From: Schwartz.Philip@epamail.epa.gov [mailto:Schwartz.Philip@epamail.epa.gov] Sent: Wednesday, March 24, 2010 11:50 AM To: Achanta, Chandana L. Subject: Fw: For OMB Submittal: Safety RIA and Preamble for GHG Vehicle

Rule

(See attached file: Section II.G -- joint safety section for CAFE-GHG preamble -- 18 Mar 10.docx)(See attach ed file: RIA Ch 07 6 Weight Reduction and Vehicle Safety 3 24 2009 toOMB.docx)

[attachment "Section II.G -- joint safety section for CAFE-GHG preamble -- 18 Mar 10.docx" deleted by Tad Wysor/AA/USEPA/US ] [attachment "RIA Ch 07 6 Weight Reduction and Vehicle Safety 3 24 2009 toOMB.docx" deleted by Tad Wysor/AA/USEPA/US]

### 7.6 Weight Reduction and Vehicle Safety

Over the past 20 years there has been a ge nerally increasing trend in the weight of vehicles (see figure III.X-1 below from EPA’s Fuel Economy Trends Report). i There have been a number of factors contributing to this incl uding: greater penetrati on of heavier trucks, introduction of SUVs, and an increasing amount of content in vehicles (including features for safety, noise reduction, added comf ort, luxury, etc). This increa sed weight has been partially enabled by the increased efficiency of vehicles, especially in engines and transmissions. The impressive improvements in efficiency during this period have not only allowed for greater weight carrying capacity (and towing), but it has also allowed for greater acceleration performance in the fleet. As the figure also show s, little of this efficiency improvement has been realized in fuel economy gains or GHG emissions reductions.

Figure 7.6.1: Weight, 0-to-60 MPH acceleration time and adjusted fuel economy for light-duty

vehicles

During this same period, due in part to in creasing numbers of Federal Motor Vehicle Safety Standards and increasingly stringent NC AP standards from NHTSA, the safety of vehicles has also undergone tremendous improvement . Vehicles are designed to better withstand both frontal and side imp acts, occupants are protected better with increased seat belt usage and air bags, and anti-lock brakes (A BS), electronic stability contro l (ESC), and improved tires and suspensions help drivers avoid accidents. NHTSA stated in its NPRM that it anticipated a 12.6 percent reduction in fatality levels between 2007 and 2020 with safety improvements due to pending NHTSA FMVSS and other factors, such as behavioral improvements (less drunk drivingand increased seat belt usage, for example). 1

, 2 Assuming that safety improvements will be made evenly throughout that period, EPA estimates the reduction in fatalities between 2007 and 2016

to be 8.7%.

The interplay between vehicle weight and poten tial impact on safety is complex. While certainly an effective option for reducing CO 2 emissions, the reduction of vehicle weight is a controversial and complicated t opic. The EPA believes that though much work has been done to advance the understanding of the effects of vehicle weight on safety, there is much yet to do. EPA also acknowledges that for the analysis of va rious topics contained in this RIA and in the preamble, there are a number of uncertainties which exist with these analysis and any results must be viewed in light of those uncertainties. In the context of safety, for example, due to limitations in modeling consumer and producer beha vioral responses to th e new standards, this analysis does not explore the net fleetwide safe ty implications of potential changes in the

distribution of vehicles in the on road fleet (e.g., changes in the va riance of size, weight, vehicle types on the road) if consumer s respond to the rulemaking by purchasing a distribution of vehicles which are significantly diffe rent than what EPA has forecast.

This section of the RIA describes and compares some of the key studi es that have been conducted in the recent past – including NHTSA’s recent 2010 analysis, and presents some potential research options going forward.



