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1. SPECIAL ISSUE: CAR SIZE, WEIGHT, AND SAFETY
Vol. 44, No. 4, April 14, 2009
CAR
SIZE AND
WEIGHT
ARE CRUCIAL
to protecting people in crashes. One way to
see how crucial is to crash two cars that
have a lot in common other than their size
and weight differences. For example, crash
a microcar or a minicar with good frontal
crashworthiness ratings into a midsize
2. 2 Status Report, Vol. 44, No. 4, April 14, 2009
model that earns the same ratings and was manufactured by the same automaker. What happens ratings with those of midsize cars — or with
in the front-to-front collision says a lot about the safety consequences of vehicle size and weight. the ratings of cars in any other class, for that
The Institute recently crashed a Honda Fit into a Honda Accord, a Smart Fortwo into a Mer- matter, because of the effects of vehicle size
cedes C class, and a Toyota Yaris into a Toyota Camry (these automakers have micro and minicars and weight.”
rated good for frontal crashworthiness, based on the Institute’s 40 mph offset test into a de- The Institute didn’t choose SUVs or pick-
formable barrier). The car-to-car tests aren’t about whether one minicar is more crashworthy than ups, or even large cars, to pair with the minis
another. Such information is available from the comparative ratings based on the barrier tests. in the new crash tests. The choice of midsize
The new tests of paired cars are about the physics of crashes. Reflecting Newton’s laws of mo- cars reveals how much influence some extra
tion, the results confirm the lesson that bigger, heavier cars are safer (see facing page). Some mini- size and weight can have on crash outcomes.
cars earn higher crashworthiness ratings than others, but as a group these cars generally can’t Honda Accord versus Fit: The Accord
protect people in crashes as well as bigger, heavier models. came through the frontal test without signifi-
“There are good reasons people buy minicars,” says David Zuby, the Institute’s senior vice pres- cant downgrades. Measured intrusion at 8
ident for vehicle research. “For starters, they’re affordable, and they use less gas. But the safety locations in the occupant compartment was
trade-offs are clear from the results of our new tests.” in the good range, and all (continues on p.6)
MIDSIZE HONDA ACCORD: GOOD MINI HONDA FIT: POOR
As in the barrier tests the Institute conducts for consumer information, each of the cars in the The midsize Honda Accord’s occupant
frontal offset crashes involving pairs of 2009 models from Daimler, Honda, and Toyota were compartment remained intact during
going 40 mph. Researchers rated each car’s performance from good to poor based on measured this 40 mph frontal collision with the
intrusion into the occupant compartment, forces recorded on the Hybrid III driver dummy, and Fit, a minicar. In contrast, there was a
movement of the dummy during the impact. The main difference between these tests and those lot of intrusion into the Fit’s occupant
conducted for consumer information is the car-to-car versus car-into-barrier configuration. compartment, which compromised the
“Sometimes the whole issue of size and weight gets obscured in the quest to buy a car with survival space around the driver dummy.
good safety ratings,” Zuby says. “The ratings are important, but frontal ones can be used only Measures recorded on the dummy indicate
to compare cars that are similar in size and weight. You can compare the ratings of the Fit and that the risk of serious injury would be high
Yaris, for example, and find they both earn good overall scores. But you can’t compare these cars’ in a real-world collision similar to this test.
3. SIZE
When a car crashes into a solid barrier,
the outcome depends in part on the size of
the front end. If one car’s front end is long
enough to crush twice as much as another
car’s in a barrier crash at the same speed,
its restrained occupants will experience half
as much force as the people in the smaller car
because it takes them twice as long to stop.
LONGER CRUSH SPACE SHORTER
WEIGHT
When two cars going the same speed crash
3,600 LBS 1,800 LBS
front to front, the outcome depends in part
on the cars’ relative weights. The heavier car
will push the lighter car backward during the
impact, which means the velocity change of ONE OF THESE CARS WEIGHS TWICE AS MUCH AS
40 MPH 40 MPH THE OTHER. WHEN THEY COLLIDE, EACH GOING
the heavier car will be much less than that
40 MPH, THE HEAVY CAR PUSHES THE LIGHT ONE
of the lighter car. If the lighter car weighs BACKWARD AT 13 MPH. THE VELOCITY CHANGE
half as much as the heavier car, the forces OF THE LIGHT CAR (53 MPH) IS TWICE
on its occupants will be twice as great. THAT OF THE HEAVIER CAR (27 MPH).
