Landscape Architecture and the Site Security Design Process  

Courtesy of the American Society of Landscape Architects
Excerpted from Landscape Architecture Technical Information Series (LATIS) publication Security Design and the Landscape Architect

Updated: 
09-08-2016

Introduction

Security concerns have made the integration of building architecture and site design increasingly critical. The close collaboration of architect, landscape architect, security specialist, and structural engineer can result in both responsive and inspirational designs. Indeed, there is a growing recognition that site security measures and design excellence, need not be mutually exclusive.

The immediate physical response to the attacks of 9/11 was to use just about anything heavy or strong enough to attempt to stop vehicles dead in their tracks or keep them from violating stand-off zones. The widespread deployment of precast concrete 'anything' sprinkled throughout our most valued landscapes, resulted in many observers reacting negatively to the aesthetic and impact. In many cases, the heavy objects were still not effective, as illustrated below.

The environments we build today in response to security concerns will reflect the values and ideals of the free and democratic society we are committed to protect and preserve.

Deploying heavy objects of any kind to deter vehicles from unauthorized entry to a site was a typical response
to the events of 9/11:

In front of the US Capitol building the guard house is shown next to a red stoplight with concrete planters (without plants) and pre-cast concrete drainage structure rings as barrier protection
Concrete jersey barriers line a road and partially block it aling with a Chevy Suburban

A combination of concrete planters (without plants) and pre-cast concrete drainage structure rings protect the guardhouse and augment the vehicular plate barrier.

Concrete jersey barriers line the road and partially block the road with the Chevy Suburban serving as a rolling gate to allow authorized vehicles to pass.

Description

Overview of Threat/Vulnerability and Risk Assessment

One basic premise of security design is that it is not possible to totally eliminate all risk. The goal of good security design is to balance the security design implementation with the likelihood of an occurrence in a prioritized approach that results in the acceptance of a conscious and acceptable level of risk to the client.

All buildings and sites do not require the same level of protection. Nor can the security of all buildings and sites be addressed with the same "one size fits all" or "cookie cutter" approach. Each building and site has a unique set of characteristics that need to be evaluated in order to develop a design that meets the desired security level.

In order to determine a building or site's level of risk, the value of the asset, identification of possible threats, and the building or site's vulnerability to those identified threats need to be evaluated. The results of that evaluation provide a basis for the implementation of a security design that achieves the desired level of protection. (See WBDG Threat/Vulnerability Assessments and Risk Analysis)

Security Design Goals

The primary goal of a security design approach is to minimize the loss of life of the building's occupants. The most effective way to achieve this goal is with a comprehensive and coordinated, multidisciplinary approach to address security in the earliest phases of site selection and/or the design process.

Site Design Considerations and the Project Team

The areas of specific consideration include off-site evaluation of land uses and relationship to security; site planning and building configuration and location; setback distances; access control; and parking. Many of these considerations, such as initial site selection and the orientation of the building(s) on the site, must take place early in the design process. The later integration of setbacks, access control, activity areas, and utility placement will be facilitated by their consideration at the earliest stages of design development. This requires that a design team, that includes the architect, structural engineer, landscape architect, security specialist, among others), work closely with the building owner from the inception of the project to ensure coordination and cost-effectiveness of the site security design strategy.

Out of Site, But Not Out of Mind

Off-site evaluation of land uses and their relationship to security is a critical first step in evaluating an existing building or making a determination on an initial site selection. The physical characteristics of the surrounding area, types of buildings and occupancies, and types of activities need to be looked at as they relate to the security of the site and/or building being evaluated. Some of these factors may have positive security implications, while others may be negative.

The types of buildings, occupancies, and uses can be of concern if they are viewed as potential high profile terrorist targets. Although the site and use being considered for development may not have these characteristics, being adjacent to a high profile target raises concern about the possibility of suffering collateral damage from an attack on the high profile target. Proximity to major transportation routes such as rail lines, highways, and waterways need to be evaluated as to their potential value as terrorist target and possible collateral impact on the development site. Existing infrastructure including tunnels, utilities (particularly the larger storm water pipes), easements, and right of ways, as well as any planned changes, should also be evaluated as to their potential value to terrorists planning an attack.

The topography and land characteristics of the surrounding area can have both negative and positive implications. The presence of natural physical barriers such as water features, dense vegetation, and rough terrain can help provide access control. The incorporation of water features, planting, and grading to create new topographic landforms in the site design can enhance a site's security where these features do not naturally occur.