### 7.6.1 What did EPA say in the NPRM and in the Draft RIA with regard to potential safety effects?

In the NPRM, EPA discussed potential safety e ffects of the proposed standards. In the joint technology analys is, EPA and NHTSA predicted that automakers could reduce vehicle weight as one part of the industry’s strategy for meeting the proposed standards. EPA’s modeling projected (and still proj ects) that vehicle manufacturers will reduce the weight of their vehicles by 4% on average between 2011 and 2016, w ith the average per-vehicle mass reduction in absolute terms being greater for light-trucks than for passenger cars. For the NPRM, this mass reduction estimate was generally smaller on both an absolute and a percenta ge basis for smaller car than for larger vehicles. Specifically, we es timated an average reduction of 2.3% (62 lbs) for

1 NHTSA stated in section IX of their PRIA for this rule: “The agency examined the im pacts of identifiable safety trends over the lifetime of the vehicles produced in each mode l year. An estimate of these impacts was contained in a previous agency report. (The next citation in this document, Blincoe, L. and Shankar, U, January 2007.) The impacts were estimated on a year-by-year basis, but could be examined in a combined fa shion. The agency assumed that the safety trends will result in a reduction in the target population of fatalities from which the weight impacts are derived. Using this method, we found a 12.6 percen t reduction in fatality levels between 2007 and 2020. The estimates derived from applying Kahane ’s percentages to a baseline of 2007 fatalities were thus multiplied by 0.874 to account for changes th at the agency believes will take place in passe nger car and light truck safety between the

2007 baseline on-road fleet used for th is particular analysis and year 2020.

2 Blincoe, L. and Shankar, U, “The Impact of Safety Standards and Behavioral Trends on Motor Vehicle Fatality Rates,” DOT HS 810 777, January 2007. See Table 4 comparing 2020 to 2007 (37,906/43,363 = 12.6% reduction.cars with a curb weight below 2,950 lbs, 4.4% (154 lbs) for cars with a curb weight above 2,950, 3.5% (119 lbs) for trucks with a curb weight below 3,850 lbs, and 4.5% for trucks with a curb weight above 3,850 lbs (215 lbs). The penetration and magnitude of these modeled changes are consistent with the public announcements made by many manufacturers si nce early 2008 and are consistent with meetings that EPA has had with senior engineers and t echnical leadership at many of the automotive companies during 2008 and 2009.

Between September 2008 and March 2009, EPA met with 11 major auto companies: GM, Chrysler, Ford, Nissan, Honda, Toyota, Mits ubishi, Hyundai/Kia, BMW, Mercedes and Volkswagen. Each company announced plans to reduce vehicle weight broadly across the passenger car vehicle and light tr uck categories within the 2012 to 2016 timeframe. Their plans for vehicle weight reduction are not limited to a single weight class but instead are expected to be implemented widely across their products. Th e following statements summarize a number of automotive manufacturers’ future plans to reduce vehicle weight announced in the public domain within the past two year: 3

• Ford: 250 to 750 pound weight reductions 2012 to 2020 across all vehicle platforms

• Toyota: 30% weight reduction on 2015 Corolla and a 10% weight reduction on mid-size vehicles by 2015

• Nissan: 15% average weight reduction by 2015

• Mazda: 100 kg (220 pound) weight reduction by 2011 and an additional 100 kg weight reduction by 2016

• Mercedes: 5% average we ight reduction by 2015

The EPA believes that reducing vehicle mass of th e magnitude we estimated for the proposal and the final rule (up to 10% for certain vehicles by model year 2016)without reducing the size, footprint or the structural integrity of the vehicl e is technically feasible . Many of the technical options for doing so are outlined in Chapter 3 of the joint TSD and in this RIA. In the NPRM, EPA described how weight reduction can be accomplished by the proven methods described below. Every manufacturer can employ these me thodologies to some degree, the magnitude to which each will be used will depend on opportun ities within individual vehicle design.

• Material Substitution : Substitution of lower density and/or higher strength materials in a

manner that preserves or improves the func tion of the component. This includes substitution of high-strength steels, alumin um, magnesium or composite materials for components currently fabricated from m ild steel, e.g., the magnesium-alloy front structure used on the 2009 Ford F150 pickups (we note that since these MY 2009 F150s have only begun to enter the fleet, there is little real-world cras h data available to evaluate the safety impacts of this new de sign). Light-weight materials with acceptable energy absorption properties can maintain stru ctural integrity and absorption of crash energy relative to previous designs while pr oviding a net decrease in component weight. In their comments to the proposed rule, the American Iron and Steel Institute (AISI)

noted: “AISI has shown in its research with the Auto/Steel Partnership and in programs

3 Insert reference or footnote.supported by the U.S. Department of Ener gy, the use of new Advanced High Strength Steel (AHSS) steel grades can enable the mass of critical crash structures, such as front rails and bumper systems, to be reduced by 25%.”