PHYSICS
DICTATE CRASH OUTCOMES 13 MPH
The poor performance of all three micro and tance from the front of a vehicle to its occupant compartment. The longer this is, the lower the
minicars in frontal impacts with midsize cars forces on the occupants, provided vehicle designers take advantage of the extra length.
(see p.1) isn’t surprising. It reflects the laws of These two factors, size and weight, have separate effects, but they’re highly correlated. In
the physical universe, specifically principles theory the lighter weights of smaller cars could be offset by increasing the sizes of their front
related to force and distance. ends, keeping weight down by using materials like aluminum, plastic, or titanium. But this typically
Although the physics of frontal car crash- doesn’t occur because such materials cost so much.
es usually are described in terms of what hap- Characteristics including the stiffness of a vehicle’s front end also influence the outcomes of
pens to the vehicles, injuries depend on the crashes. However, size and weight are the basic influences.
forces that act on the occupants — and these Size and weight affect injury likelihood in all kinds of crashes. In a collision involving two vehicles
forces are affected by two key physical factors. that differ in size and weight, the people in the smaller, lighter vehicle will be at a disadvantage. The
One is the weight of a crashing vehicle, which bigger, heavier vehicle will push the smaller, lighter one backward during the impact. This means less
determines how much its velocity will change force on the occupants of the heavier vehicle and more on the people in the lighter vehicle. Greater
during impact. The greater the change in ve- force means greater risk, so the people in the smaller, lighter vehicle are more likely to be injured.
locity, the greater the forces on the people Crash statistics confirm this. The death rate in 1-3-year-old minicars involved in multiple-vehicle
inside and the higher the risk of injury. crashes during 2007 was almost twice as high as the rate in very large cars.
The second physical factor affecting injury “Some minicars are definitely more crashworthy than others,” says David Zuby, Institute senior
likelihood is vehicle size, specifically the dis- vice president for vehicle research. “So it pays to compare their safety ratings. But as a group mini-
4. 4 Status Report, Vol. 44, No. 4, April 14, 2009
cars do a comparatively poor job of protect-
ing people in crashes, simply because they’re FUEL ECONOMY AND SAFETY CAN
BE ACHIEVED AT THE SAME TIME
smaller and lighter. In collisions with bigger
vehicles, the forces acting on the smaller one
are higher, and there’s less distance from the
front of a small car to the occupant compart- One reason people buy smaller cars is to comply with federal standards (see Status Re-
ment to ‘ride down’ the impact. These and conserve fuel. The price of gasoline skyrock- port, April 6, 2002; on the web at iihs.org).
other factors increase injury likelihood.” eted last year, and there’s no telling what the A problem with the current structure of
Fatality risk in minicars is high in single- as price at the pump might be next week. fuel economy standards for cars is that the
well as multiple-vehicle crashes. The death Meanwhile, the gears are turning to hike fed- target of 27.5 miles per gallon is applied to an
rate per million 1-3-year-old minis in single- eral fuel economy requirements to address automaker’s whole fleet, no matter the mix of
vehicle crashes during 2007 was 35 compared environmental concerns. cars an individual automaker sells. This en-
with 11 per million for very large cars. Even in The conflict is that smaller vehicles use courages manufacturers to sell more smaller,
midsize cars, the death rate in single-vehicle less fuel but do a relatively poor job of pro- lighter cars to offset the fuel consumed by
crashes was 17 percent lower than in minicars. tecting their occupants in crashes (see p.3). their bigger, heavier models. Sometimes au-
Thus, fuel conservation policies have tended tomakers even sell the smaller — and less safe
to conflict with motor vehicle safety policies. — cars at a loss to ensure compliance with
DRIVER DEATHS PER MILLION But they don’t have to. fleetwide requirements.
1-3-YEAR-OLD CARS REGISTERED, 2007 “The key going forward will be for con- “What’s needed instead is to restructure
sumers and policymakers to recognize the fuel economy standards for cars the same as
■ multiple-vehicle potential conflict and make choices that serve the government has done for other kinds of
■ single-vehicle safety as well as fuel economy. The first step passenger vehicles,” Lund advises.