Topography and climate characteristics can affect the performance of chemical and biological weapons. As wind moves through the landscape, topography and objects in its path have an effect on wind patterns. There are prevailing winds in each of the seasons where the wind comes from predominately certain directions. A variety of wind type diagrams document the direction and frequency of winds at different times of the year. This can be a useful resource when focusing on what the potential threats may be upwind of a particular site. In addition to prevailing winds, how objects and topography create changes in wind patterns can also be important. The evaluation of windward and leeward sides of slopes, valleys that can channel wind flow, vegetative windbreaks, and buildings that can affect air flow should be directed towards the consideration of these types of potential threats.

Topography and vegetation should also be considered when evaluating how a site is observed from outside its boundaries as well as how the surrounding area is observed from the site. Do these factors enhance observation of surrounding activities from the within the site while minimizing the views back to the building and site? Clear sight lines that allow security personnel and security devices to monitor the site and area beyond are desirable characteristics. The blocking of clear sight lines into the site by potential aggressors should be an important security consideration. Variations in topography can be both positive and negative. A building situated at a higher elevation than the surrounding area can provide security personnel with good views of the surrounding area, although clear sight lines back to critical building areas would need to be screened. In contrast, situating a building adjacent to an area or building at a higher elevation can create a situation that allows for unwanted surveillance. The modification of vegetation and topographical factors by the landscape architect can enhance their security value and even turn a negative situation into a positive security attribute.

Site Layout Design

In new construction, integrate the natural site characteristics with the placement of the building(s) and the other site features such as roads, parking areas, walks, and other site amenities. In addition to considering the size of the building(s)' footprint, constraints based on zoning requirements, easements, and other deed restrictions need to be taken into account.

Where multiple buildings need to be located on a site, high risk buildings can either be clustered together or dispersed throughout the site. A clustered layout concentrates people, property and operations in one area where the proximity of the buildings to each other increases the risk of collateral damage. A dispersed layout reduces the risk that an attack on one building will have an impact on the rest of the buildings and site. However, a clustered layout can maximize the stand-off distance from the perimeter creating a "defensible space" zone, reducing the number of access control and surveillance points. A dispersed layout creates a need for a more extensive and complex security system. The best approach would be to concentrate buildings with functional compatibility and similar levels of threat, locating higher risk targets away from lower risk targets to minimize possible collateral damage.

With increasing interest in benefiting from climate and lighting advantages that proper solar orientation can provide, the positioning of the building, its architectural design, and the related open space needs to be balanced with the need for enhanced security concerns. Inherently, the benefit from solar orientation is from increased glazing and other architectural light controlling elements. As these are major concerns in a blast event, it is important to orient the building in a way that maximizes the solar benefit but addresses the need for a maximum setback for these building façades.

Storm water management is also a consideration that can be addressed in a manner that is not only environmentally responsible but at the same time, enhances a building's security. A traditional approach to storm water management usually includes the installation of drain inlets, catch basins, manholes, and large drainage pipes with connections to the municipal system requiring a penetration of the site perimeter. The penetration of the site's secure perimeter by a large underground pipe presents a security concern and possible intrusion point. Other drainage structures on site provide access and concealment opportunities. To the extent possible, the related open space of a site can be designed in a manner that looks to reduce or eliminate the need for these drainage structures. The use of dry wells that allow storm water to be collected and then slowly percolate back into the ground can be considered. Maximizing the pervious surface is another approach. Pervious pavements (such as pervious concrete, pervious asphalt and unit pavers installed on a pervious base) can allow storm water to filter through and back into the ground. Planted areas allow storm water to directly percolate back into the ground. Where planted areas or pond areas are created to help manage storm water, they can also provide buffers to reinforce setback distance and contribute to an aesthetically pleasing environment.

Access—Vehicular and Pedestrian

A line of bollards separating a pedestrian sidewalk with a drop-off area and the roadway
A waterwall structure and bollards at the terminus of a

A line of bollards provide an effective vehicular barrier for drop off areas, restricting vehicles but allowing pedestrians to pass through unimpeded.

The terminus of a "T" intersection at the Convention Center in Salt Lake City is celebrated with this waterwall and bollards. They also provide protection against a vehicle that could accelerate to a high rate of speed and attempt to ram a car or truck through the entry of the building. "T" intersections require special attention because of the opportunity for a vehicle to accelerate over a long distance.

Closely tied to the establishment of an effective setback distance is the control of access and circulation, particularly of vehicles. For both pedestrians and vehicles, a balance needs to be struck between security concerns and the ability to enter the site without undue delay or impediments.

This starts with a study of how people will be arriving to the site and the surrounding street network. Where pedestrians are coming from will help determine where access points should be located, how many access points are necessary, and how many people they should be designed to handle. The size of the adjacent streets, volume of traffic and whether they are one way or support two way traffic helps determine the where vehicular access points should be located. The expected volume of vehicles entering the site will determine how many access points are required. After vehicle entry, requirements for circulation within the site and parking need to be considered.

