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The barrier may be along the site property line or, within a large site or campus, placed independently of the property line. When along the prop - erty line, the barrier forms the interface between public and private space, and thus, in an urban setting, it may have major visual and functional i\ m - pacts on city amenities. If the barrier is within the site, it may have \ a major impact on the visual appeal of the site and the experience of the ap - proach to the building.

A perimeter security design involves two main elements: the perimeter barrier that prevents unauthorized vehicles and pedestrians from en - tering the site, and access control points at which vehicles and pedestrians can be screened and, if necessary, inspected before they pass through the barrier. Barrier system design and types of barriers are described in this chapter. Access control points are described in Chapter 5, Section 5.3, and Chapter 6, Section 6.5, for open and urban sites, respectively.

The following are suggested as some of the goals of perimeter security planning:

m To provide an appropriate balance between the need to accommodate perimeter security for sensitive buildings and their occupants, and the need to maintain the vitality of the public realm. m To provide security in the context of streetscape enhancement and public realm beautification, rather than as a separate or redundant system of components whose only purpose is security. * Perimeter security design 4-2 m To expand the palette of elements that can gracefully or unobtrusively provide perimeter security in a manner that does not clutter the public realm, while avoiding the monotony of endless lines of jersey barriers or bollards which only evoke defensiveness (see Section 4.6.2 for an example of an innovative unobtrusive security element). m To produce a coherent strategy for deploying specific families of streetscape and security elements in which priority is given to achieving aesthetic continuity along streets, rather than solutions selected solely by the needs of a particular building under the jurisdiction of one owner or agency. m To provide perimeter security in a manner that does not impede the city’s commerce and vitality , nor excessively restrict or impede operational use of sidewalks or pedestrian and vehicular mobility, or impact the health of existing trees. Perimeter protection may participate in all three layers of defense.

The first layer applies when the access control is outside the propert\ y line. The second layer applies when there is controlled access around a building within the property line. The third layer applies to under - ground parking, or parking underneath a plaza (see Chapter 6, Section 6.4). It also applies when the access control is at the building face.

Perimeter security protection is accomplished by design strategies that \ use a variety of methods to protect the site. The two following sections\ provide some broad guidelines for the design of barrier systems and de - tails of the characteristics of barriers currently in use.

4.2 BArrier system design 4.2.1 issues Of B Arrier systems design t he architecture and the landscaping of the site entry elements are the first part (and may be the only part) of the project that is\ visible. As such, they introduce the identity of the site and its ar - chitectural style and quality, and impart a sense of welcome or “stay away” (Figure 4-1).

Sidewalks should be open and accessible to pedestrians to the greatest e\ x - tent possible, and security elements should not interfere with circulation, particularly in crowded locations. Perimeter security design 4-3 Issues to be considered in the design of the barrier system include:

m To ensure protection to the desired level, the design and selection of barriers should be based directly on the design base threat assessed for\ the project, as well as available countermeasures and their ability to mitigate risk. m The barrier layout at sidewalks should be such that a constant clear path of 8 feet or 50% of the sidewalk, whichever is the greater, should be maintained. m For buildings with a yard, security elements should be placed in or at the edge of the yard depending on available space and stand-off. m All necessary security elements should be installed to minimize obstruction of the clear path. If it is necessary for space reasons to place elements at the curb they should be placed in an available amenity strip adjacent to most curbs, since this space is already designated for stree\ t furniture and trees and is not part of the existing clear path. m Any security (or other) object placed on the curb should be at least two feet from the curb line to allow for door opening and to facilitate passenger vehicle pick-up and drop-offs, if this can be done anywhere along the curb. However, the most effective placement is at a maximum of two feet: this allows the barrier to engage the engine block and mass of an approaching vehicle before the tires have impacted the curb and begun to launch it over the barrier. Ideally, drop-off points should be located in pull-over or stopping points where the setback is greatest. At a distance of more than two feet, the curb can become a major factor in barrier height requirements and in reducing their effectiveness. Figure 4-1: c ustom bollards match the architecture at a defended corner. Perimeter security design 4-4 m A bollard barrier system is less intrusive if it is short in length and thoughtfully integrated into the entire perimeter security system. The bollard materials should harmonize with the building architecture. Figure 4-2 shows a small row of bollards protecting a building entrance.\ The custom-designed stainless steel bollards harmonize well with the building architecture.

m Monotonous repetition of a single element should be avoided. Block after block of the same element, no matter how attractive, does not create good design (Figures 4-3 and 4-4). When a continuous line of bollards approaches 100 feet, they should be interspersed with other streetscape elements, such as hardened benches, planters, or trees. Figure 4-2: stainless steel covers on bollards harmonize with the building entrance. Figure 4-3: m onotonous repetition of bollards Perimeter security design 4-5 m Hydraulic barriers, drop arm beams and the complete system including security gatehouses are visually intrusive. Wherever possible, such entr\ y controls should be located in access roads and service alleys. m The use of a combination of barrier types establishes a flexible desig\ n palette that responds to security requirements in accordance with diverse perimeter conditions (Figure 4-5). Figure 4-4: these bollards resemble a wall.

sOurce: ncPc) Figure 4-5: top: combination of low retaining walls and low bollards.

Bottom, left: combination of oversize bollard and large planters placed on very wide sidewalk. Bottom, right: combination of tree and bollards. Perimeter security design 4-6 Opportunities to add a palette of elements, such as varied bollard types\ , engineered sculptured forms, hardened street furniture, low walls, and judicious landscaping can all assist in creating a functional yet attractive barrier that will enhance the setting. Solutions that integrate a number\ of appropriate perimeter barriers into the overall site design will be more successful (Figure 4-6).

The graphic box following shows varied bollard sizes combined with other\ elements to reduce the monotony of a long curbside barrier system. Figure 4-6: A combination of barrier types for a variety of threat conditions. Vehicle access to this building is prevented by custom designed bollards, a sculptured concrete barrier, fences and trees sOurce: design: deLLA VALLe + BernHeimer ArcHitects BOLLARD VARIATIONS AS PART OF THE STREETSCAPE small and large bollards, trees and plants. in a few years the trees will dominate the streetscape (right).