40
is to look at the consequences of past policies In 2006 the National Highway
and choose future ones that serve both goals Traffic Safety Administration
20 instead of setting the two at odds,” says adopted a fuel economy
Institute president Adrian Lund. system for SUVs, pickup
Fuel economy at the expense of safety: trucks, and vans that
mini small midsize large very large More than 30 years have elapsed since mandates lower fuel
Congress enacted the Energy Policy and Con- consumption as vehi-
Driver death rates decline fairly consistently servation Act of 1975, which required auto- cles get smaller and
as vehicle size increases. This doesn’t mean makers to build cars that use less fuel. The lighter, thus remov-
drivers have to choose the heaviest vehicles result during the first 15 or so years of this law ing the incentive for
on the road to reap safety benefits. New was to improve the overall fuel economy of automakers to downsize
crash tests demonstrate that midsize cars the US car fleet by about 75 percent. their lightest vehicles to com-
afford a lot more protection than minicars The main way automakers achieved this ply (see Status Report, April 22, 2006;
from the same manufacturer (see p.1). was by reducing car weights. For example, on the web at iihs.org). The result is to force
The overall driver death rate in midsize Chrysler stopped making big cars altogether. the auto manufacturers to use vehicle and
By 1985 cars were an average of 500 pounds engine technologies to improve fuel economy.
cars is 23 percent lower than in minicars.
lighter than they would have been without the By 2011 all SUVs, pickup trucks, and vans will
federal requirements. have to comply.
“The lower death rates in single-vehicle The downside was to increase fatality risk However, the same plan doesn’t yet apply
crashes of larger cars are because many ob- in crashes. Multiple studies document this, to cars, which still are subject to a fleetwide
jects that vehicles hit aren’t solid, and big, including Institute research comparing deaths fuel economy standard. The Bush administra-
heavy vehicles have a better chance of mov- in Ford and General Motors cars before and tion proposed a size-based standard for cars,
ing or deforming the objects they strike. This after they were downsized during 1977-86 (see like the other passenger vehicles, but left it
dissipates some of the energy of the impact,” Status Report, Sept. 8, 1990; on the web at iihs. to the current administration to carry through.
Zuby explains. org). The finding was a 23 percent increase in Now the Obama administration says it’s boost-
Insurance claims filed for injuries under per- deaths per 10,000 registered cars. ing the fuel economy standard for cars,
sonal injury protection coverage also are higher Subsequent research documents the continu- beginning with 2011 models, and this will be
for minis than for midsize cars. Overall losses, ing price in terms of lives. For example, the Na- accomplished under a size-based system.
which reflect both claim frequency and severity, tional Research Council concluded in 2002 that On a separate front, California officials are
are 193 for 4-door minis versus 147 for 4-door 1,300 to 2,600 additional crash deaths occurred trying to improve air quality by setting more
midsize cars (100 is the average for all cars). in 1993 because of vehicle weight reductions to stringent emissions limits than the federal gov-
5. Status Report, Vol. 44, No. 4, April 14, 2009 5
ernment requires. The state’s carbon emis- 46,402 in 1974. The National Research Council “Drivers don’t have to wait for the govern-
sions limit is structured so that vehicles of all estimated that most of the reduction was due ment to act. They can simply choose to drive
sizes would be held to a single average, which to the lower speed limit, and the rest was be- slower or choose to buy cars that aren’t the
conflicts with occupant safety goals. cause of reduced travel. By 1983 the national smallest ones available but still earn kudos for
A US Court of Appeals is considering maximum 55 mph limit still was saving 2,000 fuel economy,” Lund points out. For example,
whether federal fuel economy standards pre- to 4,000 lives annually. the Honda Civic Hybrid and Toyota Prius, also
empt California’s emissions standard, and the With the oil crisis a thing of the past by the a hybrid, get better gas mileage than the Smart
Institute has filed a brief opposing the state. middle of the 1980s, Congress lifted pressure Fortwo. Even the Volkswagen Jetta with a
The problem, the Institute told the court, is on states to retain 55. Speed limits began diesel engine does almost as well.
that “the easiest, cheapest, and quickest way going up in 1987, and so did occupant deaths There are other ways, both individual and
for automakers to meet a significant reduction in crashes. Fifteen to 30 percent increases societal, to serve fuel economy and safety
in an overall fleet average of carbon emissions were documented. simultaneously. For example, roundabouts
is to downsize to reduce fuel consumption,” “The national maximum speed limit was serve both at intersections (see Status Report,
which costs lives in crashes. Lund adds that adopted to save fuel, but it turned out to be June 9, 2008; on the web at iihs.org). The key
if a state does succeed in preempting fed- one of the most dramatic safety successes in going forward is to keep the potential conflict
eral fuel economy or emissions standards, it motor vehicle history,” Lund points out. “The between safety and fuel conservation in mind
should ensure that its programs don’t so that policies designed
have negative consequen- to serve one don’t in-
ces for people advertently compro-
in crashes. mise the other.