Vehicular drop-off areas for children, visitors, or disabled should be carefully coordinated with the building design. By their nature, these areas need to be located in close proximity to the building entrance. They should be coordinated with the hardening of the building, with vehicles able to have relatively close access to the building façade and lobby.

In planning for vehicle restriction and the barriers that will be used to enforce those restrictions, it is important to consider the role velocity plays in determining a barrier's effectiveness. Reducing the speed of a vehicle has a much greater impact on its ability to ram and breakthrough a barrier than does limiting the size of the vehicle.

Long, straight vehicular approaches should be avoided as they provide an opportunity for a vehicle to accelerate to a high speed. This can be a serious security concern if these straight approaches are also perpendicular to the building, particularly a building entrance or other ground level treatment that would allow the vehicle to crash through protective barriers and penetrate the building envelope.

The speed of vehicles that have entered the site should be limited by the design of the vehicular circulation network. This can be done in a very direct way by strategically locating speed bumps (an abrupt change in pavement appropriate for low speeds) or speed humps (a more gentle change of elevation used to enforce a speed limit). The access road itself can be curvilinear, with traffic circles and/or small radius turns, limiting the speed of vehicles and at the same time creating the opportunity for a more interesting approach. Raised crosswalks function to slow vehicle speed as well as minimize the inherent pedestrian/vehicular conflict. This can create a more pedestrian friendly site environment, increasing safety and reducing liability. In order for any of these strategies to be effective there must be barriers to prevent vehicles from leaving the roadway and circumventing the efforts to restrict vehicular speed and circulation.

Loading docks should be located so that vehicles will not be allowed under the building, if possible, and if not, driveways under the building for vehicular traffic should be as limited as possible. If loading areas must be located under the building, they should be hardened to limit the effect of any blast event and structural damage to the building. Loading docks and shipping and receiving areas should be separated from utility rooms, utility mains, service entrances, including electrical, telephone, data, fire detection/alarm/suppression systems, cooling, heating, etc. by at least 50 feet (BIPS 06 / FEMA 426). Adequate signage clearly identifying truck circulation and delivery points should be provided so that trucks stay in their designated areas.

A well designed comprehensive signage system is important for visitors to find their way on a day to day basis. It eliminates confusion and keeps people away from restricted areas, preventing a possible loss of site security. Good wayfinding systems identify entrances and exits, allowable pedestrian and vehicular circulation routes, parking areas, delivery areas, and drop-off areas. They include cautionary signs for visitors and employees.

These same signs are important in emergencies, as they help first responders navigate through the site to their destinations as quickly as possible. While signage should identify areas where people can go, they should not (unless required by regulation) identify sensitive areas that are restricted.

All road design strategies to restrict vehicular speed need to take into account the need for access by emergency vehicles. While some strategies may delay emergency vehicle access, increasing response time, tight radius turns can actually prevent larger apparatus like fire trucks from being able to enter the site. Care needs to be taken in making sure that larger emergency (and even maintenance) vehicles can negotiate through the access roads without difficultly.

Parking

Parking structures can result in a more effective use of available open space but would have to be structurally hardened to increase their blast resistance. Underground parking, which may be the most economical approach, puts the building at greatest risk. Parking structures located under the building are highly vulnerable to attack by bomb laden vehicles and require a high level of security procedures to mitigate the threat. Wherever possible, it is best to place unsecured (high levels of visitors) or high risk areas (like parking) outside the building footprint, and locate critical assets inside the building.

With any parking structure, crime prevention techniques need to be integrated into the design. Visibility into and out of the parking structure is an important security factor. Stairs and elevators that service the parking area should be designed to be as open as possible so that people can see and be seen. Within the parking structure the design should provide for clear sightlines without concealed areas where someone might hide, so that people can make good decisions regarding their route to their cars, elevator, or stairs.

Surface parking areas should be located so as to keep potential threats away from a building or from the interior of a group of buildings. It should be a high priority to locate parking away from high risk buildings and in areas where it presents the least risk to personnel. Although the best location for surface parking is off-site, this is often not practical or feasible. Parking areas and vehicular circulation routes need to be restricted in order to provide adequate setbacks (consideration should be given to parking areas on adjacent sites and the ability to bring a car or truck within close proximity of the building being protected). Parking lots that are designed with one-way circulation provide more control and easier monitoring by security personnel. While providing appropriate setbacks, it is also important to locate parking within view of occupied buildings. Providing more "eyes on the street" can help identify and report suspicious activity, as well as providing enhanced security for those walking to the building or back to their cars in the parking lot (a basic CPTED principle for improving informal routine security). The parking area should be designed with adequate lighting levels, and CCTV cameras strategically located should be used where warranted to provide formal surveillance and monitoring.

