One of the most basic threats facing any facility is from intruders accessing the facility with the intention of causing damage to its assets. These threats may include intruders actually entering the facility, as well as intruders attacking the facility from outside without actually entering it (i.e., detonating a bomb near enough to the facility to cause damage within its boundaries).

One of the most effective ways to counter the threat of intruders accessing a facility or the facility perimeter is to install security barriers around the facility's perimeter. Security barriers are large, heavy structures that are used to control access through a perimeter by either vehicles or personnel. They can be used in many different ways depending on how/where they are located at the facility. For example, security barriers can be used in or along driveways or roads to direct traffic to a checkpoint (i.e., a facility may install jersey barriers in a road to direct traffic in certain direction). Other types of security barriers (crash beams, gates) can be installed at the checkpoint so that guards can regulate which vehicles can access the facility. Finally, other security barriers (i.e., bollards or security planters) can be used along the facility perimeter to establish a protective buffer area between the facility and approaching vehicles. Establishing such a protective buffer can help in mitigating the effects of the type of bomb blast described above, both by potentially absorbing some of the blast, and also by increasing the "stand-off" distance between the blast and the facility (the force of an explosion is reduced as the shock wave travels further from the source, and thus the further the explosion is from the target, the less effective it will be in damaging the target).

Security barriers can be either "active" or "passive." "Active" barriers, which include gates, retractable bollards, wedge barriers, and crash beams, are readily movable, and thus they are typically used in areas where they must be moved often to allow vehicles to pass - such as in roadways at entrances and exits to a facility. Active security barriers will be discussed in the Active Security Barriers document. In contrast to active security barriers, "passive" security barriers, which include jersey barriers, bollards, and security planters, are not designed to be moved on a regular basis, and thus they are typically used in areas where access is not required or allowed - such as along building perimeters or in traffic control areas. Passive security barriers are typically large, heavy structures that are usually several feet high, and they are designed so that even heavy-duty vehicles cannot go over or through them. Therefore, they can be placed in a roadway parallel to the flow of traffic so that they direct traffic in a certain direction (such as to a guardhouse, a gate, or some other sort of checkpoint), or perpendicular to traffic such that they prevent a vehicle from using a road or approaching a building or area. This document will focus exclusively on passive security barriers.

Descriptions of the different types of passive security barriers are provided below:

"Jersey barrier" is a generic term for a long barrier that is broad at the bottom and tapers towards the top. These types of barriers are often used as medians in roads, especially during construction or when flexibility is needed to change traffic patterns (these barriers can be moved from one lane to another relatively easily, allowing traffic patterns to be changed as needed). Jersey barriers can be constructed from solid concrete, steel-reinforced concrete, or plastic. Concrete-based barriers are durable and do not deteriorate over time when exposed to ultraviolet light or harsh environments. However, concrete barriers are extremely heavy, and thus they cannot be installed or moved by hand. They are usually installed using a truck-mounted crane or forklift. Plastic jersey barriers consist of lightweight polyethylene shells that can be shipped to where they are needed and then filled with sand, water, or other materials to give them extra weight and stability. In contrast to concrete jersey barriers, these barriers are lighter and easier to transport. They can be stacked and stored, and one person can easily move an empty barrier into its desired position.

Individual jersey barriers can be used as stand-alone barriers, or they can be lined up end-to-end to provide a longer continuous barrier. Various different jersey barriers feature different connecting hardware, including eye hooks and slotted connectors. Because jersey barriers can be used alone or in various groupings, they are ideal for various applications. They can also be moved depending on the area's security needs at any given time. As described above, jersey barriers are often placed parallel to traffic so that traffic is directed in a specific direction. This can ensure that all traffic is directed towards a point where it can be checked, such as towards a gate or guard post. However, jersey barriers can also be oriented perpendicular to potential traffic so that no traffic can access an area. An example of this type of application would be jersey barriers set up around a building, so that no vehicles can get close to that building. Keeping vehicles at a safe distance from a building helps to ensure not only that vehicles cannot ram the building, but that explosive devices (i.e., car bombs) or other dangerous materials are not brought into close proximity to a building.

There are two major jersey barrier designs. The older "C"-type barriers are tapered towards the top; however, the newer "F"-type barriers have been designed to flare out somewhat near the top. This provides extra weight to the barrier and also makes it more difficult to drive over the top of the barrier. Table 1 summarizes the advantages and disadvantages of jersey barriers.

