This appendix describes the following barrier types:
Natural and cosmetic barriers are effective if integrated into security planning, new construction, or renovation projects. Natural obstructions such as hills, outcroppings, lakes, and ponds can be used to stop, deter, or slow a vehicle trying to enter a facility. Natural materials, wood, dirt, and rock, can be used to build berms and walls that prove to be effective barriers, yet do not detract from the aesthetics of the site landscaping.
Factors to take into account include:
Vegetation
Vegetation along standoff zone perimeters and on off-road approaches to the perimeters can deter aggressors from approaching the protected facility from that route. Vegetation may also slow the approach of vehicles by providing obstacles to direct approach. Closely spaced plants in multiple, overlapping rows with trunk diameters greater than 5 inches are the best deterrents to stationary vehicles. Perimeter barriers capable of stopping moving vehicles can be integrated with plantings of vegetation for aesthetics purposes. Because mature plants are the most effective deterrents, the required plant material should be provided by retaining existing vegetation where possible.
Water
The effectiveness of bodies of water used as barriers to moving vehicles has not been quantified, but their value in slowing vehicles and as a deterrent is obvious. Water that is deep enough to submerge the exhaust pipes of vehicles will provide an effective barrier. Lesser depths may only slow vehicles. For example, cars and light trucks will be limited to speeds of approximately 25 miles per hour by large bodies of water only 6 inches deep. Bodies of water 3 feet deep would act as barriers to moving vehicles. If the body of water floor is uneven or contains several deep trenches, the effectiveness as a barrier increases significantly.
Terrain
Terrain features such as ditches, berms, hills, or large rocks may provide effective barriers to vehicles. Rocks or groups of rocks that have a collective mass equal to approximately twice that of the threatening vehicle make effective barriers. To be effective, rock ditches, and berms must span the approach route to block it. Those of lesser extent or such features of a size too small to stop a vehicle can be used as obstacles to slow vehicle approaches. In designing terrain obstacles, circuitous, off-road approach routes are far more effective than direct routes. As an example, the use of inclines can slow vehicle approaches by limiting their ability to accelerate.
The types of fabricated vehicle barriers include:
Concrete Barrier (Jersey Barrier)
Barriers can be erected from either precast tongue and groove sections or cast in place with special concrete-forming equipment. These barriers can be used around a fixed site as a perimeter vehicle barrier. Barriers can also be arranged to direct and slow traffic flow into a site. This gives the security personnel at the gate more time to react to a potential threat.
Portable Water/Sand-Filled Barriers
Plastic water or sand-filled barriers can be effective, as well as being easily moved without the need for heavy equipment.
Chain Link Gate Reinforcement
Wire ropes are fastened to gates and anchored on either side of the gate. For a relatively weak gate, the reinforcement transfers the force of a vehicle impact to a more substantial anchor system. It can be used on many different gate applications.
Cable Barrier
Cable is fastened to each post with U-clamps at a height of 30 inches and is periodically anchored. The cable is typically 3/4-inch diameter or larger aircraft cable mounted between chain link fabric and upright posts. The barrier prevents light vehicles from crashing through a standard chain link fence. One disadvantage is that the cable can be covertly cut when installed along the outermost perimeter.
Drum and Cable Barrier
Standard 55-gallon drums are filled with dirt, rock or concrete-weighing about 900 to 1,200 pounds-attached by a 3/4-inch aircraft cable to another drum or fixed object. Requires minimal setup time and expense. This can be a cost-effective application since empty storage drums, dirt and rock are readily available.
Dragnet
This consists of a chain link "net" assembly with arresting cables attached to an energy absorber that is attached to the anchor system. In the open position, the dragnet is suspended above the access road. When a vehicle hits the dragnet in the closed (dropped) position, the energy form the impact is transferred through the arresting cables to an energy absorber that brings the vehicle to a controlled stop.
Bollard
A bollard is a post made of concrete, stainless steel, aluminum, cast iron, or other durable material, that creates an aboveground obstacle. Bollards can be fixed or retractable. At the high end, bollards are constructed to completely stop most vehicles.
Removable Nuisance Barrier
A 3-inch pipe driven into the ground and fastened with 3/16-inch coil chain, is used to channel traffic and create marked isolation zones around sensitive areas, equipment, and buildings. It can be set up and removed quickly and easily.
Guardrail
Standard highway guardrails or median barriers; cable, W-beam, or box beam guardrails are used as a perimeter barrier. They are not designed to prevent head-on penetrations but can immobilize a lightweight vehicle attempting an intrusion.
Traffic Control Island with Vehicle Barriers
Standard guard post, with two automatic gates, a custom base, platform curb assembly with three pass-throughs, and 16 barrier posts provide protection for security personnel stationed at vehicle entrance.
Motorized Barricade
This refers to a steel barricade with standard height of 13 inches, and a maximum height of 30 inches. Several activation options are possible, such as by remote switch or card reader. These barricades provide a steel barrier that can be deployed to close off vehicle access in approximately three seconds.
Hydraulic Barricade
Upon major impact, the lifting mechanism absorbs the shock. In emergency situations, a steel barricade closes off vehicle access in just one second.
Electronic Barrier Gate
Chain link gates and turnstiles used for vehicle and personnel entrances, electronic barrier gates may be activated by remote switch, numerical code, or card reader.
Tire-Penetrating Traffic Barrier (One-way Tire Trendles)
A row of 3/8-inch steel teeth that are unidirectional, spring-loaded, are embedded in the road. The barrier punctures the tires of an intruding vehicle, while allowing passage of vehicles in the opposite direction.
Portable Roadblock Tire-Puncturing Device
Hollow stainless steel spikes mounted on aluminum scissors action arms expand to stretch across a vehicle access. Anchors hold the scissors in place. The system expands to cover 21 feet and folds into a case weighing 35 pounds. When an intruding vehicle passes over the system, the spikes imbed into the vehicle's tires and detach from the aluminum frame. This opens several "tubes" which cause rapid uniform deflation and prevent the holes from sealing. Since the air loss is uniform from all times, the operator is more likely to maintain control of their vehicle. These devices are most effective against light vehicles with standard 3/4-inch thick rubber tires.