Surface parking results in large paved areas that can contribute significantly to storm water runoff, and create security concerns. Therefore, consideration should be given to the use of pervious pavements (concrete and asphalt), open planted areas, and bioswales, to minimize the amount of surface runoff. For general safety, pedestrian/vehicular conflicts should be minimized by providing pedestrian walks and clearly delineated crosswalks. Here again, raised crosswalks can not only increase safety but also serve to control vehicle speed.

Security and Landscape Design

The goals and objectives of the client's requirements, stewardship of the natural and built environment and enhanced security need to be integrated into a comprehensive design solution. Landscape architects are very familiar with the principles and techniques that can be implemented to create designs that are environmentally sensitive, conserve resources, relate to the context of the surroundings, establish unique identity and sense of place, address cultural and social issues, achieve a human scale, and marry form and function, all in an aesthetically pleasing approach. The implementation of good design principles and security requirements are not mutually exclusive.

A variety of site features and amenities from the landscape architectural palette can be used to provide the required level of security. The manipulation of landforms, integration of water features, raised planters, vegetation, changes in elevation of paved areas, fences, a wide range of street furniture, site elements and amenities (bollards, benches, flagpoles, kiosks, etc) can all be strategically implemented to enhance security. These site design features can be used to restrict and control pedestrian and vehicular circulation and access as well as prevent unwanted surveillance. They must be carefully located as to not impede pedestrian access to public entrances, disrupt the flow of pedestrian traffic along the sidewalk, or prevent access by emergency vehicles. Their creative use can result in spaces that are responsive to the needs of the people that use them, creating active public spaces overflowing with positive activity. This level of positive activity brings with it an inherent safety and security in the form of informal surveillance and makes undesirable activity stand out in a much more obvious way.

The various designs available in site amenities provide the opportunity for the site to be an extension of the building architecture, in keeping with the context and character of the area. By employing the basic principles of design such as:

  • unity (the repetition of a limited number of elements),
  • harmony (the elements that are used to create unity must go together),
  • emphasis (giving added importance to certain elements),
  • balance (the overall balance of weight and mass of site elements in a symmetrical, asymmetrical, regular, or irregular arrangement),
  • scale (the relationship of the size of the site elements and the pedestrian or user), and
  • rhythm (the sequencing of site elements)

the various site elements can be woven together to form a rich urban fabric. Streetscapes can be created that enhance the pedestrian experience and provide perimeter security that is virtually seamless and transparent.

Bollards and boulders outside the American Indian Museum, Washington, DC
Raised planters as vehicle barriers outside the American Indian Museum, Washington, DC

The American Indian Museum in the Washington, D.C, combines bollards with boulders to prevent vehicular access. The boulders become an extension of the museum itself.

The raised planters in conjunction with the bollards and boulders restrict vehicular access. The plantings are meaningful and significant to the message of the museum.

Stand-off Distance

Distance is the most cost-effective approach to mitigating the effects of blast. Stand-off distance is defined as the distance between an asset and the potential threat. The effects of blast are based on the type of explosive threat and the construction and design of the asset in addition to distance. This combination of factors determines the level of protection. Based on that principle, it is best to maximize stand-off distance. Every foot counts, even if the desired level of protection cannot be achieved through stand-off distance alone. In circumstances where the ability to provide stand-off distance is limited, complementary modifications to the building should be considered to harden the structure to meet the desired level of protection. (See also Effective Site Security Design and Site Security Design Process)

Graphic showing the most effective wat to deal with the theat of an explosive blast with a stand-off zone: a depiction of the Assest (a house), the Stand-off Zone (an arrow), and the blast (a red burst)

The most effective approach to deal with the threat of explosive blast is to create a "stand-off distance" between the asset being protected and an area that a bomb laden vehicle can access.
Photo Courtesy of FEMA 426, Source: U.S. Air Force, Installation Force Protection Guide

In establishing stand-off distance, the first level of protection created is referred to as the "keep out zone". By definition it establishes a minimum guaranteed distance between a bomb laden vehicle and the asset being protected by establishing a continuous line of perimeter barriers that cannot be breached by ramming. In an effort to maximize the stand-off distance, the keep out zone is generally considered to extend out to the site perimeter. However, in urban situations where space limitations exist, it is possible to extend the keep out zone by installing barriers along the curb line, eliminating curbside parking, and, if determined necessary, even closing the street to regular traffic. Efforts to establish a keep out zone that extends beyond the property line would require the cooperation, coordination and approval of local authorities. Another way to create a setback on a narrow site is to adjust a building's massing so that the upper floors of the building "step away" from the street, or shift the most important functions to areas that will be less exposed should a bomb blast occur on the street level.