Bollards are cylindrical barriers that are placed at discrete intervals in a traffic area such that they block vehicles from passing between them, while allowing pedestrians through. The concept behind a bollard barrier system is to obstruct part of the pathway of a vehicle. The bollards are typically placed 4-5 feet apart so that vehicles cannot pass between them without hitting the bollards. Bollards are typically at least 3 feet high (some may be 7 feet tall or higher) so that vehicles cannot go over them without becoming stuck or damaging their transmissions. Typical bollards are 1-2 feet in diameter, and many are specifically designed to withstand vehicular impacts without crumbling or breaking off. Thus, even if a vehicle hits a bollard directly, it cannot pass over or through it.

Bollards can be constructed from many different types of solid materials, including concrete, steel-reinforced concrete, cast iron, stainless steel, or galvanized steel. The choice of material for any given bollard will depend on its intended application. For example, removable and retractable bollards are typically constructed from stainless or galvanized steel, whereas concrete and cast iron is typically used only for fixed bollards. Each also has advantages and disadvantages relative to the potential threat for that facility. For example, concrete bollards are inexpensive compared to bollards constructed from other materials, and these types of bollards may be ideal for harsh environments because they do not rust or deteriorate, and they do not require painting. However, concrete is brittle, and thus it may not have a high impact resistance. Designing the concrete with an internal reinforcing rebar core can add impact resistance to a concrete bollard.

In contrast to concrete bollards, steel bollards have a higher strength and thus more intrinsic crash resistance. However, they are more expensive than concrete bollards, and they must be maintained so they do not rust.

Bollards can be fixed in place, removable, or retractable. Fixed and retractable bollards will be discussed in this document; retractable bollards will be covered in the Active Security Barriers Product Guide.

Fixed bollards can be constructed from any type of material. They are anchored in place as needed, and are typically used along sidewalks or in areas where traffic can be blocked permanently. These types of bollards are anchored by imbedding them into the ground/driveway surface using some type of anchoring material (typically concrete, although some bollards may be imbedded using only native soil if the soil is very compact). Some bollards have side pins that extend out from the bollard's base into the imbedding matrix. These pins can provide extra impact stability to the bollard. Specific vendors can be consulted to determine the relative value (in terms of crash stability) of using pins vs. imbedding the base of the bollard deeper into the soil; however, pins may be necessary in areas where the bollards cannot be buried deeply. Fixed bollards are shipped with any necessary installation equipment (i.e., pins) and are installed as needed at the facility. Installing a fixed bollard is similar to installing a fence post. Table 2 summarizes the advantages and disadvantages of fixed bollards.

Removable bollards can be screwed into casements anchored within the roadway or sidewalks, and can be removed as necessary when vehicular access to the protected area is needed. However, installing and removing these types of bollards can be labor intensive and time consuming; there are also concerns that these types of bollards may not be as strong at the base as fixed bollards. Therefore, these types of bollards are usually used when roads or sidewalks are to be blocked off for some length of time, but not permanently. Removable bollards are typically constructed from steel or other materials that have a low weight-to-volume ratio to make them easier to remove. Concrete is not usually used for removable bollards. Table 3 summarizes the advantages and disadvantages of removable bollards.

Security planters are large, bowl-shaped structures that are planted with flowers, trees, or other plants. They are typically located near the entrances to buildings or on sidewalks in front of buildings, where they provide both physical bulk to prevent vehicles from driving onto the sidewalk, and aesthetic enhancements to the area. Like bollards, they are typically spaced a few feet apart to block a vehicle's path towards the building. Planters are typically constructed of concrete to provide some vehicle stopping power, and the dirt and/or plants within the planter may provide extra drag on a vehicle attempting to drive through a planter. Dimensions of security planters vary by vendor, and they are often custom-designed to the end-user's needs. Typical use of these types of barriers would be in lower-security applications where less crash resistance or protection is needed than would be provided by bollards or jersey barriers; or in applications where aesthetic concerns and the need to camouflage the security barrier are major concerns. Table 4 summarizes the advantages and disadvantages of security planters.

The primary attributes of passive security barriers are their size, strength, and impact resistance. These features are discussed in more detail below.