• Smart Design : Computer aided engineering (CAE) tools can be used to better optimize

load paths within structures by reducing st resses and bending mome nts without adversely affecting structural integrity. This allows better optimization of the sectional thicknesses of structural components to reduce mass while maintaining or improving the function of the component. Smart designs also integrate separate parts in a manner that reduces mass by combining functions or the reduced use of separate fasteners. In addition, some “body on frame” vehicles are redesigned with a li ghter “unibody” constr uction with little compromise in vehicle functionality.

• Reduced Powertrain Requirements : Reducing vehicle weight su fficiently allows for the

use of a smaller, lighter and more effici ent engine while maintaining or increasing performance. Approximately half of the ma ss reduction that can be realized in the powertrain is due to reduced powertrain output requirements. The subsequent reduced rotating mass (e.g. transmission, driveshafts/ha lfshafts, wheels and tires) via weight and/or size reduction of components are made possible by reduced torque output requirements.

• Mass Decompounding : Following from the point above, the compounded weight

reductions of the body, engine and drivetra in can reduce stresses on the suspension components, steering components, brakes, and th us allow further reduc tions in the weight of these subsystems. The reductions in weight for unsprung masses such as brakes, control arms, wheels and tires can further reduce stresses in the suspension mounting points which can allow still further reductions in weight. For example, mass reduction

can allow for the reduction in the size of th e vehicle brake system, while maintaining the same stopping distance. It is estimated that 1.25 kilograms of secondary weight savings can be achieved for every kilogram of weight saved on a vehicle when all subsystems are redesigned to take into account the initial primary weight savings. ii

The EPA stated in the NPRM that it believes that weight reduction is broadly applicable across all vehicle subsystems including the engine, exhaust system, transmission, chassis, suspension, brakes, body, closure panels, glazing, s eats and other interior components, engine cooling systems and HVAC systems. EPA menti oned that it is both technically feasible to reduce weight without reducing vehi cle size, footprint or structur al strength and manufacturers have indicated to the agencies th at they will use these approaches to accomplish these goals. We requested written comment on this assessment a nd this projection, incl uding up-to-date plans regarding the extent of use by each manufacturer of each of the methodologies described above.

EPA also projected that automakers will not reduce vehicle footprint in response to the proposed CO2 standards in our modeling analysis . NHTSA and EPA have taken two measures to help ensure that this fi nal rule does not provide an in centive for mass reduction to be accompanied by a corresponding decrease in the foot print of the vehicle (with its concomitant decrease in crush and crumple zones). The first design feature of the pro posed rule is that the

CO 2 or fuel economy targets are based on the attri bute of footprint (which is a surrogate forvehicle size). 4 The second design feature is that the shape of the footprint curve (or function) has been carefully designed with the intention that it neither encour ages manufacturers to increase, nor decrease the footprin t of their fleet. Thus, the standard curves are designed to be approximately “footprint neutral” with in the sloped portion of the function. 5 For further discussion on this, refer to Section II.C of the pream ble, or Chapter 2 of the joint TSD. Thus the agencies assumed in their modeling analysis th at the manufacturers could reduce vehicle mass without reducing vehicle footprint as one way to respond to the standards. 6 However, EPA acknowledges some uncertainty re garding how consumer purchases will change in response to the vehicles designed to meet the model year s 2012-2016 standards. This could potentially

affect the mix of vehicles sole in the future , including the mass and f ootprint distribution, and thus result in a different impact on safety than is discussed and presente d in this final rule.