Exterior view of the EPA Region 8 Headquarters in Denver CO
North facade and view of upper curtain wall of the EPA Region 8 Headquarters in Denver CO with access to public transportation integrated into the building design
The pedestrian avenue with a bus passing by in front of the EPA Region 8 Headquarters in Denver CO

EPA Region 8 Headquarters in Denver, Colorado steps back from the street for security, while still integrating into the pedestrian oriented LoDo District which is also connected to public transportation.

A "clear zone" is an area immediately adjacent to the building that is free of any visual obstructions. This permits unimpeded monitoring of all activity within the clear zone. In addition a clear zone should ideally be maintained on both sides of the perimeter to provide an unobstructed view of the barrier and ground adjacent to it. A clear zone of 20 feet or more should exist between the perimeter barrier and exterior structures, parking areas, and other natural or manmade features. A clear zone of 50 feet or more should exist between the perimeter barrier and structures within the protected area, except where the perimeter wall constitutes part of the physical barrier. Barriers should be inspected and maintained to prevent compromise.

Bollards along the front entrance to the Federal Courthouse, Minneapolis MN
Plaza area of the Federal Courthouse, Minneapolis, MN featuring green turf berms and bollard-type seating elements

The Federal Courthouse in Minneapolis prevents vehicular access using bollards along the front of the entrance.

Green turf berms prevent objects from being concealed, along with seating elements, which rise in the plaza to prevent vehicles access to the plaza area.

Vehicle circulation, parking, and maintenance areas should be located away from critical building components, or these components need to be adequately hardened. These critical building components include emergency building systems, communication distribution centers, fire control systems, and stair, elevator, and utility shafts.

Controlled access zones limit access through the perimeter security to the area immediately surrounding the building. Access can be controlled by the installation of physical barriers. Access control can provide a range of levels of control: complete "full control" of the perimeter from entry by vehicles and pedestrians; restriction of vehicles but full pedestrian access; and/or electronic monitoring of the site perimeter. Entry into a controlled access zone should only be through an entry control point. An exclusive zone establishes an area where anyone entering must have a purpose related to the building. A non-exclusive zone is one where the public has access or a right-of-way.

Physical Protective Barriers

Physical protective barriers can help restrict, channel, or impede access, and constitute a continuous barrier around the site. In addition to its physical effectiveness, a protective barrier can also create a psychological deterrent to anyone planning an unauthorized entry.

Physical protective barriers can be natural or manmade. Some of these natural barriers include water features, changes in topography, use of vegetation, and creating rough terrain that would be difficult to traverse. Some manmade elements that are a part of site vocabulary include fences, walls, planters, bollards, fountains, site furniture, and amenities.

Two pedestrians walking along a wide path with a heavily raised planted berm on the left side to protect the courthouse beyond
A wide sloping walkway with raised planted berms on each side and a single bollard at the end to prevent cars from driving on it
A wide sloping walkway with raised planted berms on each side

The Hennepin County Courthouse in Minneapolis uses a heavily planted berm to prevent vehicles from entering a stand-off zone.

A single bollard prevents vehicles from driving down the walkway, the raised planted berms to each side provide the balance of the required vehicular restriction.

The berms prevent vehicles from gaining access to the central courtyard and close proximity to the building.

When considering the implementation of any perimeter security barrier it is important to investigate any below ground conditions that may exist. In some cases there may be basements that extend out below the sidewalk. Particularly in urban areas, there may be underground utilities (these may resemble a bowl of spaghetti). Subway lines, tunnels, underground parking, and other below ground uses need to be identified.

Of special note for care and concern is the protection of any trees, particularly street trees. Many of the perimeter security elements require either much larger footings or installation in grade beams in order to be effective. This can have a detrimental effect on the root system of a tree. Street trees in an urban environment have a tough enough time surviving these adverse conditions without additional encroachment on their limited access to water, soil, air, and nutrients. Therefore, the implementation of a perimeter security strategy should include measures to compensate for any negative effects on existing trees and holistically include measures that integrate the planting of new trees to ensure their survival. A thriving street tree is another perimeter security element whose value as a physical barrier and an element that enhances the streetscape and pedestrian experience, should not be dismissed.