Bollards, trees, and lamp standards (below). Perimeter security design 4-7 m The placement of barriers at corners, driveways, sally ports, stairs, an\ d handicapped ramps requires careful attention. m Barriers at the edges of soil slopes need to be investigated carefully.

m Corners need creative design, for example, to increase the area to account for pedestrian queuing while interspersing effective barriers that can consist of non-obvious objects, such as traffic signals, signs, lighting, etc. In addition, corners can offer the opportunity to consider barrier design in depth to facilitate pedestrian flow and protection while preventing vehicle entry. Space for several functions are important consid - erations: (1) pedestrians to circulate during the green signal phase, (2) a pedestrian holding area during the red signal phase, (3) vehicles turning the corner, and (4) people joining in the queue at the red signal phase. These space requirements demand that sidewalk corners be kept clear of obstructions. Reduction of corner spac\ e can lead to people using the roadbed as a waiting area. Sidewalk corners (defined as the space created by extending lines to the edge of the s\ ide - walk) should be free of objects. No part of a corner curb cut should ha\ ve any security elements. Wrap-around corners (stretches from the edge of one curb cut to the edge of the adjacent one) at rounded sidewalk cor - ners should not be permitted.

m Emergency evacuation and access are important considerations.

The primary goal of perimeter security is to provide facilities with a layer of barrier protection. However, the same protection that keeps dangerous vehicles or people away could also keep first responders from approaching the building quickly and enabling people to exit rapidly. m Landscape materials can soften and naturalize the appearance of many types of constructed barriers, improving their appearance and compatibility with the surrounding areas (Figure 4-7). m When possible, position gates and perimeter boundary fences outside the blast vulnerability envelope. m For high-risk buildings, barriers should be provided at site and building entries. Vehicles should not be permitted to park next to the perimeter walls of the secured area. corners can be vulnerable points for vehicle bomb attacks. they are often the area of greatest approach speed, greatest number of approach avenues, and most perpendicular impact. unless they are carefully designed to impede bomb-laden vehicles, it may be possible for an attacker to drive onto the sidewalk and proceed unimpeded to an intended target. Perimeter security design 4-8 m In case of an elevated risk, vehicles can be used as very temporary physical barriers when placed in front of buildings or across access roads, but they are very detrimental to the character of an entry when used as a long-term risk mitigation measure. Case Study 5 describes a large agency complex in Washington, D.C., that features an arcaded crescent that wraps around two sides of the building and encloses an internal garden space. This creative security barrier makes a positive contribution to the urban environment. Figure 4-7: Low and high walls softened with landscaping. CASE STUDY 5: A MAJOR GOVERNMENT BUILDING 1.0 INTRODUCTION this new government building using innovative security barriers is located at the intersection of two major streets in a city’s industrial area that is undergoing urban renewal. the complex is designed to engage the street edges, with an entrance across from a nearby transit center. retail facilities border to the east, while a trellised garden wall to the south animates the street edges in addition to enhancing the perimeter security. Perimeter security design 4-9 CASE STUDY 5: A MAJOR GOVERNMENT BUILDING (continued) 1.1 Project Scope the building program includes general office space, training rooms, lab\ oratories, a library, an auditorium, underground parking, and auxiliary services. A three-story, planted, arcaded crescent wraps around the north and west boundaries, enclosing an internal garden space. Loading docks and an inspection booth are integrated into the architecture and garden \ walls.

1.2 Project Team moshe safdie and Associates with OPX Architecture, Associate Architects 1.3 Project Schedule completed in 2007 2.0 DESIGN APPROACH 2.1 Issues Addressed m security needs of a major government building m Limited space in existing urban context 2.2 Security Strategy First Layer of Defense m unusual perimeter arcade, which provides attractive, integrated security m entry controls and screening Second Layer of Defense m Walls with attractive security fencing Third Layer of Defense m Building architecture incorporates risk mitigation measures 3.0 BLENDING WITH THE NEIGHBORHOOD CONTEXT m nice transition from neighborhood low-rise buildings m Arcade and landscaped plaza adds amenity 4.0 INNOVATIONS AND BEST PRACTICES m A mix of barriers and deterrents designed within the context of the site\ and its surroundings provides multiple layers of protection and creates an amenity for the ne\ ighborhood m secur ity is part of the aesthetic of the architectural design, an integral component, i\ nstead of an aftertho ught Perimeter security design 4-10 4.2.2 BArrier crAsh test st AndArds There is a wide variety of design methods and devices that can be used t\ o provide protection. The site risk analysis (see Chapter 2) will provid\ e in - formation on the nature of the threat to be mitigated, and the designer needs to know the relative performance of the methods that are available so that appropriate choices can be made for the various conditions that will be encountered. Since this publication is primarily concerned with protecting buildings from bomb-carrying vehicles, effectiveness in stop - ping vehicle entry is a critical performance parameter.

The crash testing standard in common use was developed by the Department of State (DOS). To obtain DOS certification, the vehicle bar - rier must be tested by an independent crash test facility to meet DOS standards. The test specifies perpendicular barrier impact by a 15,000\ -lb.

(6810 kg.) diesel truck.

Initially, the DOS standard provided for three levels of intrusion:

m Level 3: Allows intrusion of the vehicle 36 inches (0.91 m) into the barrier m Level 2: Allows intrusion of the vehicle 20 feet (6.1 m) into the barrier m Level 1: Allows intrusion of the vehicle 50 feet (15.2 m) into the barrier In February 2003, the standard was revised, and levels 1 and 2 were de - leted. The standard currently provides certification for three classes\ of protection: Certification Class Speed (mph) Speed (kph) K12 50 mph 80 kph K8 40 mph 65 kph K4 30 mph 48 kph To become certified with a DOS “K” rating, the 15,000-lb. vehicle\ must achieve one of the K-rating speeds, and the bed of the truck must not penetrate the barrier by more than 36 inches. The test vehicle is a me - dium-duty truck such as those that any driver with a commercial license and a credit card can buy or rent. Note that the amount of intrusion is measured to the front of the cargo bed of the truck, where explosives would typically be located (Figure 4-8). Perimeter security design 4-11 This limited penetration is appropriate for the DOS because their facilities have usually been located in high-density areas with little or no set - back. In open sites with more adequate setback, deeper penetration may be acceptable, and agen - cies, such as the DoD or the DOE, or the private sector, may reinstate deeper penetration levels in the new ASTM standard under development (see below). Where the setback is extremely limited, every foot of penetration is critical.

The lack of a universally accepted testing and certification process f\ or bar - riers has hindered the development of components that are uniquely designed and appropriate for well-planned streetscapes. Typical testing methods today include a computer simulation, using finite-element anal\ ysis, followed by an actual crash test at a controlled facility. Computer simulations can help refine design details and reduce overall costs. However, the live crash tests are generally needed to verify the performance of the barrier.

