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SCORE ARCHIVES
On Average 6,714 Fewer People Died Each Year in the U.S. since 2005 Due to Safer Vehicles!
Since 2005, very significant improvements in automobile crashworthiness design have resulted in dramatic reductions in highway fatalities and injuries. After a decade when traffic fatalities remained at a nearly consistent 42,000 annually, the numbers began a downward trend in 2005, and declined to 32,000 by 2011. Had the 2004 fatality rate been constant rather than declining over the 2005-2011 period, 52,000 more people would have died. These dramatic reductions in deaths can be directly attributed to improved vehicle crashworthiness. After accounting for a reduction of approximately 5,000 fewer drunk driving related deaths during this period, the remaining 47,000 people are alive today because their vehicle was safer than the vehicle they drove 7 years ago as demonstrated by the reductions in risk index SCORE levels over this period.
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. Risk Index SCORE (Statistical Combination Of Risk Elements)
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2003 - 2010 Vehicle risk index SCOREs (updated 3/8/11):
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The risk index SCORE, published on this website since 2003, was the best overall metric for comparing the safety of vehicle design and combines ratings from both NHTSA and IIHS into a single risk value. The dramatic reduction in the average SCORE for each successive new model-year since 2005 was an excellent predictor of the reduction in highway fatalities that were realized, as newer, “safer” vehicles were progressively introduced into the mix of vehicles on the highways. . The graph, below, shows the actual U.S. traffic fatality counts compared with the average calculated risk index SCOREs. . . .
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. The SCORE for any vehicle is a calculated value that combines 10 known risk elements on the basis of their weighted contribution towards traffic fatalities. These risk elements utilize all known, validated measurements pertaining to vehicle safety, and are comprised of:
Weighting Risk Based on Fatality Modes
The SCORE combines the elements of risk, on a weighted basis, in proportion to U.S traffic fatalities: Frontal Impact (52%) + Side Impact (27%) + Rollover (17%) + Rear Impact (4%), [52+27+17+4] = 100. Vehicle SCOREs are therefore proportional to the relative fatality risk between vehicles.
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CONSUMER ALERT:
sPrimary Fundamental Shortcomings of NHTSA and IIHS Rating Systems
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Fatality rates in some vehicles are more than 20x higher than others. Consumers determined to learn which vehicles are safest, and who seek guidance from NHTSA and IIHS crash-test ratings, often find it very difficult to utilize these resources effectively, primarily for the following reasons:
(1) Omission by both agencies to factor into their ratings the significant role of vehicle weight in multi-vehicle collisions. Although both agencies warn consumers not to compare frontal crash test results between vehicles varying more than 250 lbs. they do not provide guidance on how you should consider weight.
(2) Lack of risk apportionment based on the relative importance of each rating category. For example, IIHS presents ratings for frontal, side and rear impact, however 52% of fatalities are associated with frontal impact vs. 27% for side, vs. only 4% for rear, leaving interpretation of the ratings to the consumer. Prior to model year 2011 NHTSA also presented individual ratings (frontal and side impact and rollover risk) without integrating them. However, commencing with model year 2011, NHTSA's new rating system combines these risks into an 'Overall Vehicle Score' (click here for detailed description of NHTSA's new rating system for 2011). [While this change for 2011 is an improvement the new rating system still fails to include the effects of vehicle weight and also ignores the IIHS ratings.]
(3) Both NHTSA and IIHS lump vehicles into very broad rating categories --- For example, 94% of 2010 model year vehicles received the best possible frontal rating, “GOOD” by IIHS and 99% received either 5-stars or 4-stars by NHTSA. This incorrectly portrays all of these vehicles to be equivalently safe.
(4) Virtually no recognition by either agency that the other agency exists. The frontal and side impact ratings of these agencies complement each other due to substantial differences in testing protocols, whereas some risk categories are only addressed by a single agency, e.g., only NHTSA rates rollover and only IIHS rates rear impact risk.