Temporary or semi-permanent barriers are measures that can be implemented when threat levels increase. These measures include blocking access with heavy objects and vehicles to create a controlled access area. Additional security posts and personnel, along with temporary fencing, can allow the screening of pedestrians to ensure entry with proper credentials. These measures should not be considered a long-term or permanent security design.

Fencing is one of the most common elements used to protect a controlled area. The type of fencing is determined by threat and degree of permanence. Fencing provides a strong psychological deterrent but has proven to provide only a limited entry delay to motivated aggressors. The more formidable the barrier the longer the unauthorized entry delay. Types of fencing range from chain link and anti-climb, to barbed wire and steel cable (often used in conjunction with other fence types to provide additional crash resistance). A top guard consisting of barbed wire or tape facing outward and upward at a 45 degree angle can be added to perimeter fences and interior enclosures; however liability issues must be considered. Fencing can be augmented with motion sensors and CCTV cameras making the barrier more effective and intruders easier to detect.

Brick or masonry walls seven feet high with a top guard can provide a high level of perimeter security. A wall can also reduce pressure levels experienced by the building in a blast event. It can limit observation of activities from the unprotected side of the wall. A high solid wall, while providing security advantages, can be a bit overbearing in some situations, particularly in more urban areas. An alternative to consider is a lower wall with a fence attached to the top. This can be an effective solution to address both anti-ram and observation concerns.

Anti-ram vehicle barriers prevent vehicle access for pedestrian protection and building security. Passive barriers are stationary or fixed site elements that are used to create perimeter or edge protection. Active barriers can be retracted or moved out of the way to create controlled vehicle entry points.

Passive Vehicle Barriers

Sculptural bollards with people seated on them and pedestrains walking past in the Wall Street financial district
A low walled box along a curb to restrict vehicles featuring large stones and a bronze sculpture

Bollards can be creatively designed to provide vehicular restriction, like these sculptural pieces on Broadway preventing vehicles from entering the Wall Street Financial District.

A low wall along the curb line does not always need to be a planter to restrict vehicles. It can be a frame for art and used in conjunction with planters, bus shelters and other street amenities.

Bollards can be as simple as a concrete filled steel pipe or as elaborate as cast stone. They can be set along the curb, or lined along the property line, or in creative layouts in conjunction with other site elements. They can be set in large concrete footings or embedded in a continuous grade beam set several feet below the ground. In order to be effective they should have an overall height of at least 40 inches high to be higher than a vehicle bumper. The spacing of the bollards should have a minimum clear distance between them of at least 3 feet in order to meet the requirements of the Americans with Disabilities Act (ADA) but no more than 5 feet to respond to the minimum width of a vehicle.

A plinth (base of a platform) or a raised, reinforced planter wall that is placed as close as possible to the curb, are other possible passive barriers. If they are built beyond the property line, it is necessary to coordinate their construction with local jurisdictional authorities. The walls must extend beneath the grade; thus, existing below ground site conditions need to be considered. If curbside parking is allowed, at least 18 inches of space is needed to open a vehicle door. The wall must contain breaks to provide spaces for pedestrians crossing the street to access the sidewalk. However, according to the SDDCTEA Pamphlet 55-17 Better Military Traffic Engineering and MUTCD/AASHTO Roadside Design Guide they should be at least 24".

Surface mounted planters can also be used to provide perimeter security. These individual planters can be mounted directly on a sidewalk. They resist impact through inertia and friction between planter and sidewalk. Their displacement can be reduced by installing the planter below the pavement surface or by installing an inner ram-resistance bollard.

Active Vehicle Barriers

Rising plate vehicle barriers in the center flanked by decorative bollards
Vehicle entry gate with a crash beam in a semi-raised position and two concrete anchors on each side displaying stop signs

A rising plate vehicular barrier in conjunction with decorative bollards and a low stone wall provide deterrence of unauthorized vehicles at this entry to the rear of the U.S. Capitol.

A crash beam has a steel tensioned cable that locks down between the two large concrete anchors on each side, to effectively stop a vehicle.

Active vehicle barriers include site elements such as crash beams, crash gates, retractable bollards, surface mounted plate systems, rotating wedge systems, and GRAB® barriers. They all require some activation by security personnel at entry points to control vehicle access or operated by automated access control technology.

In cases where the highest level of security is required, particularly where buildings require 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 and may also be utilized at sites other than the "highest" level of security.