Oftentimes, security projects are designed under tight deadlines with li\ m - ited budgets, so that few tested barriers are readily available. The result is that only a limited number of “off-the-shelf” items, such as bollards and concrete barriers, are available, and they may not be appropriate for ev\ ery location. To prevent such occurrences, the design effort in a major project should include time and money for the design and testing of custom pe - rimeter security elements in the early stages of the planning process.

A key aspect of testing an element is the availability of a proper stand\ ard by which to measure its effectiveness. Until recently, the general standard used was one created by the Department of State for overseas locations, utilized for domestic purposes. The standard does not provide for much flexibility in design. To address this, ASTM International has developed recent experience has shown that terrorists are making increasing use of a “double tap” tactic in which the first vehicle is intended to breach the barrier so that a second vehicle can pass through and get close to the building. careful design and control is necessary to prevent the first or second vehicle from entering the setback area. Figure 4-8: Barrier test intrusion limit. Perimeter security design 4-12 a new standard ( WK 2534, Standard Test Method for Vehicle Crash Testing of Perimeter Barriers and Gates ) to expand upon the DOS crash test standard. To meet the diverse needs of the various groups that will use the new ant\ i- ram standard, the types of test vehicles and test conditions included in the standard need to be expanded, and longer stopping distances will be re - instated for use on open sites where more space is available for greater stand-off distance.

The new standard will include additional vehicle sizes. The smallest will be a uni-body sedan that might be able to slip between bollards that would stop a larger and heavier vehicle, such as a single-unit truck or tractor-trailer. Another vehicle to be considered in the standard is a 3/4-ton (2000 kg) pickup truck. The largest vehicle will be a 60,000-l\ b.

(27 metric ton) tractor-trailer or dump truck, which would test the limits of the barrier.

4.2.3 determining BArrier design criteriA The security design criteria required for a barrier are largely deter - mined by key information obtained in the following steps in the risk assessment process:

1. Threat analysis should provide the following Design Basis Threat (see Chapter 2, Section 2.2.2, Step 1 of the FEMA Risk Assessment Steps) : m Vehicle size, weight, speed.

m Bomb size (weapon yield in pounds of TNT equivalent) and worst-case stand-off distance. 2. Vulnerability analysis provides: m Building envelope and structural information that contribute to the determination of the appropriate stand-off distance, and that enable possible tradeoff between alternative building characteristics and stand-off distances to be evaluated and costed. m Information on available stand-off distances.

m Information on the possible reduction of vehicle speed through the existing or modified characteristics of approach roads. m Limitations imposed by underground utilities.

m Information on the types of soil, which affect barrier standards. Other criteria relating to planning, architectural, and streetscape issues are discussed in the following sections. Perimeter security design 4-13 4.3 BArrier mA teriALs And types 4.3.1 mAteriALs t here are four commonly used building materials for perimeter bar - riers: steel, cast iron, reinforced concrete, and cast stone. Natural materials such as rocks, trees, plants and earth forms may also be incorporated in a barrier system.

m Steel or cast iron can be used in almost any design and are usually easier to install than other materials. They are very strong and, compared to concrete, permit a smaller barrier to stop a vehicle. Steel and cast-iron barriers require more maintenance than other materials, such as concrete, and routine painting is necessary to prevent rust. m Reinforced concrete barriers take more time and manpower to install, but require little maintenance and are typically less expensive than steel or cast iron. Because concrete structures are commonly found in urban environments, this material is often more compatible with the surrounding context. Reinforced concrete barriers can be both poured-in-place and precast. m Stone or granite security elements must be larger than steel or reinforced concrete elements and are often used in enclosed earthen walls or as benches. Granite is very durable and attractive, complementing the architecture of many buildings. 4.3.2 BArrier types There are two basic categories of barriers: passive (fixed) and active (operable).

Passive barriers are fixed in place, do not allow for vehicle entry, and are used to provide perimeter protection away from vehicle access points. Fo\ r jurisdictional purposes, they may typically be categorized into four typ\ es:

m Devices placed within the property lines of a building; they are usually\ not subject to city rules or regulations. m Devices that are installed in the public right-of-way and that are under\ the jurisdiction of local planning and transportation regulations. m Devices installed in privately maintained and privately owned public spaces (such as plazas built on private property in exchange for floo\ r area bonuses) are usually under the jurisdiction of the local planning department. Perimeter security design 4-14 m Devices installed on federal and state land are not required to comply with local regulations, although typically federal and state agencies work cooperatively with local departments. Passive barriers include:

m Walls, berms, and ha-ha barriers m Engineered planters m Fixed bollards, heavy objects, reinforced street furniture, fixtures, \ and trees m Water obstacles m Jersey barriers in fixed and anchored installations m Fences These are listed in approximate order of typical impact ratings, with th\ e highest first. Examples of crash ratings for engineered barriers are g\ iven in the type descriptions below.

Active barriers are used at vehicular access control points within a per\ im - eter barrier system, or at the entry to specific buildings within a site, such as a parking structure or a parking garage within an occupied building, to provide a barrier for vehicle screening or inspection; they can be op\ - erated to allow vehicle passage. Catalog items can be obtained with DOS system ratings to resist various levels of impacts. The descriptive term\ i - nology varies among manufacturers.

m Rotating wedge systems m Rising-wedge barricades m Retractable bollards m Crash beams m Crash gates m Surface-mounted wedges and plates These are listed in approximate order of typical impact ratings, with th\ e highest first. Examples of crash ratings for each type of barrier are \ given in the type descriptions below.

Active barriers are mechanical devices produced by a number of special - ized manufacturers. Examples of each type are illustrated below to show designers their typical characteristics. Active devices must be used in \ con - junction with signage, light signals, gatehouses and security personnel:\ Perimeter security design 4-15 these provide a challenging task to design an integrated grouping of ob - jects that are in tune with the building and site.

In addition, some innovative barrier systems have been developed in re - sponse to design and cost-related demands. These include both active and passive devices:

m The NOGO system m The Tiger Trap m The Turntable 4.4 pAssiVe BArriers 4.4.1 WALLs, excAVA tiOns, Berms, ditches, And hA-hA’s Description, Purpose, and Performance t he hardened (or engineered) wall group includes retaining walls and freestanding walls. These may be constructed of reinforced or mass concrete, concrete masonry, brick, and natural stone, or other materials typically reinforced with steel. Walls may be designed to include sections of perforated walls or discontinuous walls to achieve improved appearance while still satisfying security requirements.