Travel speeds affect both: political will to reinstate it probably ONE OF THESE CARS
Setting higher federal fuel econo- is lacking, but if policymakers want a IS BIGGER THAN THE OTHER,
my targets isn’t the only way to con- win-win approach, this is it. It saves fuel but this doesn’t mean their fuel economy
serve fuel. How about lowering speed limits? and lives at the same time.” necessarily varies by as much as their size
Going slower uses less fuel to cover the same More good choices going forward: Another difference suggests. Some models that are
distance. There’s a big safety bonus, too, way to serve both safety and fuel economy classified as small or even midsize get as
that’s evident in the experience of the 1970- would be to curtail the horsepower race. Only many miles to the gallon, or almost as
80s (see Status Report, Nov. 22, 2003; on the a few cars used to be capable of 300 horsepow- many, as cars classified as minis. The
web at iihs.org). er, but now many cars match this. Average safety plus is that death rates are lower
Goaded by federal lawmakers, every state horsepower is 70 percent higher than it was
in the larger cars (see chart, facing page).
adopted 55 mph speed limits on interstate in the mid-1980s, and some of today’s high-
So driving a relatively big car that’s also
highways in 1974. The impetus was the 1973 performance cars surpass the power of even the
economical on fuel is one way to serve both
oil embargo, and the idea was to conserve fuel muscle cars of the 1960-70s. If an automaker
by slowing down motorists until automakers were forced to use engine-enhancing technology safety and fuel conservation. Another way
could build cars that use less gas. The imme- to improve fuel efficiency instead of to boost per- is for state and local officials to set and
diate effect was to save thousands of barrels formance, safety would improve, too, because enforce lower speed limits. Going slower
of fuel per day — and thousands of lives. In vehicles with souped-up horsepower are asso- uses less gas to cover the same distance,
fact, highway deaths declined about 20 per- ciated with increased injury risk (see Status and it reduces both crash likelihood and
cent the first year, from 55,511 in 1973 to Report, April 22, 2006; on the web at iihs.org). the severity of the crashes that occur.
6. 6 Status Report, Vol. 44, No. 4, April 14, 2009
tion of the Smart’s poor performance but not
the only one. There was extensive intrusion
into the space around the dummy from head
to feet. The instrument panel moved up and
toward the dummy. The steering wheel was
displaced upward. Multiple measures of
injury likelihood, including those on the
dummy’s head, were poor, as were
measures on both legs.
“The Smart is the smallest car we
tested, so it’s not surprising that its
performance looked worse than the
Fit’s. Still both fall into the poor
category, and it’s hard to distin-
guish between poor and poorer,”
Zuby says. “In both the Smart
and Fit, occupants would be sub-
ject to high injury risk in crashes
with heavier cars.”
In contrast, the C class held up well,
with little to no intrusion into the occupant
compartment. Nearly all measures of injury
likelihood were in the good range, though the
(continued from p.2) except one measure of measure on the head was downgraded to ac-
injury likelihood recorded on the driver ceptable because the dummy’s head struck
dummy’s head, neck, chest, and both legs the B-pillar hard. Still, this was a good per-
also were good. Only the value recorded on formance overall.
the left foot veered from good into the accept- Toyota Camry versus Yaris: There was far
able range (values are based on thresholds more intrusion into the compartment of the
indicating injury likelihood). Yaris than the Camry. The minicar’s door was
In contrast, a number of injury measures largely torn away. The driver seats in both
on the dummy in the Fit were less than good. cars tipped forward, but only in the Yaris did
Forces on the left lower leg and right upper the steering wheel move excessively.
leg were in the marginal range, while the Similar contrasts characterize the measures
measure on the right tibia was poor. These of injury likelihood recorded on the dummies.
indicate a high risk of leg injury in a real-world The heads of both struck the cars’ steering
crash of similar severity. In addition, the wheels through the airbags, but only the head
SMART INTO C CLASS: POOR dummy’s head struck the steering wheel injury measure on the dummy in the Yaris
through the airbag. rated poor. There was extensive force on the
Intrusion into the Fit’s occupant compart- neck and right leg plus a deep gash at the
The space around the driver dummy in the ment was extensive at 6 of 8 measured loca- right knee of the dummy in the minicar.
