66 Section 1 Introduction to Collision Repair
Copyright Goodheart-Willcox Co., Inc.
Target
The object a vehicle collides with is called the
target. The target can be at rest, or it can be in motion.
Targets at rest can have enough inertia that they will
not be moved by a collision. A bridge abutment is
an example of an unmovable target. The weight of
the abutment is so great that the impact force of any
vehicle cannot overcome it. Additionally, because the
abutment is solid concrete, it will not flex or give during
a collision. If a vehicle were to collide with the abut-
ment, all the force in the collision would be directed
back at the vehicle. None of the force would move or
distort the abutment.
A vehicle that hits a hard, unmovable target
will sustain more damage than a vehicle that hits a
movable target. When a vehicle hits a movable target,
some of the collision force is used to overcome the
inertia of the target, setting the target in motion. This
is energy that will not be directed back at the vehicle.
Some examples of targets that can be set in motion
include other vehicles, fence posts, guardrails, and
small trees. Some targets may also be in motion. If two
vehicles collide head on, the force of the collision is the
sum of the forces of each vehicle. If a vehicle crashes
into a target that is soft, some of the collision energy
will be used to deform the target. Therefore, not all the
collision energy will be directed back at the vehicle.
Impact Angle
The next collision factor to be considered is the
impact angle. Figure 4-16A shows an accident that
occurred after vehicle A ran a red light. The driver
of vehicle B attempted to stop and steer away from
vehicle A. The attempt was unsuccessful and a crash
resulted. Vehicle B impacted near the center of vehicle
A. The force from vehicle B distorted both vehicles and
pushed vehicle A sideways. The energy distribution
during the collision would be different if vehicle B hit
vehicle A away from the center. Figure 4-16B shows
vehicle B impacting near the front of vehicle A. Some
of the force is used to make vehicle A spin. Therefore,
less force is used to distort the vehicles. From this, you
can see that if the impact takes place at the vehicle’s
center, the damage will be greater than if the impact
takes place away from the center.
Surface Area of Impact
The next collision factor is the surface area of
impact. If the surface area of impact is large, the
collision force is spread out over a large area. If the
surface area of impact is small, the force is concen-
trated in a small area. Figure 4-17 shows how this
A B
A
B
A
B
Tree
Goodheart-Willcox Publisher
Figure 4-15. This vehicle slid sideways into a tree. The
center section of the vehicle was stopped by the tree.
The end sections continued moving, resulting in inertia
damage.
Goodheart-Willcox Publisher
Figure 4-16. A—If vehicle B hits vehicle A in the center
section, the end sections of vehicle A will distort as it
is pushed to the right. B—If vehicle B hits vehicle A on
one end, vehicle A will spin.