One of the major design principles behind passive security barriers is their size. They are designed so that they will impede the path of vehicles, and so they must be of sufficient size (both in bulk and in height) so that vehicles cannot drive over or around them. Most security barriers are at least 3 feet high, which places them at least at the grill level of most vehicles. Because they are at the grill level, these barriers will penetrate through to the engine block, or become lodged underneath the vehicle and destroy its transmission, if vehicles attempt to drive through/over them. This ensures that, even if the vehicle manages to pass the barrier, it will no longer be drivable, and the vehicle will only travel as far past the barrier as its momentum will take it.

The thickness or other lateral dimensions of the barrier may be important in contributing to the overall strength of the barrier (barrier strength is discussed separately below) and in physically blocking more of a partially-obstructed path. This is particularly important for bollards and planters (see further discussion below).

Different security barriers are also sized differently depending on their intended application. For example, jersey barriers are designed to be laid end-to-end to provide a continuous barrier to vehicles, and to direct vehicles to specific access points. As discussed above, these barriers are designed at specific heights to make it more difficult for vehicles to go over them, but because they are typically laid end to end, the individual length of any barrier may not be an important security consideration in choosing individual barriers. Rather, the determining factors in choosing barriers of different lengths may be cost, weight, length of perimeter to be secured, etc.

In contrast to jersey barriers, bollards and planters are not designed to provide a continuous barrier. Rather, they are designed to restrict the amount of open space that can be traversed by a vehicle. However, by placing them at specific distances from each other, they can restrict vehicle access between them. The different diameters of different types of bollards and planters will affect the number of individual barriers that must be used to protect a given perimeter.

In addition to a large size that prevents vehicles from driving over or around security barriers, these barriers must also be strong so that vehicles cannot crash through them. The exteriors of these barriers are typically designed from concrete or steel, which provides some physical resistance to breaking. However, some jersey barriers are constructed from plastic filled with sand or water to give them added bulk. These types of barriers may not be physically strong (they will most likely crack when impacted by a vehicle), but they may provide some resistance or drag to a vehicle hitting them.

However, the primary design factor for the impact resistance of these barriers is their interior core, which is usually constructed from reinforced steel rebar. This is discussed in more detail below.

The ability of the barrier core to successfully withstand an impact is referred to as its impact resistance or crash test rating. Crash test rating specifications are usually given in terms of the barrier's ability to withstand an impact from a vehicle of a certain weight traveling at a certain speed. For example, a barrier may be designed to stop a 15,000-lb vehicle traveling at 50 miles per hour. The primary federal standard for crash rating is the Department of State Specification SD-SDT-0201 (Specification for Vehicle Crash Test of Perimeter Barriers and Gates, April, 1985, updated March 2003). ASTM standard WK2534 is equivalent to this rating. This standard is based on the distance past a barrier that can be penetrated by a 15,000-LB vehicle traveling at different speeds. The vehicle speed is designated as "K," and the distance of penetration past the barrier is designated as "L." These designations are summarized in the Tables 5 and 6 below. Thus, a barrier with a SD-SDT-0201 crash rating of K12/L3 could keep a 15,000 vehicle traveling at 50 mph from penetrating more than 3 feet past the barrier.

For bollards, crash resistance is dependent on the type of bollard, its shape and dimensions, and the depth to which it is anchored into the roadway. Crash resistant bollards are typically constructed from steel. Steel is preferred for crash resistant applications because it can transfer the crash impact throughout the entire bollard, thereby lessening the force at any one point on the bollard and reducing the potential for the bollard to shatter. In contrast, concrete is brittle and can shatter on impact. However, concrete bollards can be reinforced with iron or steel rebar core to add crash resistance. Therefore, many concrete bollards are built around an impact-dampening iron rebar core that can spread the force of the impact over there entire structure and hold the concrete together even after direct impact. In these types of bollards, rebar extends upwards towards the top of the barrier and is anchored approximately 3-4 feet below the roadway.

Manufacturers have developed different barrier systems designed to meet the specifications described in the tables above, and thus individual users can purchase systems that meet the most likely threat scenarios they have identified for their facilities.

The following table shows cost ranges for each barrier type, along with advantages/disadvantages of each. With most of these security barriers, the major factors affecting cost will be the size of the barrier and the material from which it is constructed. There will be no installation costs for jersey barriers or planters because they are not anchored into the ground. Bollards will require installation. Costs for the different types of passive security barriers are summarized in Table 7 below.