EPA also discussed safety in the context of NHTSA’s analysis presen ted in Section IV of the NPRM preamble, in which NHTSA presented an analysis of the prop osed CAFE standards based on the 2003 Kahane safety analysis. NHT SA’s Dr. Charles Kaha ne performed a thorough review on historical data rega rding the relationship between mass reduction, wheel base, track width and fatality risk. iii

, iv The results from 1991-1999 vehicl e data indicate that a heavier vehicle is safer than a lighter one based on the as sumption that historical vehicle mass reductions are accompanied with vehicle si ze and footprint reductions. Based on this, NHTSA developed and presented a worst case estimate of the e ffect of weight reductions on fatalities. The underlying data used for that analysis did not allow NHTSA to analyze the specific effect of weight reduction at constant footprint because hist orically there have not been a large number of vehicles produced that relied s ubstantially on material substituti on. Rather, the data set included

vehicles that were either smalle r and lighter or larger and heav ier. The numbers in the NHTSA analysis predicted the safety-related fatality cons equences that would occu r in the unlikely event that weight reduction for model years 2012-2016 is accomplished by reducing mass and reducing footprint (as well as structural integrity). EPA acknowledged that the safety analysis conducted by NHTSA and presented in Section IV of the NPRM Preambl e could be a worst case analysis for fatalities, but that the actual effects on vehicle safety could (a nd would likely) be much less. However, EPA and NHTSA were not able to qu antify the lower-bound potential effects at that

time.

Thus, the 2003 and earlier Kahane studies (as summarized in the NPRM) concerning weight reductions and safety indi cate that there is not a clear cu t answer to the issue before the agencies of potential safety impacts of the ru le due to mass reduction which may occur in the

fleet absent size reductions. These studies draw upon histor ical vehicle data where mass reduction were (for the most pa rt) linked with size reductions, t hus they occurred in ways different from the way the agencies proj ect weight reduction w ill occur for MY 2012-2016 vehicles. As such the pre-2010 Kahane studies ma y not be directly rele vant to predicting or quantifying the safety impact of th e projected use of weight reducti on technologies in this rule.

4 As the footprint attribute is defined as wheelbase times track width, the footprint target curves do not discourage manufacturers from reducing vehicle size by reducing front, rear, or side overhang, which can impact safety by resulting in less crush space. However, EPA does ackn owledge that front and rear and side overhang are not included in footprint and that there may be changes in this part of the vehicle in the future.

5 This neutrality with respect to foot print does not extend to the smallest a nd largest vehicles, because the function is limited, or flattened, in these footprint ranges

6 See Chapter 1 of the joint TSD for a description of po tential footprint changes in the 2016 reference fleetSeveral commenters to the proposed rule support this conclusion, includ ing the International Council on Clean Transportation (I CCT): “The results of the Kahane study would be great for analyzing the safety impacts of a weight-bas ed attribute system.... Kahane’s methodology was simply not designed to assess the safety impact s of lightweight materi als.”, and the National Association of Clean Air Agencies (NACAA): “si gnificant portions of NHTSA’s safety analysis

are based on out-of-date data”.

In contrast to the pre-2010 Kahane studies, Dynamic Resear ch Incorporated (DRI) has assessed the independent effects of vehicle weight and size on safe ty in order to determine if there are tradeoffs between impr oving vehicle safety and fuel c onsumption In their 2005 studies,

v
, vi

, 7 DRI presented results that indicated that vehicle weight reducti on tended to decrease fatalities, but vehicle wheelbase and track reduction tended to increase fatalities.

In the RIA for the proposed rule, EPA attempted to summarize DRI’s results in four major points. These points are re-summarized belo w to reflect comments from DRI as to present this information more accurately: 8

1. 2-Door vehicles represented a significant po rtion of the light duty fleet and should not be ignored.

2. Directional control and therefore crash a voidance improves with a reduction in curb weight and/or increases in wheel base and track.

3. The occupants of the impacted vehicle, or “collision partner” benefit from being impacted by a lighter vehicle.

4. Rollover fatalities are reduced by a reducti on in curb weight due to a potentially lower center of gravity and lower loads on the roof structures.

The data used for the DRI analysis was si milar to that used in NHTSA’s 2003 Kahane study, using Fatality Analysis Reporting System (FARS) data for vehicle model years 1985 through 1998 for cars, and 1985 through 1997 trucks. This data overlaps Kahane’s FARS data on model year 1991 to 1998 vehicles. DRI also us ed a logistic regression method similar to the approach taken by the 2003 Kahane study. Ho wever, DRI included 2-door passenger cars, whereas the Kahane study excluded all 2-doo r vehicles. The 2003 Kahane study excluded 2- door passenger cars because it found that for MY 1991-1999 vehicles; sports and muscle cars constituted a significant proportion of those vehicles. NHTSA stat ed that these vehicles have relatively high weight relative to their wheelbase , and are also disproportionately involved in crashes. Thus, Kahane conclude d that including these vehicles in the analysis excessively skewed the regression results. As of July 1, 1999, 2-door passenger cars represented 29% of the