The SCORE (Statistical Combination Of Risk Elements) was created to address the above deficiencies by utilizing a mathematical model to combine, on a fatality-weighted basis, all available, quantifiable, validated data published by NHTSA and IIHS, to derive a single, overall measure of fatality risk.
The SCORE addresses all 4 deficiencies:
(1) The SCORE combines the fatality risk due to vehicle weight with the fatality risk measured by frontal crash testing, to derive the total frontal risk, which enables comparison between vehicles in different weight classes. Vehicle weight risk is shown in the chart, below, which is based on IIHS's regression analysis showing the correlation between vehicle weight vs. driver fatality rate in multi-vehicle collisions between passenger cars. Their analysis shows, for example, that a 2600 lb. passenger car has 2x the driver fatality rate vs. a 4000 lb. car, in multi-vehicle frontal collisions.
(2) In order to assign the appropriate risk contribution for each category of rating (frontal, rollover, side, and rear), the SCORE combines ratings in proportion to their total fatalities (52% frontal: 17% rollover: 27% side: 4% rear).
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Selecting the Safest Vehicles
There are three basic components to vehicle safety, and all three are readily quantifiable: (1) accident avoidance, (2) crashworthiness, and (3) vehicle incompatibility. In order to evaluate overall safety all three components must be combined in a statistically meaningful way, and by using actual traffic fatality data it is possible to assign the appropriate “weight” to each of these components.
Accident avoidance includes agility or maneuverability and is indirectly measured by rollover resistance, as determined by NHTSA. Electronic Stability Control can reduce the risk of rollover by helping to avoid the out-of-control conditions which often trigger a rollover, and must be considered when evaluating risk.
Crashworthiness, as measured by crash test ratings provided by NHTSA and IIHS, can be subdivided and weighted according to traffic fatalities in each crash mode (frontal, side and rear impacts).
The 3rd component, vehicle incompatibility, is an important consideration since 52% of all traffic accidents involve more than one vehicle, and the laws of physics give the advantage to the heavier vehicle. The relationship between vehicle weight and fatality rate is well documented and must be included in any overall assessment of safety. Heavy vehicles have reduced fatality risk in multiple vehicle accidents compared with light vehicles, however additional weight is not necessarily beneficial since heavier vehicles, especially SUVs and pickups, tend to ride higher above the ground with an attendant higher risk of rollover.
Only by combining all three components, and their elements, on a fatality-weighted basis, can overall fatality risk be compared between vehicles.
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Vehicle Age
Generally, the older the vehicle the less likely it is that rollover stability testing and comprehensive crash testing were conducted, and therefore your ability to screen those vehicles is limited. For example, prior to 2003 IIHS did not rate vehicles for side impact, nor did NHTSA prior to 1997. Also, prior to 2004, NHTSA did not perform dynamic stability testing on vehicles to evaluate tipping resistance.
Over the past decade manufacturers have greatly improved the crashworthiness of vehicles, and the availability of certain very effective safety equipment has greatly increased since 2003, including side-curtain airbags and Electronic Stability Control (ESC). Therefore, recent model vehicles are generally "safer" than older vehicles. For example, vehicles with risk index SCORES under 65 represent 21%, 30%, 18%, 16%, 6%, 5%, 3%, and 1% of all vehicles for model years '10, '09, '08, '07, 06, '05, 04, and '03, respectively. This improvement in vehicle safety may have contributed to the 29% decline in driver death rate over this same period of time
To evaluate vehicle safety for model years prior to 2003 your best resource is actual fatality rates. The "safest" vehicles can be considered to have demonstrated fatality rates less than 1/2 the average fatality rate (i.e., under 45 driver deaths per million vehicle-years), and represent approximately 15% of all vehicles.
Predicting Fatality Rates
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The best indicator of the predictive value for any measurement system is past performance. By applying the SCORE calculation to prior model-year vehicles for which fatality data have been compiled, the degree to which a vehicle's SCORE correlates to its real-world fatality rates can be observed.