Figure 4-9 shows a reinforced concrete barrier wall that incorporates ar\ t work on its face, and Figure 4-10 shows a barrier wall integral with the building face in an urban site. Figure 4-9: r einforced wall barrier with artwork. sOurce: PHOeniX, AriZOnA, POLice dePArtment , tOdd WHite Perimeter security design 4-16 Walls can be engineered to provide any desired level of performance.

It should be noted that concrete can become fragmented by an explo - sion and turn into projectiles that may cause serious damage to life and property.

Berms, excavations, and ditches can be effectively used to stop vehicles from penetrating the restricted territory. Triangular ditches and hillside cuts are easy to construct and can be effective against a wide range of \ ve - hicle types. Side hill cuts are variations of the triangular ditch, adapted to side hill locations, and have the same advantages and limitations. Wi\ th this type of construction, a vehicle will be trapped when the front end falls into the ditch and the undercarriage is hung up on the leading edg\ e of the ditch. Although untested, soil and rock can absorb large amounts of kinetic energy. Typical configurations and dimensions are shown in Figure 4-11. Both the configurations and dimensions should be carefull\ y studied in relation to the types of vehicles expected to be encountered and the desired level of protection.

Figure 4-10: reinforced concrete barrier wall with artwork at the scottish Parliament, edinburgh.

sOurce: enric, mireLLes, BenedA ttA, t AgLiABue (emBt) And rmJm, JOint -Venture ArcHitects, PHOtO: ducciO mALAgAmBA Perimeter security design 4-17 The ha-ha is a form of barrier that originated for aesthetic purposes in\ 17th century England. The barrier was used to prevent cattle from wan - dering up to a country mansion, while at the same time the barrier wall was invisible to the house. This strategy has been adapted for use as a \ se - curity barrier, most notably around the new setting for the Washington Monument. Here it replaces an unsightly circle of Jersey barriers and allows an unimpeded view of its surroundings from the base of the mon - ument. Viewed from outside the site from below, the Jersey barriers are replaced by an elegantly detailed masonry wall. A happy historical refer - ence is that Washington’s home at Mount Vernon used ha-ha’s for their original purpose (Figure 4-12) Figure 4-11: excavations, berms, and ditches.

sOurce: AFter dOd HAndBOOK: seLectiOn And APPLicAtiOn OF VeHicLe BArriers, miL-HdBK-1013/14, 1999 Perimeter security design 4-18 Installation Although mass may provide an effective barrier in such walls as heavy masonry installed in a ha-ha, typical concrete walls require heavy rein - forcing. Figure 4-13 shows a typical engineering detail of a low anti-ra\ m wall and indicates the necessary dimensions and reinforcing for effective performance.

Design Implications Unless carefully placed and designed, barrier walls can be intrusive elements. They should, as far as possible, only be used where a wall is \ es - sential, and where efforts are made by design and materials to reduce th\ e negative impact. Ha-ha’s are an effective way of providing a non-intrusive barrier that can be integrated into the landscape. Figure 4-12:

Top: Ha-ha diagram (sOurce: ncPc).

Center left: Jersey barriers at the Washington monument.

Center right and bottom: Ha-ha’s at the Washington monument. Perimeter security design 4-19 4.4.2 engineered pLAnters Description, Purpose, and Performance Well-designed planters can form an effective vehicle barrier. Planters located on the surface rely on friction to stop or delay a vehicle, and will be pushed aside by any heavy or fast-moving vehicle; displaced planters may become dangerous projectiles. Engineered planters need considerable reinforcing and below-grade depth to be effective and become fixed elements in the landscape design. The planter shown provides DOS K12 performance (Figure 4-14).

Protection may also be enhanced by the use of crash-rated bollards con - cealed in planters (Figure 4-15). Figure 4-13: engineering detail of anti-ram low wall, to illustrate concept only; dimensions and reinforcing will vary.

sOurce: dOs Perimeter security design 4-20 Installation Some security guidelines for planter system installation are:

m Rectangular planters should be no more than two feet wide, and circular planters should be no more than three feet wide. The horizontal dimension of rectangular planters should not exceed six feet. These, however, are not the best sizes for viable plantings. Figure 4-14: typical engineering detail of reinforced planter with dO s K12 performance, to illustrate concept only; dimensions and reinforcing will vary.

sOurce: dOs Figure 4-15: Planter with concealed crash-rated bollards.

sOurce: WAusAu tiLe Perimeter security design 4-21 m A maximum distance of four feet, depending on the kind of traffic anticipated, should be maintained between planters and other permanent streetscape elements including, but not limited to, fire hydrants, light poles, mailboxes, trees etc. Any greater distance will allow a small car with a few hundred pounds of explosives to pass through. m Planters should be oriented in a direction parallel to the curb or primary flow of pedestrian traffic. In no case should a planter or line of planters be placed perpendicular to the curb. m Landscaping within planters should be kept below two-and-a-half feet, except when special use requirements call for increased foliage (Figure 4-16). In addition, planters should not have enough vegetation to hide a package six inches thick, a briefcase, or a knapsack. m Planters should contain live landscaping at all times and be regularly cleaned of trash and debris. m Planters should not be used in high pedestrian traffic areas. In these locations, bollards or other less obtrusive objects are appropriate. m Planter design, location, and maintenance should create viable conditions for healthy plants. These include adequate water or irrigation, appropriate soil mixture, and selection of plants appropriate to be grown in planters. Seasonal characteristics and ultimate size of plant material shape the choices. Figure 4-16: Large planters as a barrier. the small planters de-emphasize the scale for the open- air restaurant. despite the large planters, the effective sidewalk width remains wide. Perimeter security design 4-22 Design Implications Planters can have a heavy impact on pedestrian movement, reducing the effective sidewalk width — the portion of the sidewalk that can be ef\ fec - tively used by pedestrians, defined as the width of the sidewalk minus\ the width of obstructions and the distance people stay away from them.

However, well-designed and placed planters can have multiple functions and be civic amenities.

4.4.3 fixed BOLLArds Description, Purpose, and Performance A bollard is a vehicle barrier consisting of a cylinder, usually made of steel and filled with concrete placed on end in a deep concrete footing in the ground to prevent vehicles from passing, but allowing the entrance of pe\ - destrians and bicycles. Bollards are also constructed of steel sections and reinforced concrete. An anti-ram bollard system must be designed to ef - fectively arrest the vehicle and its cargo as quickly as possible and no\ t create an opening for a second vehicle.

A typical fixed anti-ram bollard consists of a ½-inch thick steel p\ ipe, eight inches in diameter projecting about 30 inches above grade and buried about 48 inches in a continuous strip foundation (Figure 4-17).