7 One of these studies was published as a Society of Automotive Engineers Technica l Paper and received peer review through that body

8 DRI stated: “The DRI work focused on the effects of vehicle size and weig ht (i.e. curb weig ht, wheelbase, and track) on vehicle crash avoidance, cras hworthiness, and compatibility, based on accident and fatality data. There were numerous conclusions in addition to those listed, including the benefits of both increased size and weight.”registered cars in the United States. 9 The majority of 2-door vehicles excluded in the 2003 Kahane study and included in DRI's analysis were high-sales volume light-duty vehicles and vehicles shared common vehicle platforms and architectures with 4-door vehicles that were included in the 2003 Kahane study. DRI’s position was that this is a significant portion of the light duty fleet, too large to be ignored, and conclusions regard ing the effects of weight and safety should be based on data fo r all cars, not just 4-doors.

DRI did, however, state in their conclusions that the results are sensitive to removing data for 2-doors and wagons, and that the results for 4-door cars with respect to the effects of wheelbase and track width were no longer statistically significant when 2-door cars were removed. EPA and NHTSA (along with many comm enters) recognized the technical challenges of properly accounting for 2-door car s in a regression analysis eval uating the impacts of vehicle weight on safety, due to the concerns di scussed in the 2003 Kahane study above.

The DRI and Kahane studies also differed with respect to the impact of vehicle weight on rollover fatalities. The Kahane study treated curb weight as a surrogate for size and weight and analyzed them as a single variable. Using this method, the 2003 Kahane analysis indicated that curb weight reductions would in crease fatalities due to rollovers. The DRI study differed by analyzing curb weight, wheelbase, and track as multiple variables and concluded that curb weight reduction would decrease rollover fatalities, and wheel base and track reduction would

increase rollover fatalities. DRI offered two potential root causes for higher curb weight resulting in higher rollover fatalities . The first is that a taller ve hicle tends to be heavier than a shorter vehicle; therefor e heavier vehicles may be more lik ely to rollover because the vehicle height and weight are correlated with vehicle ce nter of gravity height. The second is that FMVSS 216 for roof crush strength requirements for passenger cars of model years 1995 through 1999 were proportional to the unloa ded vehicle weight if the we ight is less than 3,333 lbs, however they were a constant if the weight is greater than 3,333 lbs. Therefore heavier vehicles may have had relatively less rollover crashworthiness.

In the NPRM, NHTSA rejected many elements of the DRI analysis, and did not rely on it for its evaluation of safety impact changes fr om the proposed CAFE standards. See Section IV.G.6 of the Notice of Proposed Rulemaking, as well as NHTSA March 2009 Final Rulemaking for MY2011 CAFE standards (74 FR at 14402-05).

The DRI analysis concluded that there would be small additi onal reductions in fatalities for cars and trucks if the weight reduction occurs without accomp anying vehicle footprint or size changes. EPA noted that if DRI’s results were to be applied using the curb weight reductions predicted by the OMEGA model, an overall reduc tion in fatalities would be predicted. There were many commenters who supported this notio n. Further discussion of these comments is

included below.

9 Specific examples include the Chevrolet Cavalier and Monte Carlo, Oldsmobile Achieva and Supreme, Buick Riviera, Ford Escort and Probe, Me rcury Tracer, Honda Civic, Hyundai A ccent, and VW Golf which do not necessarily represent high-weight, short-wheelbase sports and high -performance vehicle types.

### 7.6.2 What public comments did EPA receive in regard to its safety discussion and what is EPA’s response?

EPA requested and received public comments from several sources regarding the NPRM Preamble positions noted above. Many of the co mments received were in support of EPA’s safety assessment, such as those from Dynamics Research Institute (DRI), International Council on Clean Transportation (ICCT), Public Citizen, Un ion of Concerned Scientists, California Air Resources Board (CA-ARB) and the National Asso ciation of Clean Air Agencies (NACAA).