The most recent data available on actual traffic fatalities has been published by IIHS, "Fatality Facts 2009", which provides driver fatality rates by vehicle class for model years 2007 - 2009. As you see from the plot below the risk index SCORE demonstrates a very significant correlation with actual fatality data for size/weight classes of vehicles.
The original evaluation of the risk index SCORE was made based on IIHS's 2005 status report "The Risk of Dying". In this report driver fatality rate data are provided for 199, 1999-2002 model year vehicles, for which statistically significant crash test rating data are available to enable meaningful SCORE calculations. As can be observed from the data plot below, a significant correlation does exist. This is not the case when attempting to correlate individual risk factors, such as IIHS's frontal impact rating, or NHTSA's frontal impact rating or vehicle weight (see the Elements of Risk page). Only through combining these risk elements in a weighted manner does a significant correlation appear. [2]
. NHTSA and IIHS Ratings Data provided by NHTSA and IIHS enable comparison between the average passenger car risk and any specific vehicle's risk, for each fatality mode. For example, if a vehicle (call it vehicle XYZ) receives "average" SCOREs for testing in all modes except rollover, which was determined by NHTSA to have 24% risk of rollover (vs. the average passenger car which NHTSA determined has a rollover risk of 12%) then the rollover element of risk for vehicle XYZ is considered to be double, i.e., 24%/12% = 2.0. Therefore, since rollover fatalities account for 17% of all fatalities, the rollover element for vehicle XYZ would be 2.0 x 17 = 34, and the SCORE would then be calculated as: Vehicle XYZ SCORE = {52 + 27 + 34+ 4} = 117. By comparing a vehicle's ratings for each of the 10 risk elements vs. the "average" passenger car it is possible to calculate the combined fatality risk for any vehicle, compared with the "average" passenger car. Since very few vehicles have been rated in all risk modes it is necessary that the SCORE system accommodate missing data by filling the blanks using the "average" value for that missing data. This results in a concentration of vehicles with SCOREs near the average vehicles' SCORE (100). [Note that the SCORE = 100 is actually the median SCORE for model-year 2005 passenger cars, whereas for model year 2011 the median SCORE is approximately 70.] Commencing with model year 2011 NHTSA's rating system was revised, so no direct comparison with their previous ratings is possible. This significant reduction in overall risk for newer vehicles may be attributed to a combination of improved crashworthiness, reduced rollover risk and the introduction of Electronic Stability Control and Side-Curtain Airbags.
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Comment about NHTSA's model year 2011/2012/2013 ratings: . 2011/2012/2013 vehicle SCOREs are not directly comparable with SCOREs for pre-2011 vehicles! Commencing with model year 2011 vehicles NHTSA has modified their rating system and therefore comparison with ratings for prior model year vehicles is not possible. The new system changes test dummies, measurements, risks of injury scales and has added a new side pole test. Also, the fatality mode distribution utilized by the risk index SCORE calculation, has been updated.
View the following listings using Adobe Acrobat (download here if needed)
. 4 STEPS TO SELECTING THE SAFEST VEHICLES:
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STEP 4: CONFIRM SIDE-CURTAIN AIRBAGS & ESC .
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The Elements of Risks
The risk index SCORE is comprised of the following risk elements, and each element is described below.
(I) Frontal impact
(I) Frontal Impact
a. NHTSA Frontal Ratings (for model years prior to 2011)
Because of the high incidence of front-end accident caused deaths NHTSA[1] began its crash testing program in 1978 to evaluate vehicles for frontal crashes. They use crash-test dummies representing an average-sized adult placed in driver and front passenger seats and secured with the vehicle’s seat belts.[2] . Vehicles are crashed into a fixed barrier at 35 miles per hour, which is equivalent to a head-on collision between two similar vehicles each moving at 35 mph. Instruments measure the force of impact to each dummy’s head, neck, chest, pelvis, legs, and feet. Frontal star ratings indicate the chance of a serious head and chest injury to the driver and right front seat passenger. A serious injury is one requiring immediate hospitalization and may be life threatening. . NHTSA’s rating scale is shown below. One significant observation is that small changes in the number of stars represent large differences in risk. This point is overlooked by many people, who apparently never read the definition of these ratings. Some people mistakenly believe that a four star rating is 4/5ths as good as a five star rating – whereas the average risk for 4-stars (15%) is actually 3x the average risk vs. 5-stars (5%).