The bollard shown in Figure 4-17 would be capable of stopping a 4,500-lb\ .

vehicle traveling at 30 mph. Rated bollards are also available that woul\ d provide protection up to DOS K12 level. Figure 4-17: d iagram of typical bollard installation. t o illustrate concept only: dimensions and reinforcing will vary. sOurce: dOs Perimeter security design 4-23 Bollards can be specified with ornamental steel trim attached directly to the bollard or with selected cast sleeves of aluminum, iron, or bronze t\ hat slip over the crash tube. Bollards can be galvanized against corrosion and fitted with internal illumination for increased visibility. Figure 4-18 shows a number of decorative bollards with high-performance ratings. Bollards may be custom designed for an individual project to harmonize with the materials and form of the building, but to ensure adequate protection, they would need to be tested by an independent laboratory (Figure 4-19).

. Figure 4-18: decorative bollards with high-performance ratings. sOurces: tOP LeFt And rigHt: secureusA, inc.

BOttOm LeFt: deL tA scientiFic cOrP.

Figure 4-19: c ustom-designed steel bollards that match the design of their buildings Perimeter security design 4-24 Commonly used decorative bollards without deep foundations do not have anti-ram capacity, though they may provide some deterrence value by making the building look more protected than it is.

Installation The need for bollards to penetrate several feet into the ground may caus\ e problems with below-ground utilities whose location may not be known with certainty (Figure 4-20). If underground utilities make the installation of conventional bollard foundations too difficult, a possible solution is to use bollards with a wide shallow base and a system of beams below the pavement to provide resis - tance against overturning (Figure 4-21). Figure 4-20: i nstallation of fixed bollard line. note the depth and size of the excavation. sOurce: secureusA, inc.

Figure 4-21: example of bollards with a wide shallow base and a system of beams. sOurce: rsA PrOtectiVe tecHnOLOgies Perimeter security design 4-25 Design Implications Bollards are by their nature an intrusion into the streetscape. A bollard system must be very thoughtfully designed, limited in extent and well in - tegrated into the perimeter security design and the streetscape in order to minimize its visual impact The visual impact of bollards can be reduced by limiting height to no more than 2 feet 6 inches. However, the height of the curb and its po - sition relative to the bollard also relates to the bollard height. This and other site specific conditions such as road surface grade, may help to maintain an effective bollard for impact while making the bollard appear visually less obtrusive. In addition, the design basis threat, in terms \ of ve - hicle size and speed, also influences bollard height. In no case should bollards exceed a height of 38 inches inclusive of any decorative sleeve\ .

A bollard reduces the effective sidewalk width in a pedestrian zone by the width of the curb to bollard (typically 24 inches, plus the width of th\ e bol - lard). In several high-pedestrian and narrow-sidewalk areas of a central business district, the reduction in effective sidewalk width can prove c\ ritical.

Other bollard system guidelines are:

m Spacing between 36 and 48 inches depending on the kind of traffic expected and the needs of pedestrians, people with strollers and wheel chairs and the elderly must be considered. m In long barrier systems, the bollards should be interspersed with other streetscape elements such as hardened benches, light poles, or decorative planters. m They should be kept clear of ADA access ramps and the corner quadrants at streets. m They should be arranged in a linear fashion in which the center of the bollards is parallel to the center line of existing streets. 4.4.4 heAVy OBjects And trees Description, Purpose, and Performance Heavy objects, such as large sculptural objects, massive boulders, eart\ hen berms or concrete forms with unassailable slopes, and dense planting and trees can be used in a similar way to bollards to prevent vehicles from passing, while allowing the passage of pedestrians and bicycles. To ensure that such barriers can effectively reduce the threat level, engineering \ de - sign and/or evaluation is necessary. For example existing dense thickets of mature trees can be incorporated into a perimeter system (Figure 4-22)\ . Perimeter security design 4-26 Specially designed objects that also serve a practical and aesthetic purpose can be used as effective barriers (Figures 4-23, 4-24, 4-25, and 4-26)\ . Figure 4-23: c ombination low retaining wall and sculptural object as a barrier system. Figure 4-22: g roups of mature palm trees as protection from vehicular intrusion.

sOurce: PHOeniX POLice dePArtment , AriZOnA center, rOuse deVeLOPment cO. Perimeter security design 4-27 Figure 4-24: decorative obelisk at the approach to a civic Plaza.

sOurce: PHOeniX, AriZOnA, POLice dePt ., tOdd WHite. Figure 4-25: group of engineered sculptured objects as a barrier.

sOurce: PHOeniX, AriZOnA, POLice dePt., tOdd WHite. Perimeter security design 4-28 Figure 4-27 shows the use of custom bollards in combination with large rocks. The rocks have symbolic meaning as part of the landscaping of the space but are also engineered barriers. Figure 4-26: An array of rocks form an effective barrier.

Figure 4-27: selected rocks and custom bollards as barriers: scale and placement provide nonintrusive security. Perimeter security design 4-29 Installation Objects used as barriers will need varying degrees of embedment and rein - forcement, depending on their weight, footprint, and height/width ratio.\ Design Implications The use of natural features such as rocks, or man-made objects such as sculpture, provides opportunities for creating barriers that can enhance the visual environment, effectively delineate pathways, clarify public and private space, and provide protection in an unobtrusive manner.

4.4.5 WAter OBst AcLes Description, Purpose, and Performance One of the oldest forms of site security design is that of water. Used in the form of artificial or natural lakes, ponds, rivers, and fountains, wat\ er can be an effective and beautiful choice for a barrier. The configuration of the channel can be designed as an effective "tank trap," or walls of the pool or mass of the fountain can be engineered to stop a vehicle. The water can be presented in a variety of ways — flat and smooth or enhanced\ with movement by falls or fountains. Water features generally require ongoing maintenance with filters, pumps, cleaning, etc. (Figure 4-28). Figure 4-28: this proposal for the re-design of the Washington m onument grounds uses water to create a barrier. the meandering canal is quite beautiful as well as functional. sOurce: micHAeL VAn VAndenBurgH And AssOciA tes Perimeter security design 4-30 An example of a water barrier in an urban setting is also shown in Chapt\ er 6, Section 6.4, Figure 6-19.

4.4.6 jersey BArriers Description, Purpose, and Performance A Jersey barrier is a standardized precast concrete element originally d\ e - veloped in the 1940s and 1950s by New Jersey, California, and other states as a median barrier to prevent vehicle crossovers into oncoming traffi\ c.

