Vehicle Arrestor. Absorbs virtually all of a vehicle's
and applies a low to moderate resistive force to gradually
stop a vehicle
over a relatively long distance. Examples are weights that
are dragged by
a vehicle and accumulate with distance traveled, and piles of
Crash Cushion. Absorbs a large portion of a vehicle's kinetic
energy and provides a stiff resistive force to stop a vehicle in a reasonable
distance. Examples are liquid-filled plastic containers and arrays of empty
steel barrels that are backed by strong supports.
Inertia Device. Exchanges momentum and kinetic energy with a
vehicle during impact. This device provides a stiff resistive force to stop
a vehicle in a reasonable distance. Examples are relatively small concrete
shapes and sand-filled barrels that are not anchored.
Rigid Device. Provides very high resistive force to stop
vehicles in very short distances. The vehicle dissipates almost all of its
own kinetic energy as it deforms during impact. Examples include massive
concrete shapes and steel structures that are well anchored.
The above general types of barriers may be active or passive.
Active barriers require action by personnel or equipment to permit entry.
Passive barriers can be used as traffic obstacles as shown in Figure 80.
Barriers may also be fixed, movable, or portable. Fixed barriers include
hydraulically operated rotating or retracting systems. Movable barriers
include 55-gallon (200-liter) drums, highway medians, etc. Portable barriers
include ropes, chains, and cables used as temporary barriers. In general,
all the above types of barriers have been designed and tested against
combinations of vehicle size, weight and velocity. Paragraph 8.2 shows that
the kinetic energy (KE) of such vehicles scales as the velocity squared;
hence reducing the velocity by a factor of 2 reduces the KE by a factor of 4.
Figures 81 and 82 (from the Army Security Engineering Manual) show the
effectiveness of both active and passive barriers against threats of various
KE. Figure 80 shows an example of one of the hydraulically activated
security plate type barriers. This barrier is 31 inches high and comes in a
standard width of 10 feet (other widths are also available). Normal
operation is 4 to 8 seconds (field-adjustable). This barrier has been crash
tested. A 14,980-pound (6,800-kg) vehicle traveling at a velocity of 50.3
mph (80 km/h) failed to penetrate the barrier. For further details on this
and other barriers shown in Figures 81 and 83, see the Navy Terrorist Vehicle
Bomb Survivability Manual. To use Figures 81 and 82, identify the vehicle
approach velocity and move upward to the curve associated with the vehicle
weight at the given threat severity. Read across to determine the kinetic
energy the barrier must resist. The kinetic energy capacities for the tested
barriers shown are indicated by horizontal lines. The barriers will stop any
kinetic energy below the associated horizontal lines. Vehicle barriers with
capacities below that required to stop the threat vehicle will probably
disable the vehicle, but the barrier will be penetrated. The vehicle will
then continue moving toward the