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3.1 Current U.S. Side Impact
Standard
On October 30, 1970, the Federal Motor
Vehicle Safety Standards (FMVSS) were modified by the addition of
Standard 214; Side Impact Strength - Passenger Cars [3].
The standard went into effect on January 1, 1973. The purpose of
the standard was to enhance side door strength to minimize the
safety hazards caused by intrusion into the passenger compartment
during a side impact. The test procedure required "quasi-static"
loading applied by a rigid steel cylinder or semicylinder.
Intermediate and peak crush force limits were established. This
"quasi-static" requirement was extended to trucks,
buses, and multipurpose passenger vehicles with a gross vehicle
weight rating (GVWR) below 4,535 kg (10,000 lbs), effective
September 1, 1993 [4]. The agency's 1982 evaluation of this
"quasi-static" requirement indicated that the standard
was effective in side impacts of single vehicles into fixed
objects but provided little benefit for occupants in vehicle-to-vehicle
collisions.
On October 30, 1990, a final rule was
published adding a dynamic impact requirement for passenger cars
to FMVSS 214; Side Impact Protection [5] to address
fatalities and injuries in vehicle-to-vehicle collisions. The
requirement was phased-in such that all passenger cars made after
September 1, 1996, had to comply. Subsequent to this action, a
final rule was published requiring all trucks, buses, and
multipurpose passenger vehicles under 2,721 kg (6000 lbs) to meet
the same dynamic impact requirement by September 1, 1998 [6].
The dynamic test procedure focused on the
measurement of anthropomorphic test dummy acceleration responses
that have been correlated with occupant injuries. A schematic of
the test configuration is shown in Figure 1. The dynamic test
simulates the 90 degree impact of a striking vehicle traveling 48.3
kph (30 mph) into a target (test) vehicle traveling 24.2 kph (15
mph). This is achieved by a moving deformable barrier (MDB), with
all wheels rotated 27 degrees (crab angle) from the longitudinal
axis, impacting a stationary test vehicle with a 54 kph (33.5 mph)
closing speed. For a typical passenger car, the left edge of the
MDB is 940 mm (37 in.) forward of the mid point of the struck
vehicle wheel base. The MDB has a total mass of 1367 kg (3015 lbs).
The aluminum honeycomb of the barrier face is specified by design.
The bottom edge of the MDB is 280 mm (11 in.) from the ground.
The protruding portion of the barrier simulating a bumper is 330
mm (13 in.) from the ground.
Figure 1 - FMVSS 214 Side Impact Test
Configuration. Linear dimensions are in inches, where 1
in. = 25.4 mm. |
The dimensions and material characteristics
of the MDB face are shown in Figure 2. This was initially derived
from the weights of passenger cars and lights trucks in the U.S.
fleet with a adjustment made assuming a downward trend in vehicle
mass due to fuel economy needs [7, pg IIIA-6].
Figure 2 - FMVSS 214 Side Impact Deformable
barrier Face. Linear dimensions are in inches, where 1 in.
= 25.4 mm. |
Side Impact Dummies (SID) are placed in
front and rear occupant positions on the side of the vehicle
which is being struck. The instrumented dummies must exhibit rib,
spine and pelvic accelerations below specified thresholds in
order to pass the test. The rib and spine accelerations are
combined into a single metric called the Thoracic Trauma Index (TTI(d))
which has an 85g limit for 4-door vehicles and a 90g limit for 2-door
vehicles. The pelvic acceleration has a 130g limit.
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