The rising vehicular plate barrier is one of the most common of the elements designed to control vehicular entry. It can be installed as a flush mount onto existing pavements or as part of a shallow foundation system. This heavy-duty steel barrier rises in a matter of seconds to form a triangular shaped form, hinged at ground level on the protected side. It can be designed to stop a five- or six-ton vehicle traveling 50 miles per hour dead in its tracks and still remain operational. Very similar in operation is the rotating wedge barrier. Cylindrical in shape, it rotates out of the ground to provide a formidable barrier to an oncoming car or truck that can attain the highest impact ratings. This type of barrier can be visually problematic if it is not integrated with the other related site elements. Thought should be given to the area leading to and immediately adjacent to the barrier to keep the barrier from becoming the dominant element of the site security strategies.

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. However, the significant difference is that the hydraulically powered arm locks down between two crash rated anchors. What provides its deceptively high strength and high impact rating is the steel cable beam integrated into the arm. The steel cable locked between the heavy anchors on each side creates a highly effective vehicular barrier. Crash gates use a similar system of steel cables along the face of the gate that lock into anchors. This increases the impact rating for whatever fence is being used (chain link, tubular steel, solid steel). Keep in mind that their slower operating speed compared to other active barriers may result in tailgating vulnerability.

Retractable bollards can also be used to control vehicular entry. These bollards lower flush to the ground to allow vehicles to pass, but raise up to prevent vehicular entry. They can be operated with a hydraulic, pneumatic or manual system. The manually operated bollards are counter balanced for ease of operation and can be locked in an up or retracted position. They are usually grouped and spaced between 3 and 4 feet on center when used for vehicular control and can be operated individually or as a group. They come in a variety of styles that can complement the existing context and architecture. As with passive bollards, they have the advantage of allowing pedestrians to pass through unimpeded, while still restricting vehicular access unless lowered. A common concern regarding retractable bollards is the potential for accidental deployment, creating a liability issue. This can be mitigated by utilization of a "sliding bollard system."

Where a street or other straight portion of road exists that would allow a vehicle room to accelerate to high speeds, it is advisable to design the vehicular entry way with elements that force a vehicle to slow down and turn before reaching the vehicular entry barrier.

Entrance gate with a rotating wedge vehicle barrier displaying the word stop
An open entry gate with pedestrians walking along a path between trees set in low walls and among bollards

A rotating wedge vehicular barrier provides the real stopping power at this entrance gate to New York City's City Hall.

The security elements that were incorporated into the redesign of City Hall Park in the 1990's allowed the Park to be secured in a matter of minutes by the regular security force, simply by closing the gates.

Location Selection for Vehicle Access and Entry Control

The first step for locating a vehicle access and entry control point is to evaluate anticipated demand. It is important to analyze traffic patterns, road network capabilities, and vehicle capacity. In urban environments, this analysis can help determine where logical vehicle access and entry control points, for both vehicles and pedestrians, can be most effectively located. For more open areas, consider existing terrain, with flat terrain or a gentle rise up to the entry point with a clear view of arriving vehicles being ideal.

Consider existing natural site features, such as topography, water features, dense tree stands and how they can help keep vehicles from leaving the roadway and bypassing the entry control point. Whether utilizing natural or manmade barriers, a vehicle should not be allowed the opportunity to circumvent the entry control point.

Some Design Considerations for Vehicle Access and Entry Control

It is a good practice to provide traffic obstacles near entry points to slow traffic down. Another strategy is to offset vehicle entrances from the direction of a vehicle's approach to force a reduction in speed. A security design should try to minimize the number of access roads and entrances to a site (some entrances can be closed and secured during non-peak periods). Designated entry for commercial, service and delivery vehicles should be designed away from high risk buildings. Design entry points to allow adequate assessment of authorization of approaching vehicles, while maintaining the safety of gate guards and other vehicles approaching the entry point and without disrupting pedestrian or traffic flow. This may require an area for traffic queuing on the street that leaves the sidewalk open for pedestrian traffic flow.

A pull-over lane to check suspect vehicles should be provided. This area should allow other authorized vehicles to continue to access the site. Design inspection areas that are not visible to the public and allow for inspection of the undercarriage and top of vehicles. A vehicle access control point should provide a final denial barrier that will stop unauthorized vehicles from entering the site. The vehicular access control point should include the design of a barrier system to impede both inbound and outbound vehicles.

Physical Security Lighting

Although lighting alone does not inherently improve security, it is an important component in an overall site security plan. It allows security personnel to maintain critical visual monitoring of the site. Security lighting provides both a physical and psychological deterrent.

At entry control points, lighting should give drivers a clear view of the gatehouse and security personnel a clear view of approaching drivers and vehicles. High mast lighting is generally recommended because of its broader and more natural light distribution. However, concerns regarding light pollution need to be taken into account and this type of lighting may not be the best choice. A minimum surface lighting average of 4 horizontal foot-candles are needed to provide adequate lighting at entry control points (BIPS 06 / FEMA 426).