NHTSA Frontal Crash ratings represent Risk of Serious Injury
. It is reasonable to expect to see a strong correlation between the NHTSA frontal crash test ratings and driver fatality rates, i.e., vehicles with high star ratings generally experiencing lower fatality rates than those with low star ratings, however this is not the case based on the driver fatality rates for approximately 200, 2002 vehicles[3]. The data plot shown below does not indicate any significant correlation between driver side frontal crash star rating and driver death rate, which appears to defy logic, but should be interpreted as demonstration that there are many elements which comprise the causes for the 30:1 variation in driver death rates from vehicle-to-vehicle. This observation reinforces the principle that many safety elements must be included to predict vehicle safety and selecting a single variable, as logical as it may appear, is inadequate as a safety screening method.
b. NHTSA Frontal Ratings (for model years 2011+)
For the upgraded frontal crash tests, crash-rating dummies representing an average-sized adult male and a small-sized adult female are placed in the driver and front passenger seats, respectively, and are secured with the vehicle's seat belts. Vehicles are crashed into a fixed barrier at 35 miles per hour (mph), which is equivalent to a head-on collision between two similar vehicles each moving at 35 mph. Since the rating reflects a crash between two similar vehicles, make sure you compare vehicles from the same weight class, plus or minus 250 lbs., when looking at frontal crash star ratings and Overall Vehicle Scores.
c. IIHS Frontal Rating
Although NHTSA frontal ratings provide useful frontal crashworthiness indicators, they are not the only considerations for evaluating front-end collision crashworthiness. NHTSA’s frontal test crashes the full width of the front of a vehicle into a rigid barrier. This maximizes the energy absorbed by the front of the vehicle so the occupant compartment is more likely to remain intact than if the same collision occurred hitting a smaller portion of the test vehicle, thereby concentrating the impact forces. . IIHS conducts an offset frontal crash test, where only the driver’s side of a vehicle’s front end is hit, so a smaller area of the structure is available to absorb the energy from the crash. Offset crashes are more demanding on the structure of a vehicle. IIHS conducts its offset test at 40 mph and only 40 percent of the total width of each vehicle strikes a barrier on the driver side. The barrier is constructed of aluminum honeycomb, which simulates the rigidity of another vehicle, so that the forces developed in the test approximate two vehicles of the same weight, colliding at approximately 40 mph. . IIHS has been performing offset frontal crash tests since 1995 and they use a qualitative rating system consisting of 4 scores: GOOD, ACCEPTABLE, MARGINAL, and POOR. For offset impact evaluation they derive an overall crashworthiness rating based on structural performance, injury measurements, and restraints/dummy kinematics. . In February 2004 IIHS published a report[4] showing the results of their statistical correlation between traffic fatalities which occurred over a 10-year period and the offset frontal ratings which had been assigned to vehicles resulting from IIHS’s offset frontal test. . Note in the figure below that the risk of fatality is 4 times greater in a vehicle rated “POOR” vs. “GOOD”.
. Despite the 4-to1 variation in fatality rates explained by IIHS frontal ratings, when IIHS frontal ratings are compared with fatality rates for individual vehicles (see plot below) there appears to be only a weak correlation. This is the same conclusion was reached when evaluating the NHTSA frontal crash ratings and emphasizes that there are other significant risk elements which are contributing to fatalities.
In order to combine the frontal impact ratings provided by NHTSA and IIHS the SCORE assumes equal weight to each agency's ratings. Therefore, since frontal impacts are responsible for 38% of all U.S. traffic fatalities (i.e., 38 points out of 100), the SCORE allocates 19 points to IIHS and 19 points to NHTSA (which is further subdivided into 9.5 points for NHTSA's driver rating and 9.5 points for NHTSA's front passenger rating).
