one would associate with this function. However, in areas of significant symbolic or architectural importance, every effort should be made to design this structure in the context of the building it is serving and the character of the surrounding area.
Simple security elements
For scenarios requiring a less extreme approach, the site elements used to restrict vehicular access and pedestrian circulation are extensive and varied. The list starts with bollards, which come in many shapes, sizes, styles, and materials. Bollards can enhance the basic design principles of character, scale, rhythm, and harmony to a streetscape while providing the necessary perimeter security. Bollards can be fixed, stationary elements or retractable.
Retractable bollards can be lowered into the ground, by hydraulic or pneumatic power, to allow vehicular access to an area. (In colder climates, the below-ground assembly can be heated to prevent freezing up in cold whether.) Although they can be used to control access to a vehicular entry point, they are used more commonly where vehicles enter on an irregular basis. Typical uses might be to allow emergency or maintenance vehicles into an area while restricting regular vehicular access.
A typical configuration for restricting vehicular access usually employs three or more bollards, depending on the width of the opening. Spacing the bollards at a distance less than the width of a vehicle means an unauthorized vehicle trying to gain access will impact at least two bollards. Fixed bollards spaced every four to five feet adjacent to the street curb create a formidable vehicular barrier, protecting both building and pedestrians on the sidewalk from illegal vehicular access. (Bollards have traditionally been used to restrict vehicle access and have therefore accumulated the necessary test data for confirming performance requirements.)
Unfortunately, the bollard has become such a common response to perimeter security that its over-use diminishes its design value. Other site amenities can be creatively used to provide perimeter security (lest we become cities of bollards). Some of these amenities include major trees (with and/or without tree guards), benches, planters, bike racks, information kiosks, bus shelters, overhead structures, signage, and flagpoles. These are among the more common elements used to provide vehicular barriers along the street and effective perimeter security.
Building plazas and public gathering places can use these site amenities along with raised planters, changes in elevation (i.e., steps, ramps, and railings), walls, fences, colonnades, statues, and fountains. All of these site amenities can enhance and complement the character of an area and architecture of adjacent buildings, as well as provide a meaningful reason for widening pedestrian sidewalks.
We have all used these familiar design elements before, and they can be used again strategically to enhance security. This security enhancement will safely allow people to gather in our public and civic spaces, taking part in a wide variety of positive activities. These gatherings are an important part of who we are as a nation, and we must not let security concerns prevent us from coming together. Each of these elements can be beautifully designed, carefully sited with their commonplace, everyday character disguising their protective role. However, the most successful implementations consist of many elements combined together rather than depending on any one element. One should think of the vocabulary of site amenities as separate threads woven to create a fabric, resulting in a rich streetscape as well as enhanced security.
The use of these traditionally non-security elements allows a great deal of flexibility and creativity in a design response. One strategy in addressing the need to stop vehicles from speeding toward a facility is not to provide those vehicles a straight path by which they can accelerate to dangerous speeds. Carefully siting elements and changes in grade are extremely effective in preventing vehicles from attaining speeds requiring more extreme security measures. This approach then provides the opportunity to employ a broader spectrum of common site elements that can withstand the impact of slower moving vehicles.
Securing the security element
The amenities that can provide perimeter and site security, such as flagpoles and park benches, do not come with data relating to their ability to withstand impacts, nor do they meet established criteria as they are considered non-traditional security elements. (Many site amenity manufacturers are now developing products to be integrated into a security design response. As part of this initiative, the necessary testing and data will become available, making it easier to determine a product's ability to meet vehicular impact criteria and establish necessary anchoring requirements.)
At this point, many installations are tested on a case-by-case basis, and before they can be used to enhance security, they must be modified or 'hardened' to resist vehicular impacts. This may involve strengthening the element by increasing the size or strength of its components, or the way those components are connected. It most certainly would involve strengthening the manner in which these elements are usually anchored in place.
A great deal of a site element's ability to withstand an impact is at the point of connection to the pavement, curb, or footing. The size of curbs or footings may have to be increased to withstand vehicular impact. An element that might usually be anchored in a footing of concrete typically one foot square by three feet deep might now require a footing three or four feet square by five feet deep. Site features typically anchored in a footing might even require modification for anchoring in a substantial underground-grade beam to create a more monolithic resistance to impact.
Most of these hardening techniques are invisible to the casual observer, hence the value of using commonplace site amenities to enhance security. However, special considerations are necessary because of the substantial below-grade modifications. The areas typically benefiting from the use of these amenities as security measures, particularly the sidewalk to the curb line, often have underground utilities running beneath them, installed at a depth not conducive to this type of construction. As such, conflicts with underground utilities needs to be studied before embarking on a security design effort of this type.
Additionally, the increased size of underground footings, curbs, and grade beams can have disastrous effects on existing trees, and can severely limit the development or lifespan of newly planted ones. Damage to the root structure of existing trees should be minimized, and new trees should be given ample opportunity for their roots to spread. The use of structural soils to provide both a positive growing environment for tree roots and the integrity to support pavements above should be considered.
This type of streetscape improvement for security purposes often requires the removal of sidewalk pavement. As such, the opportunity to maximize a tree's ability to survive the urban environment while performing as a security element should not be missed. The location of underground utility lines and tree roots are so critical, that in some cases, they drive the location and even feasibility of streetscape elements for enhanced perimeter security.
The outlook for enhancing the security of our buildings and public spaces, as well as the aesthetics of our open spaces and streetscapes, is positive. GSA has a decade-long history of addressing security concerns and striving for design excellence. The work of the National Capital Planning Commission, represented by The National Capital Urban Design and Security Plan, provides an insightful look at the negative impact of temporary security measures. Contained in the plan are sweeping recommendations and guidelines addressing permanent design security measures respecting our nation's physical heritage, history, and culture.
Security concerns have made the integration of building architecture and site design increasingly critical. The close collaboration of architect/engineer (A/E) and landscape architect can result in both responsive and beautiful designs. Indeed, there is a growing recognition that site security measures and good design need not be mutually exclusive.
Author Leonard J. Hopper, FASLA, is the chief landscape architect and head of the New York City (NYC) Housing Authority's Landscape Architecture Division, where he is responsible for approximately 2600 acres of open space at over 350 housing developments. He is a faculty member at The City College School of Architecture and Environmental Studies, and has been a guest lecturer at Columbia University's Urban Design and Urban Planning programs. Hopper is a member of the American Society of Landscape Architects (ASLA), serving as its national president for 2000-2001. He can be reached at (212) 365-5337.
Reprinted with permission of The Construction Specifications Institute, 99 Canal Center Plaza, Suite 300, Alexandria, VA 22314, from The Construction Specifier.
This information is for illustrative purposes only and is not a contract. It is intended to provide a general overview of the plan described. Please remember only the insurance policy can give actual terms, coverage, amounts, conditions and exclusions. Program availability and coverage are subject to state regulatory approval.