Stopping Car Bombs in their Tracks

From embassies and universities to transportation hubs and used car lots, a wide variety of organizations protect themselves from errant drivers and truck bomb threats with barriers, bollards, barricades and crash gates.

Think back to April 2010, in Peshawar, Pakistan. A Taliban bomber rammed his car into a police checkpost, killing five policemen; however, Peshawar police chief Liaquat Ali told Reuters that the attacker was apparently trying to make his way into the city but decided to set off his explosives when he was stopped by pedestrian gates. 

If one compares the destruction car and truck bombs have caused to the event in Peshawar, it is easy to discern that a large factor in saving lives from vehicle bombers is to successfully stop the attacking vehicle far enough away from a facility to avoid the high pressure shock wave of a bomb blast.

The U.S. Embassy in Jordan not only uses barriers to protect its compound from charging vehicles, but the barriers also create a sally-port which tightly controls traffic into the embassy. The first barricade is lowered to let in a car, while the barrier in front of the car stays up. The one in back then raises and the car is sandwiched between them. Once searched and permitted to pass, the second barricade lowers and the car is allowed to enter the embassy.

The bottom line is that terrorists typically do not go where they see barricades, so placing them in vulnerable spots reduces security risks dramatically — even if the need is only short-term.

Temporary barriers can protect facilities during events, such as a college football game or presidential visit, until permanent barriers are installed, and where physical conditions preclude permanent solutions, such as the State Department did to protect the embassy on Paris’ city streets.

 A High School Physics Reminder

To evaluate security risk for a given facility, pay attention to the weights and velocities of vehicles that could be used to penetrate the facility. A vehicle moving towards a barricade has a certain kinetic energy, which is the major measure of how much "hitting power" it possesses. Mathematically, kinetic energy is derived from the vehicle velocity and its weight (mass). On impact, some of this energy is converted to heat, sound and permanent deformation of the vehicle. The barricade must absorb the remainder of this energy if the vehicle is to be stopped.

The amount of remaining energy varies on many factors — primarily the velocity of the vehicle at the moment of impact. The amount of kinetic energy changes as the square of its velocity. For example, a vehicle moving at 50 mph has 25 times as much kinetic energy as it would at 10 mph. Thus, an armored car weighing 30 times as much as a Toyota Corolla and moving at 10 mph would have less hitting power than the Toyota moving at 60 mph.

Because of this, every effort must be made to force a vehicle to slow down before it reaches the barricade. The most frequently used technique is to require a sharp turn immediately in front of the barrier. When vehicle speed is reduced by 50 percent, the "hitting power" is reduced by four times. If the speed is reduced by 65 percent, the force of impact will be reduced by nine times.

Upon designing a way to slow down vehicle approach, precautions should also be taken so the attacking car cannot make a "corner cutting shot" at a barricade. Often, only a light post defines a turning point and a speeding car can take it out and not even hesitate. Knolls and other impediments should be considered. If the approach to the facility is long, it is best to create curves along the access roads as a natural obstacle to speeding cars or trucks.

Overcoming Common Design Deficiencies

No area is more critical to the vehicle barrier selection process than testing. Without adequate testing, there is no assurance that the barrier will resist the threat. Testing is normally by an independent testing company or government agency, such as the Department of State (DOS) and the military. Comprehensive reports of test results are issued and are available from the testing agency or manufacturer.

Today's barriers are capable of stopping and destroying a truck weighing up to 65,000 pounds and traveling at 50 mph. Such barricades can be raised or lowered at will to stop traffic or let it through. In an emergency, the thick steel plates or bollards pop out of the ground within one second.

A mobile barrier can be towed and set up in only 15 minutes. Nonetheless, it will stop a 15,000-pound (22.2 kN) vehicle going 40 mph (80 mph). For instance, deployable vehicle crash barriers helped the 4,000 police and military officers protecting participants at the Pittsburgh G-20 Summit. The totally self-contained barriers were towed into position and controlled vehicle access within 15 minutes. No excavation or sub-surface preparation was required. Once positioned, the mobile barricades unpacked themselves by using hydraulics to raise and lower themselves off their wheels. DC-powered pumps then raised or lowered the barriers.

In designing a barrier system, consider whether to use a passive or active system. Normally, an active system keeps the barrier in the active or up position. It must be deactivated to permit access. Active systems are preferable to ones that must be activated to prevent access because they are more secure.

One final area that should not be overlooked is aesthetics. With today's smart designs, it is no longer necessary to choose between form and function — end-users can have them both. Designers are creating secure environments with more compatible and aesthetically pleasing architectural elements.

Virtually unlimited in styles and aesthetics, safety consultants can specify having ornamental steel trim attached directly to a bollard or select cast aluminum, iron or bronze to slip over the crash tube. If damaged, the old sleeve simply slides off and a new one slips on. Designer bollards are available in stainless steel, cast stone, ceramics and epoxy-based stones. They can be fitted with an internal warning light for increased visibility and engineered to suit high traffic volumes.

In addition, highly customized designs can be added to the tops of bollards. For instance, those that protect California’s state capitol facilities in Sacramento include the Great Seal of the State of California, the Governor’s Seal, the Assembly Seal and the Senate Seal.

Bollard systems operate individually or in groups up to ten and are used for intermediate-level security applications. Individual bollards are up to 12.75 inches in diameter, up to 35 inches high and are usually mounted on 3-5 foot centers. Hydraulic versions can be operated by a variety of control systems. Manual versions are counter balanced and lock in the up or down position. They lower to allow passage of authorized vehicles. Bollards will stop vehicles dead in their tracks as they have been tested to stop and destroy an attacking vehicle weighing 10,000 pounds moving at 65 miles per hour or a 20,000-pound vehicle moving at 46 miles per hour.

High-security sliding gates, which will match the materials used in the perimeter fence, have been successfully full-scale tested to ASTM M50 and K12 standards, allowing no penetration of a 15,000 pound truck traveling 50 mph. Most customers want a shallow foundation to avoid underground utilities conflicts and significantly lower the time and cost of implementation.

For those organizations striving to create as green of an environment as possible, barriers, barricades, bollards and crash gates can be operated either manually or hydraulically on FDA-approved vegetable oils. There is also a growing trend to use electro-mechanical barricades.

David Dickinson is Senior Vice President, Delta Scientific