* * (II) Vehicle Weight Class
Fatality data[11] show that 57% of all fatal crashes involve more than one vehicle. The laws of physics require that the momentum of the heavier vehicle impart higher deceleration forces to the lighter vehicle and experience correspondingly slower deceleration itself. Consequently, the occupants of the lighter vehicle experience larger forces. This is why both IIHS and NHTSA advise not to compare frontal crash ratings for vehicles of different weights. Accordingly, when two vehicles have identical frontal crash ratings, the heavier vehicle generally is safer than the lighter one. Fatality data demonstrate this to be the case and in a head-on collision a 1 percent weight advantage corresponds to more than a 5 percent reduction in the driver’s fatality risk, relative to the driver of the lighter vehicle.[12] [click here to see IIHS's report on vehicle Incompatibility]. . By examining fatality data in 2-vehicle fatal accidents, provided by the NHTSA’s Fatality Analysis and Reporting System[13], it is noted that there is an inverse correlation between weight and fatalities (i.e., more weight is associated with lower fatalities), as would be expected from the laws of physics. The SCORE utilizes these data by factoring the frontal impact risk by the ratio of driver death rate for a particular vehicle's weight divided by the driver death rate for the average (3,300 lb.) passenger car. The 41 driver deaths per million vehicle-years associated with the average weight passenger car (see plot below) is therefore representative of the average number of frontal impact driver fatalities. In the real world a vehicle's weight has the effect of amplifying or attenuating the risks obtained from crash test ratings, and since 57% of all frontal collisions involve more than one vehicle, weight is a significant risk factor. . The weight risk factor for heavy vehicles has the effect of offsetting frontal impact risk, derived from crash test data alone. For example, an "average" (3,300 lb.) passenger car with "average" frontal crash test ratings (4-1/2 stars by NHTSA + "ACCEPTABLE" by IIHS) has the equivalent SCORE as a 2,500 lb. passenger car rated 5-stars by NHTSA + "GOOD" by IIHS. In effect the improved crash test ratings compensated for the lighter weight, and the driver fatality rate stayed the same. This is the reason both NHTSA and IIHS warn consumers to only compare frontal impact ratings between vehicles within +/- 200 lbs of each other. Unfortunately, these agencies don't give you the guidance to compare the relative safety of vehicles in different weight classes. The SCORE utilizes the weight fatality ratio (vehicle fatality rate divided by the average passenger car fatality rate) to modify the frontal crashworthiness risk obtained from crash test ratings alone. Total frontal impact fatality = weight fatality ratio x crashworthiness fatality rate.
Similar to the discussion of frontal impact crash test ratings the raw data plot, below, does not show significant correlation between vehicle weight and driver fatality rates, based on driver fatality rates for approximately 200, model year 2002 vehicles[13]. Again, this provides further evidence that there are many elements which comprise the causes for the 30:1 variation in driver death rates from vehicle-to-vehicle, and selecting a single variable, as logical as it may appear, is inadequate as a safety screening method.
* * (III) Side Impact
a. NHTSA Side Ratings (model years prior to 2011)
In frontal impacts, the vehicle’s front-end structural volume behaves as an effective crumple zone, to absorb impact energy thereby decelerating the vehicle. Side impact, however, typically has much less crumple zone available, making side protection fundamentally a greater engineering challenge. Beginning in 1997, NHTSA began testing vehicles for side impact, using crash-test dummies representing an average-sized adult placed in the driver and rear passenger seat (driver’s side) and secured with the vehicle’s seat belts. The side crash test represents an intersection-type collision with a 3,015 lb. barrier moving at 38.5 mph into a standing vehicle. The moving barrier is covered with material that has “give” to replicate the front of a vehicle. Instruments measure the force of impact to each dummy’s head, neck, chest, and pelvis. .
. Head injury is not currently included in NHTSA’s star rating. This is a significant shortcoming, since some vehicles may receive high star ratings yet may expose the occupants to serious or fatal head injuries. As you will see below, IIHS’s side impact rating is necessary to evaluate risk of head injury.