In a technical comment, DRI’s agreed with EPA that directional control and therefore crash avoidance improves with a reduction in cu rb weight. DRI went further and commented that control also improved with an increase in wheel base and track width., The latter point acknowledges that a corresponding potential decreas e in wheel base or track width could result

in an increase in fatalities. DRI offered result s from the application of the “quasi-steady vehicle directional equations of moti on”. These results show “tha t passenger cars with shorter wheelbases tend to have smaller characteristic sp eeds, resulting in highe r [yaw rate] natural frequency and less damping, based on analysis of quasi-steady vehi cle equations of motion”.

EPA concurs with DRI’s comments regarding their analysis. This supports the argument made by EPA in the NPRM that, vehicles with reduced mass are better able to avoid accidents

that cause fatalities due to increased vehicle maneuverability that better matches a driver’s intended steering inputs. 10 EPA analyzed Consumer Reports Double Lane Change Data 11 to determine how curb weight affects emergency ha ndling. Consumer Reports provided EPA with a summary of their double lane change tests for vehicles from MY 2003 through MY 2010 along with the vehicles’ curb weight. 12 By plotting the vehicle double lane change speed with respect to curb weight, EPA is able to show how the sp eed at which a double lane change can be safely executed goes up as curb weight decreases, as sh own in Figure 7.6.2 below. As the weight of all vehicles is decreased, their maneuverability and handling will increase, thus giving the driver greater control and increased capability to avoid accidents. This relationship held true for both vehicles equipped with and wit hout Electronic Stability Control (ESC), although the same data show that capability is further enhanced with the addition of ESC. At any given curb weight, the addition of ESC resulted in a higher average dou ble lane change speed than those vehicles without stability control. Unde r all stability control events, the ESC system will be working against the momentum of the vehicle. Reductions in mass will generally increase ESC effectiveness in terms of the ability of a vehicl e to enter a double lane change maneuver at a higher speed. However, NHTSA’s review of historical FARS data for MY 1991-1999 cars has found that smaller cars are responsible for a higher number of crashes than other vehicle types.

10 FMVSS126 - “Oversteering and underst eering are typically cases of loss-of-c ontrol where vehicles move in a

direction different from the driver’s intended direction ”.

11 The Consumer Reports double lane change maneuver is referred to as “Emergency Handling” within Consumer Reports vehicle assessments. The maneuver consists of a set of traffic cones arranged in such a pattern as to force the vehicle into a left lane, and then a return to the right lane over a controlled distance. The double lane change speed is based on the driver’s entrance speed at the beginn ing of the course. The high est entrance spee d with which the driver is able to negotiate the c ourse without disturbing the cones is deemed the “Emergency Handling” metric.

12 The data used for Figure 7.6.2 is available in the memorandum “Vehicle Double Lane Change Data Provided by Consumer Reports”, which has been placed in the EPA docket for this final rule.Vehicles equipped with ESC: y = -0.0026x + 62.114

R 2 = 0.5282

Vehicles without ESC y = -0.0025x + 59.921

R 2 = 0.4085

40 45 50 55 60 65

1000 2000 3000 4000 5000 6000 7000

Vehicle Curb Weight (lbs)Double Lane Change Speed (MPH)

Non-ESC

ESC Vehicles

Linear (ESC Vehicles)

Linear (Non-ESC)

Figure 7.6.2: Double Lane Change Speed vs. Vehicle Curb Weight

The International Council on Clean Transpor tation (ICCT) endorsed the DRI comments (described in the previous secti on) in their comments to the propos al. ICCT went a step further and applied the DRI results to calculate a potential benefit fr om reducing curb weight while maintaining footprint. Accounting for the downw ard trend in annual vehi cle fatalities, and the actual weight reduction anticipated by agencies’ modeling results, ICCT determined that there

would be a reduction of 599 fatalities and 354 fatal ities for a 100 lb weight reduction in cars and trucks respectively.

In contrast, there were comments received from the American Ir on and Steel Institute (AISI) and the Competitive Enterp rise Institute (CEI) that cont ended EPA’s conclusions. Both

AISI and CEI noted in their comments that hist orically heavier vehicles have demonstrated a safety advantage over lighter vehicles. AISI presented the results from Desapriya that “ sedans are two times more likely to be injured than dr ivers or passengers in larger pickup trucks and

SUV’s ”, and CEI endorsed the results from the 2003 Kahane study in support of their position.