The New Jersey barrier became the most widely used and gave its name to the generic barrier type. Subsequently, the barrier was widely used for temporary protection in highway and other construction projects, and came into wide use after September 11, 2001, as an anti-ram and traffi\ c control barrier against terrorist attack.

The barriers are not easily adaptable: they come in standard lengths of 12.5 and 20 feet, making their use somewhat inflexible, and they must be carefully installed or they may create undesirable spaces where they overlap, and reduce sidewalks to non-navigable widths (Figure 4-29).

Jersey barriers were thought to provide protection through their mass — a 12-foot barrier weighs approximately 5,700 pounds — but if pla\ ced on the surface, they are ineffective against vehicular attack. To be effec - tive, they need embedment and vertical anchorage by steel reinforcing through the foundation.

The Jersey barrier shown in Figure 4-30 is capable of stopping a 4,000-l\ b.

vehicle traveling at 50 mph and a 12,000-lb. vehicle traveling at 25 mph\ .

Note that the barrier is embedded about 12 inches and anchored to the concrete slab with reinforcing bars: in this installation, the barriers essen - tially become permanent (Figure 4-30). Figure 4-29: Jersey barriers: pedestrian disruption at the White House (left) and o\ n a d.c. street (right). Perimeter security design 4-31 Installation When installed on a sidewalk, a Jersey barrier reduces the effective sid\ e - walk width by three-and-a-half feet, plus whatever distance it is placed\ from the curb. Some installations can be dangerous in the event of an emer - gency evacuation, particularly when several barriers are connected witho\ ut breaks, because there is no easy way for pedestrians to move past them.

Design Implications Relatively inexpensive and readily available, Jersey barriers became ubi\ qui - tous in the protection of public buildings and monuments in Washington, New York, and elsewhere. However, their often awkward placement may degrade the beauty of the urban scene and disrupt access and movement for those on affected streets and sidewalks. Their most effective use is\ on a temporary basis.

4.4.7 fences Description, Purpose, and Performance Fences are a traditional choice for security barriers, primarily intende\ d to discourage or delay intruders or serve as a barrier against stand-off weapons (e.g., rocket-propelled grenades) or hand-thrown weapons such as grenades or fire-bombs. Familiar fence types include:

m Chain-link m Monumental fences (metal) Figure 4-30: Jersey barrier dimensions and installation for high level of protection.

sOurce: dOd HAndBOOK: SELECTION AND APPLICATION OF VEHICLE BARRIERS , miL- HdBK-1013/14, 1999 Perimeter security design 4-32 m Anti-climb (CPTED) fence m Wire (barbed, barbed tape or concertina, triple-standard concertina, tangle-foot) Descriptions of these fence types can be found in FEMA 426, Section 2.4.\ 1.

These fencing types are primarily intended to delay intrusion; they pro - vide limited protection against vehicles unless specially designed to b\ e crash-rated.

Fencing can also incorporate various types of sensing devices that will relay warning of an intruder to security personnel. Concealed intrusion detection systems are also available, incorporating buried field units\ and sensor cables.

Fences can also be constructed as engineered anti-ram systems. A typical solution is to use cable restraints to stop the vehicle: these can be placed at bumper height within the fence, hidden in planting. The cable needs to be held in place using bollards and anchored to the ground at the ends (Figure 4-31).

High-security cable fencing is available that can provide protection to the original DOS Standards of providing an L1 rating (20 to 50 feet penetra\ - tion) or L2 rating (3 to 20 feet penetration). Figure 4-31: Layout of cable barrier, used in conjunction with fence or planting. sOurce: dOd HAndBOOK: seLectiOn And APPLicA tiOn OF VeHicLe BArriers, miL- HdBK-1013/14, 1999 Perimeter security design 4-33 Installation Cable system fences allow considerable deflection before vehicles are stopped; vehicles will be able to partially penetrate the site before re\ - sistance occurs. The amount of deflection is based upon the distance between the concrete “deadmen” — typically about 200 feet. As a\ re - sult, the siting requirements for fences and gates that incorporate a cable system differ slightly from other types of walls and fences. The designe\ r should take this into consideration when these types of systems are bein\ g considered. Conventional fences with crash ratings can also be provided (Figure 4-32).

Design Implications Fences for the protection of property have a long history and have also often been elements of great beauty. Modern fences are governed more by function and cost, but variations of historic fence design have been used as barriers for important historic buildings. The appearance of les\ s attractive fencing can be improved by planting.

4.4.8 reinf Orced street furniture And fixtures Description, Purpose, and Performance Common streetscape elements can be reinforced to serve as anti-ram barriers. These elements can be designed to be “hardened” so that \ they function both as amenities and as components of physical building perim - eter security. The structural design, spacing, shape and detailing of the perimeter security components must be designed to address the required Figure 4-32: crash-rated fence. sOurce: Amerist Ar Fence PrOducts inc. Perimeter security design 4-34 level of protection for a particular building. Typical elements that lend themselves to this approach include hardened street furniture, fences or fence walls, plinth walls (low retaining walls), bollards, planters, l\ ight stan - dards, bus shelters etc (Figure 4-33). Figure 4-33: streetscape elements suitable for hardening as security elements sOurce: ncPc Perimeter security design 4-35 To date, bollards have tended to become ubiquitous as perimeter barrier systems. Security device manufacturers have found sufficient demand to\ justify development and testing of active and passive bollards. They hav\ e also responded to design demands by providing decorative covers in a number of materials, which has greatly improved their appearance, but there is need for more variety in barrier system design. This variety ca\ n be provided by the use of hardened streetscape elements, but this ap - proach has been limited due to the lack of tested and certified exampl\ es.

Development of such elements is important to enable the design of an at - tractive and secure urban environment. An improvised example of this approach, using crash rated bollards concealed between two benches, is shown below ((Figure 4-34).