Smart Fortwo collapsed during a 40 mph tions, warranting a marginal rating for the Like the Smart and Fit, the Yaris earns an
frontal offset crash test into a Mercedes structure. Overall, the Fit is rated poor in this overall rating of poor in the car-to-car test.
C class. Multiple injuries, including to front-to-front test, despite its good crashwor- The Camry is acceptable, which doesn’t
the head, would be likely for a real-world thiness rating based on the Institute’s offset match its good rating in the Institute’s 40 mph
driver of a Smart in a similar collision. barrier test. The Accord earns good ratings barrier test, despite the similar speed and off-
This outcome contrasts with the Smart’s for performance in both tests. set configuration (see facing page). Still the
performance in the Institute’s frontal offset Mercedes C class versus Smart: After strik- midsize car fared much better than the mini.
barrier test that’s run at the same 40 mph ing the front of the C class, the Smart went air- Laws of physics prevail: Some propo-
speed. In the barrier test, the Smart earned borne and turned around 450 degrees. This nents of mini and small cars claim they’re as
a good rating overall, while it rates poor contributed to excessive movement of the safe as bigger, heavier cars. But the claims
in the collision with the C class. dummy during rebound — a dramatic indica- don’t hold up. For example, there’s a claim
7. TOYOTA CAMRY: ACCEPTABLE TOYOTA YARIS: POOR
that the addition of safety features to the
smallest cars in recent years reduces injury
risk, and this is true as far as it goes. Airbags,
advanced belts, electronic stability control,
and other features are helping. The same fea-
tures have been added to cars of all sizes,
though, so the smallest cars still don’t match
bigger ones in terms of occupant protection.
Would hazards be reduced if all passenger
vehicles were as small as the smallest ones?
Yes, this would help in vehicle-to-vehicle
crashes, but occupants of smaller cars are at
increased risk in all kinds of crashes, not just
collisions with heavier passenger vehicles.
Almost half of all crash deaths in minicars YARIS IN BARRIER TEST: GOOD YARIS INTO CAMRY: POOR
occur in single-vehicle crashes, and these
deaths wouldn’t be reduced if all cars became
smaller and lighter. In fact, the result would be BARRIER TEST VS. CAR TO CAR: Car-to-car crash tests often are more demanding than the front-
to afford less occupant protection fleetwide in into-barrier tests the Institute conducts for consumer information (go to iihs.org/ratings). A basic
single-vehicle crashes. reason is that the barrier test mimics a frontal crash between identical cars — a Toyota Yaris into
Yet another claim is that minicars are easier a Yaris, for example. Because the midsize Toyota Camry weighs more than the Yaris, it inflicted
to maneuver than big cars, so their drivers can more force on the minicar, compared with a barrier test.
avoid crashes in the first place. Insurance Drivers of minicars aren’t likely to confine their crash experience to other minis. As the smallest
claims experience says otherwise. The frequen- cars on the road, they’re far more likely to collide with bigger, heavier vehicles. This is when the
cy of claims filed for crash damage is higher for safety consequences resemble those in the crash with the Camry — or worse.
mini 4-door cars than for midsize ones. Another consideration is that, while the Institute’s barrier approximates the front of another car, it
There’s no getting around the laws of the can’t be designed to mimic the various fronts of hundreds of different cars. This helps explain why
physical universe. The Institute’s new crash the Camry performed worse in the test with the Yaris than in the barrier impact that approximated
tests confirm this — again. a crash with another Camry — something about the Yaris’ front end was more difficult to manage.
8. NON-PROFIT ORG.
U.S. POSTAGE
PAID
PERMIT NO. 252
ARLINGTON, VA
1005 N. Glebe Rd., Arlington, VA 22201
Phone 703/247-1500 Fax 247-1588
Internet: www.iihs.org
Vol. 44, No. 4, April 14, 2009
SPECIAL ISSUE
CAR SIZE & WEIGHT, AGAIN: The new series
of crashes involving mini and midsize cars
isn’t the Institute’s first foray into testing to
demonstrate vehicle size and weight effects
in frontal crashes. The first time was in 1971,
and the test series featured an AMC Gremlin
(above left) then known as an economy car,
crashing into AMC’s large Ambassador model.
Contents may be republished with attribution.
This publication is printed on recycled paper.
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