AISI also noted that: “ AISI has shown in its research with the Auto/Steel Partnership and in programs supported by the U.S. Department of Energy, the use of new (Advanced High Stength Steel) AHSS steel grades can enable mass of critical crash structures, such as front rails and bumper systems, to be reduced by 25 percent. Such vehicle structures with reduced mass can perform as well as their heavier counterpar ts in standard NHTSA frontal or IIHS offset

instrumented crash tests .” This is exactly the type of materi al substitution that EPA noted in theNPRM. In this case a vehicle can be made light er without a concomitant decrease in crush and crumple zones.

CEI noted the historical studies that analy zed the relationships between CAFE standards and vehicle fatalities, specificall y, R.W. Crandall and J.D. Graham, authors of “The Effect of Fuel Economy Standards on Automobile Safety” and the 2003 Kahane report. According to CEI, the Crandall and Graham analysis reported that CAFE regulations had a downsizing effect of 500 pounds per car in 1989. Th e applicability of the 1989 anal yses is questionable in the

context of this rule and its associated eff ectiveness from MY 2012 through 2016. Vehicle design capability, including computer ai ded engineering (CAE) has changed substantially in the 20 years since this report was completed. Increase d stringency of FMVSS st andards combined with the improved strength of materi als available and used in auto mobile manufacturing has allowed auto manufacturers to improve impact performance without a co mmensurate increase in vehicle weight. In addition, the 500 pound reduction analyzed by Crandall and Graham is substantially greater than the estimated weight reduction associated with this final rule. Regarding the 2003 Kahane report, NHTSA has rec ognized some of the limitation s of the 2003 analysis in the context of this rulemaking and presents a summ ary and review of the 2010 Kahane report in the preamble and within NHTSA’s FRIA.

CEI further comments that “new technologies and attribute-based regulation will not eliminate the safety tradeoff”. CEI states that “ some proponents of higher CAFE standards, and of CO2 emission limits, claim that new technologies can eliminate th ese lethal effects. This claim is simply false, even if such technologies do notthemselves involve downsizing. Consider a hitech prototype car capable of meeting eith er a higher CAFE standard, or a stringent CO2 emissions standard. Imagine that you then increase this car’s size and weight by adding several cubic feet of trunk space and occupant space. The result would be an even safer car. ” EPA recognizes that more recent vehicles have more safety features than 1990s vehicles, which are likely to make them safer overall. To account for this, NHTSA did adjust the results of both its NPRM and final rule analysis to include known safety improvements, like ESC and increases in seat belt use, that have occurred since MYs 1991-1999. 13 However, simply because newer vehicles have more safety countermeasures, doe s not mean that the we ight/safety relationship necessarily changes. More like ly, it would change the target popul ation (the number of fatalities) to which one would apply the weight/safety relationship. Th us, EPA acknowledges that while mass reduction can be done in a safety neutral manner, some mass reduction techniques for both passenger cars and light trucks can make them less safe in certain crashes as discussed in

NHTSA’s FRIA. 14

13 See Chapter IX of the NHTSA FRIA for details on this adjustment.

14 If one has a vehicle (vehicle A), and both reduces the vehicle’s mass and adds new safety equipment to it, thus creating a variant (vehicle A 1 ), the variant might conceivably have a level of overall safety for its occupants is equal to that of the original vehicle (vehicle A). However, vehicle A 1 might not be as safe as second variant (vehicle A 2 ) of vehicle A, one that is produced by adding to vehicle A the same new safety equipment added to the first variant, but this time without any mass reduction.Additional comments received from the AISI challenge the agencies’ conclusions with regard to vehicle size. While they agree that “the historical relations hip between vehicle size, weight, and collision severity may be influen ced by design and structural improvements”, they assert that “the aggressive schedule for implem enting the proposed rule assures that carmakers will be manufacturing smaller, lighter vehicles in order to comply.” Porsche and IIHS had similar comments implying that footprint standards will increase the risk that manufacturers will make vehicles smaller. In response, EPA does not feel that the schedule is overly aggressive. The standards and their phase-in period is feasib le and economically prac tical as described in section III.D of the preamble. That same disc ussion, as well as the supporting analysis in the joint TSD, demonstrates a clear compliance pa th to meeting the st andards based on wider penetration of existing technologies , at reasonable and affordable co st. In addition, the attributebased approach, along with the shape of footprint curve has been developed with the objective of minimizing the incentive to downsize (since, am ong other things, downsizing simply creates a more stringent regulatory target corresponding to the downsized footprint) nor to upsize (as that could incur significant redesign costs and also would likely increase the mass of the vehicle which could off-set any benefit in upsizing fr om a stringency perspective as a higher mass vehicle will produce more CO2 emissions). EPA consequently does not accept the commenter’s assertion. However, as discussed in Sections III.H.1 and IV.G.6 of the preamble, the agencies acknowledge some uncertainty regarding how consumer purchases will change in response to the vehicles designed to meet the MYs 2012-2016 standard s. This could potentially affect the mix of vehicles sold in the future, includ ing the mass and footpr int distribution.