Supplementing bollards with common other reinforced streetscape compo - nents such as lamp standards, bus shelters, and kiosks can assist in rel\ ating security design to the community context. Such components would need testing to ensure acceptable performance, but the use of custom-designed components would enhance the streetscape and add an additional level of safety to pedestrians against everyday traffic accidents. Some example of these applications are shown in the following graphic boxes. Figure 4-34: Outdoor seating reinforced with hidden bollards. sOurce: secure usA, inc. CUSTOM STREET FURNITURE BARRIERS Perimeter security design 4-36 CUSTOM STREET FURNITURE BARRIERS (continued) Perimeter security design 4-37 An example of a custom-designed streetscape feature is that of reinforce\ d glass seating that provides a considerable level of protection, looks at\ - tractive, and can be illuminated to provide additional night protection \ at locations such as bus stops (Figure 4-35). Figure 4-35: reinforced and illuminated glass bench model. sOurce: rOgers mAr VeL ArcHitects, LLc CUSTOM STREET FURNITURE BARRIERS (continued) Perimeter security design 4-38 4.5 ActiVe BArriers 4.5.1 retrAct ABLe BOLLArds Description, Purpose, and Performance A retractable bollard system consists of one or more rising bollards operating independently or in groups of two or more units. The bollard is a below-ground assembly consisting of a foundation structure and a heavy cylindrical bollard that can be raised or lowered by a buried hydraulic or pneumatic power unit, controlled remotely by a range of access control devices. Manually operated systems are also available: these are counter-balanced and lock in the up or down posi - tion. Typical retractable bollards are 12 to 13 inches in diameter, up to 35 inches high, and are usually mounted about three feet apart, depending on the type of traffic. Figure 4-36 shows typical installations of retractable bollards, with fixed bollards to each side of the retractable array. Figure 4-36: typical retractable bollard systems at a service entry (left) and a parking garage (right). note the fixed bollards to each side of the retractable arrays. Retractable bollards are used in high-traffic entry and exit lanes where vehicle screening is necessary, at site entrances, and at entries to parking garages and building services. Unlike rising or rotating wedge barriers, the entry is freely accessible to pedestrians when the bollards are raised.

Normal bollard operating speed is field adjustable and ranges from 3.0\ to 10.0 seconds. Emergency operating systems can raise bollards to the guard position from fully down in 1.5 seconds.

Retractable bollards are available crash rated up to DOS K12 standard. Perimeter security design 4-39 Installation Retractable bollards are expensive because they need deep and broad ex - cavation for the bollards and operating equipment. Figure 4-37 shows a single bollard installation and the installation requirements for a set \ of bollards. Figure 4-37: retractable bollard installation section (top) and installation requirements for power and control of a set of bollards (bottom).

sOurce: deLtA scientiFic cOrP. Perimeter security design 4-40 m Retractable bollards are a relatively unobtrusive barrier, which need only be raised when screening is necessary, although at a time of heightened threat they can remain in their raised position. A variety of\ ornamental sleeves can be provided. Retractable bollards are generally accompanied by fixed bollards at the sides, and a secure control booth\ is necessary for security personnel. 4.5.2 rising Wedge BArriers Description, Purpose, and Performance Wedge barriers, sometimes called rotating plate barriers, consist of a metal plate installed in a roadway that can be raised or lowered by an attenda\ nt usually located in a booth next to the metal plate, thus regulating vehicle access to the street across which it is installed. These barriers can be\ crash rated and can effectively stop vehicles. Their primary purpose is to create a restricted area by regulating vehicle access, rather than to block an \ area from all vehicles. Shallow foundation systems are available rated to DOS\ K12 standard. Raised height is from about 21 inches to 38 inches, and a standard width is 10 feet. In the retracted position, the heavy steel ra\ mp will support any permitted road transport vehicle axle loadings. The moving plate is raised and lowered by a hydraulic or pneumatic system (Figure \ 4-38). Figure 4-38: rising wedge barriers.

sOurce: deLtA scientiFic cOrP. Perimeter security design 4-41 Installation Wedge barriers can be surface mounted, or mounted in a shallow excava - tion about 18 inches deep. In the latter installation, the barricade plate is flush with the road surface when retracted. The power unit can be config - ured to operate one or more barricades and can be operated by a range of optional remote control inputs. In surface-mounted installations, all components are mounted above grade; no cutting or excavation is re - quired on good concrete surfaces.

Mobile wedge barriers are also available that can be moved into position\ by a medium-sized pickup truck in 15 minutes. These can form an effec - tive element of a planned temporary barrier to respond to a heightened threat level (Figure 4-39).

Design Implications Rising wedge barriers were one of the earliest active barrier systems to be developed. They are somewhat utilitarian in appearance, compared to re - tractable bollards or rotating wedge systems.

These barriers effectively restrict vehicular through movement, but care must be taken to ensure that limitations on the passage of screened bic\ y - cles, cars and emergency vehicles are minimized. Like all active barrier\ s, mobile wedge barriers must be attended at all times. Figure 4-39: mobile wedge barrier. sOurce: deL tA scientiFic cOrP. Perimeter security design 4-42 4.5.3 rOtAting Wedge systems Description, Purpose, and Performance These systems are similar in action to the rising wedge blocker outlined in Section 4.5.2 but have a curved front face, providing a better appear - ance, and are embedded to a grater depth. The height of the obstacle is between 24 and 28 inches, and a standard width is 10 feet. The obstacle is operated hydraulically by heavy duty rams. Operating time is about three seconds per movement (Figure 4-40). Figure 4-40: typical rotating wedge barrier dimensions and installation requirements. sOurce: deL tA scientiFic cOrP. Installation The pit to receive the system is approximately 5 feet wide, 40 inches de\ ep, and about 6 inches wider than the width of the obstacle. The hydraulic mechanism can be located up to 50 feet away from the barrier.

Design Implications Appearance depends on the layout and design of any accompanying fixed barriers and control booths, the design of operating buttresses, and the color and pattern of the barrier (Figure 4-41). Perimeter security design 4-43 4.5.4 drOp Arm crAsh BeAms Description, Purpose, and Performance Drop-arm crash beams are a greatly strengthened version of barriers fa - miliar at parking garage entries and the like. To create a crash barrier, the assembly consists of a steel crash beam, support and pivot assembly, cast- in-place concrete buttress, and locking and anchoring mechanisms. In addition, crash-rated beams incorporate a high-strength steel cable, whi\ ch is attached to both buttresses when the arm is in a down position. Clear\ opening range is from about 10 to 24 feet. The arm is raised and lowered using a hydraulic or pneumatic system, or manually with a counter-bal - anced arm (Figure 4-42). Figure 4-42: drop-arm crash beam. Figure 4-41: rotating wedge installation with typical manufacturer’s jazz pattern (left), rotating plate barrier with stop sign in an elegant font combined with well-designed fixed low bollards\ (right). Perimeter security design 4-44 While crash-rated drop beams can be obtained, their performance is typ - ically less effective than other active systems, although barriers can b\ e obtained with a certified K12 performance rating.