Note that small changes in the number of stars for NHTSA’s side impact ratings represent large differences in risk, similar to what was observed for frontal impact star ratings. . b. NHTSA Side Ratings (model years 2011+)
For the upgraded side barrier crash tests, crash-rating dummies representing an average-sized adult male and a small-sized adult female are placed in the driver and rear passenger seats (driver's side), respectively, and are secured with the vehicle's seat belts. The side crash rating represents an intersection-type collision with a 3,015 pound barrier moving at 38.5 mph into a standing vehicle. The moving barrier is covered with material that has "give" to replicate the front of a vehicle. Since all rated vehicles are impacted by the same size barrier, it is possible to compare all vehicles with each other when looking at side barrier crash protection ratings. . . Lower spine injury for the front seat occupants, although measured, is not currently included in the star rating. An excessive lower spine injury reading (lower spine reading greater than 82 Gs) is reported separately as a safety concern. Star ratings for front and rear seat occupants in the side barrier crash test are assigned as follows:
c. NHTSA's 2011 new side pole crash test and ratings
For the new side pole crash tests, a crash-rating dummy representing a small-sized adult female is placed in the driver’s seat and is secured with the vehicle's seat belt. During a side pole crash test a vehicle strikes a 25 cm diameter pole at a 75 degree angle at 20 mph. The pole mimics narrow fixed objects like utility poles and trees that are often involved in side crashes. Since all rated vehicles impact the same size pole, it is possible to compare all vehicles with each other when looking at side pole crash protection ratings. .
Since there is only one dummy in the pole test, the overall pole test rating is equal to the star rating for the front seat occupant. .
d. IIHS Side Ratings
In crashes between cars and other passenger vehicles during 2000- 01, almost 60 percent of the driver deaths in the cars struck on the driver side were hit by SUVs or pickups. Due to the height incompatibility between the large size SUV-type vehicles and smaller vehicles, especially passenger cars, the occupants in the cars are much more exposed to head injury, compared with car-to-car side impacts. Often, when an SUV crashes into a passenger car, the impact point is near the occupant’s head of the passenger car.[5] . In 2003, IIHS began a side impact crash test program to specifically address this height incompatibility. They designed a moving 3300 lb. barrier to represent the front-end geometry of a typical SUV or pickup. Compared with NHTSA’s barrier, this one is higher off the ground, taller, and impacts at 31 mph perpendicular into the driver’s side of a passenger vehicle. Dummies are positioned in the driver seat and the rear seat behind the driver. There are no direct correlations available yet comparing side impact ratings with traffic fatalities. However, according to Brian O’Neill, president of IIHS, “In real world crashes of similar severity [to IIHS crash test] without side airbags, there would be a high likelihood of serious head injuries and rib fractures [for many of the vehicles tested]”.[6] . IIHS uses a qualitative rating system for side impact, similar to their offset frontal crash test rating system, consisting of 4 scores: GOOD, ACCEPTABLE, MARGINAL, and POOR. Each vehicle’s overall side impact rating is based on injury measurements, structural performance and head protection. So, unlike NHTSA’s side impact rating system, IIHS’s ratings do include head injury evaluation.
e. Head-Protecting Side Impact Airbags
IIHS side crash testing demonstrated that most vehicles tested did a poor job of protecting the dummy’s head during a side impact with an SUV-type vehicle. However, when 4 2004 vehicles rated “POOR” were re-tested, after incorporating their optional equipment, head-protecting side airbags (also referred to as curtain airbags):
For 2006 model-year, IIHS lists 18 vehicles tested for side-impact, both with and w/o side-curtain airbags. Of those 18
These results are dramatic. While head-protecting side airbags, alone, do not ensure good side impact crashworthiness, based on limited sampling, they appear to be very effective and, therefore, should be considered essential. Because of the substantial life-saving potential of these airbags a new federal regulation has been proposed.