Types of Lighting

There are several different types of lighting and lighting strategies that can be employed. The overall requirements of the building and unique characteristics of the site need to be evaluated in order to determine the best lighting type or combination of lighting types.

Continuous lighting is the most common security lighting system which consists of fixed lights arranged to flood an area continuously during darkness with overlapping cones of light to the desired illumination level. There are two basic continuous security lighting strategies. The first is the glare projection security lighting method. This method lights the area with high-intensity lighting, making an intruder highly visible while making it difficult to see inside the secure area, keeping guards and security personnel in relative darkness. Because of the high light levels directed towards the perimeter of the site, concerns regarding light pollution need to be considered.

The second is the controlled security lighting method. This method adjusts the width of the lighted strip to fit the particular need, limiting the lighted areas outside the perimeter. This lighting may either illuminate or silhouette the security personnel. It is a much more directed approach than the glare projection method and can be better suited to entry control points that are in close proximity of other buildings or residential areas.

A standby security lighting system consists of lights that are not continuously lit. This system's lights are turned on either automatically (activated by sensors) or manually when suspicious activity is detected. A movable security lighting system consists of manually operated, movable searchlights that may be lit during hours of darkness or as needed. Movable lighting is not effective as a standalone system and is usually used to supplement a continuous or standby security lighting system.

An emergency lighting system is a backup power system that may duplicate any or all of the lighting types should an event cause the main lighting systems to become inoperative. In order to be effective during these periods of emergency, the system must use alternative power sources such as generators or batteries.

Site Utilities

Utility systems can suffer significant damage from an explosion that can create serious life safety issues for the building occupants. Perhaps even more than the physical damage to the structure of the building itself, critical utility damage can threaten the immediate safety of the building occupants as well as make their evacuation of the building difficult or impossible. To minimize potential damage to critical utilities, the landscape architect needs to carefully consider their locations and routing.

Whenever possible, utilities should be placed underground or alternatively concealed and protected. The interface between the utilities at the site perimeter should be evaluated as this area of public access can be a particularly vulnerable point. Unless required, signage should not identify the locations of critical utilities. If there is a requirement for storage of hazardous materials (petroleum, gasoline, other chemicals that could be harmful to a building or its occupants), these tanks should be located downslope and a minimum of 100 feet from all buildings (BIPS 06 / FEMA 426). Trash receptacles (a concealed place that can be used to hide explosives), should be placed at least 30 feet away from the building. Parking areas and vehicle circulation routes should be laid out in a way that keeps them at least 50 feet from critical utility systems.

Storm water management techniques that retain storm water on site are generally considered for their environmental impact. However, storm water management can also enhance site security. By designing a storm water management system that retains storm water on site, the connection to off-site storm water systems can be eliminated or significantly reduced in size. As storm water drain pipes are generally the largest utility perimeter site penetration, it potentially could allow access to an intruder through these large diameter pipes. The elimination of this perimeter site penetration or its reduction in size, takes away this potential access.

All utility penetration of a site's perimeter barrier should be sealed or secured to eliminate openings large enough to pass through the barrier. If access is required for maintenance of utilities, secure all penetrations so that openings do not allow intruder access. Access points such as manholes or drainage structure grates larger than 10" in diameter should be secured by lock and hasp, welding or bolting to their frame (BIPS 06 / FEMA 426).

Utilities, or other openings that pass through a secure perimeter, that have a cross-sectional area greater than 96 inches and whose smallest dimension is greater than 6 inches should be protected by securely fastened bar grills across the opening or as an alternative, substitute with an equivalent number of multiple pipes having an individual diameter of 10 inches or less. As these measures may have an impact on the utility's effectiveness and performance ensure that any security measures are coordinated with the engineers to compensate for any reductions in flow capacity or maintenance requirements. If a very high level of security is warranted, the consideration of intrusion detection sensors and overt or covert visual surveillance systems for utilities can be considered.

Additional Resources

WBDG

Building Types

Ammunition and Explosive Storage Magazines, Armories, Federal Courthouse, Land Port of Entry, Government Laboratory, Parking Facilities, Office Building

Space Types

Parking: Basement, Parking: Outside / Structured, Parking: Surface, Plaza

Design Disciplines

Applicable to Design Disciplines

Design Objectives

Aesthetics—Understanding the Language and Elements of Design, Aesthetics—Engage the Integrated Design Process, Cost-Effective Branch, Secure / Safe—Fire Protection, Secure / Safe—Occupant Safety and Health, Secure / Safe—Security for Building Occupants and Assets, Sustainable—Optimize Site Potential

Organizations

Publications