4.5.5 crAsh gAtes Description, Purpose, and Performance Crash-rated gates can be obtained that operate without contact with the ground, while others use a rack-and-pinion drive across a V-groove. Swing versions are also available. Clear opening range is from about 12 feet t\ o 30 feet. Typical heights are 7 feet to 9 feet (Figure 4-43). Crash ratings up to DOS K12 can be obtained. Figure 4-43: typical gate installation (left); sliding gate with K12 crash rating (\ right). sOurce: deL tA scientiFic cOrP. 4.5.6 surf Ace-mOunted rOt Ating pLA tes Description, Purpose, and Performance Surface-mounted wedges and plates are modular bolt-down barrier sys - tems in which all components are mounted above grade, and no cutting or excavation is needed on most concrete surfaces. The moving plate or wedge is raised and lowered by a hydraulic, pneumatic or electro-mechan - ical drive. A typical unit incorporates a single buttress with a ramp wi\ dth of 10 feet and a raised height of 21 to 28 inches. Dual buttress systems have a width of about 18 feet. These systems can be installed quickly an\ d removed easily. Some systems incorporate a drop arm and traffic lights for additional safety (Figure 4-44).

Typical cycle time is three to four seconds with a 1.5 second emergency cycle. High-performance systems are capable of a DOS K4 rating. Perimeter security design 4-45 4.6 innOVAtiVe BArrier systems A fter September 11, 2001, designers outside the traditional security industry began to develop systems that combine func - tionality with better appearance and, in some cases, lower cost. The use of the ha-ha, described in Section 4.4.1, is an example of a tra\ di - tional barrier imaginatively adapted to meet a contemporary and quite different need. Three innovative systems are described in Section 4.6.1.\ The NOGO barrier and “TigerTrap” are passive systems, while the “Turn - table” is an active barrier.

4.6.1 the nOgO BArrier Originally designed for the Wall Street area of New York City, the NOGO barrier is an example of a device that provides an effective vehicle bar\ - rier, while also being visually attractive and useful to lean on, socialize \ or enjoy a lunch around, and as such makes a positive contribution to the streetscape. The NOGO barrier is part security device and part a public art object and has been exhibited at the New York Museum of Modern Art. While more expensive than bollards, these simple yet subtle bronze forms of a beautiful material provide a lasting benefit to the street scene (Figure 4-45). Combined with the Turntable (see below) the NOGO, can also be part of an active anti-ram system.

Figure 4-44: surface-mounted wedges: single buttress with lighting (left); dual buttress with drop arm (right).

sOurce: secureusA inc. Perimeter security design 4-46 4.6.2 the tigertrAp The TigerTrap is a collapsible sidewalk and planting system designed to reduce the impact of force protection on public space while maintaining a high level of security. The TigerTrap employs a sub-grade collapsible material, installed below at-grade paving or planting. The installation is designed to withstand pedestrian traffic but fail under the weight \ of a loaded vehicle. The collapsible material lowers the elevation of an at\ - tacking vehicle, so that it may be stopped by a low bench or underground foundation wall. The system employs a compressible concrete technology developed as an aircraft arrestor system that is installed at the end of the overrun section of runways, instead of net systems commonly used.

The system is designed for use in sites where there is considerable spac\ e available. The TigerTrap has been crash tested by the U.S. Army Corps of Engineers and has been demonstrated to be approximately equivalent to the DOS K12 standard.

The system needs careful design to be effective against design threat ve\ - hicles without blocking lighter vehicles such as golf carts and motorize\ d wheel chairs; it needs considerable length to be effective (Figures 4-4\ 6, 4-47). Figure 4-45: nO gO bronze sculptured barriers.

sOurce: rOgers mAr VeL ArcHitects, LLc Perimeter security design 4-47 4.6.3 the turntABLe VehicLe BArrier The Turntable Barrier concept was designed specifically to overcome diffi\ - culties of installation in an urban environment, by use of a state-of-th\ e-art technology in operable anti-ram devices, while fostering a positive pede\ s - trian environment (Figure 4-48). Figure 4-46: the tigertrap concept.

sOurce: rOcK 12 security ArcHitecture Figure 4-47: Planting cover layer creates a t igertrap planting with a rear bench.

sOurce: rOcK 12 security ArcHitecture Perimeter security design 4-48 The Turntable Vehicle Barrier is a shallow-foundation operable de - vice designed to provide the function of retractable bollards without deep foundations. The foundation requires less than 2 ½ feet of depth\ , placing the installation above most underground utilities. The turn - table employs a non-hydraulic friction wheel drive system, a proven technology used in rotating structures all over the world that alleviates many of the operational and maintenance difficulties associated with hydraulic devices. The rotational movement, while rapid enough for se - curity purposes, does not pose a pedestrian danger.

The turntable is presently undergoing an extensive program of crash testing to obtain certification.

The surface of the turntable is designed to accept a paving layer to match surrounding materials, and the impact posts can accept covers of any shape and size, such as architectural metals, walls, or planters (Figure 4-49). Figure 4-48: turntable designed for conditions where security devices do not fit easil\ y amid the tangle of underground utilities and infrastructure.

sOurce: rOcK 12 security ArcHitecture Perimeter security design 4-49 Figure 4-49: shallow depth allows the turntable to avoid underground utilities. impact posts keep the street open to pedestrians (top), and the turntable can accept architectural covers on the impact posts and matching paving to the surrounding roadway (right).

sOurce: rOcK 12 security ArcHitecture 4.7 cOncLusiOn t he design of the perimeter barrier system is one of the most im - portant aspects of providing building security. Design practice has evolved rapidly from the hasty installation of Jersey barriers after September 11, 2001, to the more considered designed systems that repre - sent today’s best practice.

Today’s best practices often involve imaginative use of both traditional and new concepts and materials, in the attempt to balance the needs of security with those of site amenity and everyday function. They have been developed in response to the perceived shortcomings of initial so - lutions. Too often these solutions, conceived to be temporary, lasted for many years, and some have become all but permanent. To the extent that this has happened, and the visual and functional quality of our en - vironment has been de-humanized, it can be said that the terrorists have\ gained a victory. Perimeter security design 4-50 Access and egress control points need careful design and location, be - cause they weaken the security of the perimeter. On the other hand, a second point of egress is necessary in case an egress point is shut down by police action, bomb squad activities, or other incidents.

The examples in this publication show that imaginative design of barrier\ systems can provide positive enhancement of the urban environment, by more clearly defining the types of public and private space and by pro\ - viding city goers with more protection from everyday traffic. Innovation in barrier design is also underway, spurred on by the needs of special situ - ations such as the New York financial district, which is both high risk and historic. The aim should be to develop building protection methods that are unobtrusive elements in a safe and attractive streetscape.