. . Another consideration for side impact head protection awareness is that side airbags in some vehicles are actually designed only for torso protection, and not head protection. Often, but not always, the manufacturer refers to head-protecting airbags as "side-curtain" airbags. Make certain the vehicle you are considering has side airbags that extend to the head level. Also, in some vehicles that do provide side head-protecting airbags, they are only available for front seat occupants, not rear; others for driver’s side, front only. Based on your planned usage of the vehicle, you should restrict your vehicle selection considering these additional limitations. . In order to combine the side impact ratings provided by NHTSA and IIHS the SCORE assumes equal weight to each agency's ratings. Therefore, since side impacts are responsible for 26% of all U.S. traffic fatalities (i.e., 26 points out of 100), the SCORE allocates 13 points to IIHS and 13 points to NHTSA (which is further subdivided into 6.5 points for NHTSA's front seat rating and 6.5 points for NHTSA's rear sear rating). Since NHTSA's star rating system does not include the effect of head injury, the availability of side-curtain airbags is assumed not to have any effect on NHTSA's ratings in the SCORE. . For purposes of quantifying the benefit of side-curtain airbags it is assumed that their availability reduces fatality risk by 45% and that this reduction applies only to the IIHS rating and only when side impact testing has not been performed. (When IIHS side impact ratings are available the SCORE presumes that the benefits of these airbags have already been included in these ratings.) For the purpose of defining the "average" vehicle configuration, the SCORE presumes that the "average" vehicle receives only half benefit, (22.5% reduction in fatality risk) i.e., the "average" vehicle has 77.5% x the risk of vehicles rated "MARGINAL" for side impact by IIHS. * * *
(IV) Rear Impact
Although only 3% of all traffic fatalities are attributed to rear impact there are some fundamental design considerations that greatly reduce your risk of injury when you are involved in this type of collision. . Whiplash neck injury occurs after a vehicle is struck from behind and when the occupant's head lags behind the accelerated motion of the torso. Through proper seat and head restraint design it is possible to minimize the lag between the torso and head acceleration, thereby reducing the stretching of the neck. . * * (V) Rollover
a. NHTSA Ratings
With the increasing popularity of SUVs and pickups there has been a corresponding rise in deaths due to rollovers since these categories of vehicles tend to be relatively top-heavy, when compared with the typical passenger car. They ride higher off the ground and this high center-of-gravity position directly increases the tendency for rollover, either in sudden maneuvers or in wheel stubbing events, such as driving into a curb or onto soft grass at the side of the roadway, after the driver has lost control of the vehicle. Examination of rollover data reveals that compared with passenger cars, SUVs are approximately 2.8 times more likely to result in rollover; pickups approximately 2.0 times.
Rollovers per 100 Crashes[8]
. . The tip-up/no tip-up results are then used as inputs in a statistical model that estimates the vehicle’s overall risk of rollover in a single-vehicle crash (1 through 5 stars).
NHTSA Rollover Resistance Ratings Predicts Risk of Rollover Comparing the risk of rollover between vehicle classes it is noted that the SUVs and pickups, and to a lesser extent Vans, are significantly more likely to rollover than passenger cars and therefore, for vehicle classes other than passenger cars, it is essential that you actually see their rollover ratings. Note from the Chance of Rollover range in the bar graph that "worst" cars have about the same risk of rollover as the "best" pickups.
Rollover Resistance Ratings Distribution[9]
Vehicle type (class) is therefore an important characteristic when evaluating safety for a vehicle which has not been rated for rollover. Whereas the "average" passenger car has a 12% likelihood of rolling over in a single-vehicle crash, SUVs and Pickups have approximately 28% risk, and vans approximately 23% and these are the values that are assigned to this risk factor for vehicles that have not been rated for rollover. Rollovers account for 28% of all U.S. traffic fatalities and for purposes of defining the "average" vehicle 12% risk of rollover for the average passenger car is assumed to result in 33 points of risk (33 out of 100 points total). Vehicles such as SUVs and Pickups that have not been rated for rollover resistance must be assumed to have the average risk of rollover for their class of vehicle (28% which is 2.3 times greater than the 12% risk associated with the average passenger car). Therefore, the SCORE for SUVs and Pickups which have no rollover rating data available is 148 = {43 + 26 + (2.3 x 33) + 3} (vs. 100 for passenger cars). This demonstrates that, overall, these classes of vehicle are 48% more likely to result in your fatality than a passenger car, based on rollover considerations alone.
b. Electronic Stability Control (ESC)
In September 2004 NHTSA released a preliminary report which indicated that Electronic Stability Control (ESC) systems may be effective in reducing the number of single-vehicle crashes, including rollovers. The study found that the technology has proved particularly effective for SUVs.[10] . The ESC system improves the vehicle’s lateral stability and, at the same time, electronically combines the attributes of anti-lock brakes and traction control systems to help a driver avoid a potentially dangerous situation. The ESC may, therefore, avoid loss of control that otherwise could result in rollover. In 2003, only 7 percent of passenger vehicles incorporated some form of ESC however by 2006 that level was up to 55%. . Among vehicles in NHTSA’s study, ESC was associated with a 43 percent reduction in fatalities. The agency emphasized that the results are preliminary and that it will have more confidence in the effectiveness of ESC when studies can evaluate a larger cross-section of the vehicle fleet. Although these results are preliminary they are too significant to be disregarded. Therefore, The SCORE imputs the benefit of ESC equipped vehicles by reducing the rollover risk levels for vehicles equipped with ESC (i.e., 21.5% reduction in rollover risk vs. the average vehicle.) . It is also presumed that the average vehicle incorporates ESC but with only 50% effectiveness (i.e., 21.5% reduction in rollover risk.) .
. Rollovers in single vehicle crashes can be either "tripped" or "un-tripped" but the overwhelming majority (over 95%) are tripped, and NHTSA advises that ESC has little or no effect in preventing a rollover once a vehicle is committed to a tripped event. However, ESC appears to be very effective at preventing vehicles from reaching the point of being tripped since that generally requires loss of control and/or significant sideslip of the vehicle. . ESC has a relatively small direct effect on the NHTSA published rollover risk however it appears ESC has the potential to have a very large indirect effect by preventing the conditions that lead to many vehicle rollovers, i.e., by preventing single vehicle crashes. Because of its potential significant impact of reducing fatalities NHTSA plans to mandate ESC for all passenger vehicles, with full implementation by year 2012. .
c. Roof Strength
Beginning with 2010 vehicles IIHS performs a roof crush test to determine roof buckling strength. IIHS estimates that roof strength is significantly related to risk of death or serious injury in single vehicle rollover accidents. . . .
[2] http://www.nhtsa.dot.gov/NCAP/Info.html#iq1 [3] IIHS updated study published March '05. Go to http://www.iihs.org/srpdfs/sr4003.pdf [4] http://www.highwaysafety.com/news_releases/2004/pr020504.htm [5] http://www.highwaysafety.com/vehicle_ratings/ce/def_side.htm] http://www.highwaysafety.com/news_releases/2004/pr041804.htm [7] http://www.nhtsa.dot.gov/nhtsa/announce/press/pressdisplay.cfm?year=2004&filename=pr22-04.html] NHTSA General Estimates System, 1999 [9] http://www.safercar.gov/Rollover/pages/RatSysVCompare.htm [10] http://www.nhtsa.dot.gov/nhtsa/announce/press/pressdisplay.cfm?year=2004&filename=pr42-04.html] http://www-nrd.nhtsa.dot.gov/pdf/nrd-30/NCSA/TSFAnn/TSF2003EarlyEdition.pdf (chapter 2) [12] http://www.nhtsa.dot.gov/cars/rules/regrev/evaluate/pdf/809662.pdf] IIHS updated study published March '05. Go to http://www.iihs.org/srpdfs/sr4003.pdf
[1] For model year 2005 the median passenger car SCORE = 100.
[2] IIHS's 2005 status report "The Risk of Dying" http://www.iihs.org/srpdfs/sr4003.pdf.
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