### 7.6.3 NHTSA’s 2010 Study of Accident Fatalities by Vehicle Size and Weight

In response to comments received and in an effort to follow through on some of its NRPM pledges for consideration in the future , NHTSA has significantl y revised its 2003 study on the relationship between vehicle mass and fatalities in the context of this 2012-2016 rulemaking. A copy of this new report, “Rela tionships Between Fatality Risk, Mass, and Footprint in Model Year 1991- 1999 and Other Passenger Cars a nd LTVs”, Charles J. Kahane, NCSA, NHTSA, March 2010, has been placed in the docket for this rulemaking, hereafter referred to as the 2010 Kahane report. 15 In the new 2010 Kahane report, based on the original MY 1991-1999 vehicle data set, NHTSA addresses several criticisms, sp ecifically including 2- door vehicles in its passenger car analysis, atte mpting to separate weight and footprint as independent variables and their a ssociated contributions to vehicl e fatalities, and comparing their

results to those from DRI. We note that this analysis looks speci fically at impacts on fatalities. EPA and NHTSA have not analyzed the impact of mass reduction predicted from this final rule

on non-fatal accidents. We also not e that the results of the 2010 Ka hane analysis, as applied to the mass reductions predicted from this rulemaking, must be viewed in th e overall context of our projection of the 2012-2016 new vehicl e fleet distribution (See Chap ter 1 of the Joint TSD for a

discussion of how EPA a nd NHTSA have developed the project ed future new vehicle fleet).

15 NHTSA intends for this 2010 Ka hane report to undergo a peer review in accordance with OMB guidance for peer review, and the results of this peer review and any subsequent revisions to the report will be made available to the public upon completion.EPA acknowledges some uncertainty regarding how consumer purchases may change in response to the vehicles designed to meet the MYs 2012-2016 standards. This could potentially

affect the mix of vehicles sold in this time frame, including th e mass and footprint distribution – which would impact the projection of fatalities fro m the 2010 Kahane analysis as applied to this

final rule.

The 2010 Kahane report presents three sets of results each with an estimate of fatalities based on the weight reductions proj ected in the feasibility analysis for the final ru le. Each of these results presents a significant departure from th e NPRM. The first set of results is a straight regression of result for passenger cars and LTVs. The passenger car data now includes 2-door vehicles, although a decision was made to continue to exclude muscle cars. The second and third sets of results, termed “uppe r bound scenario” and “l ower bound scenario” respectively, are the result of expert opinion and judgment by NHT SA as to how mass may be reduced and the potential effects, both primary for the driver and occupants of a vehicle, and secondary or societal effects. NHTSA was able to perform th ese analyses with both mass and footprint treated as independent variables in the 2010 study. The unmodified straight regression results now reflect an expected reduction of 301 fatalities for the life of MY 2012-2016 vehicles, down from

the absolute worst-case 493 in the CAFE NP RM. The new “upper bound scenario” estimates

that there will be 22 additional fatalities as the result of the CAFE rule, and the “lower bound scenario” an 80 fatality decrease 16 . These results are consistent with EPA’s NPRM claim that

fatalities as a result of the rule could be close to zero. Howe ver, NHTSA states in the new 2010 Kahane analysis that the potential fatality increases associated with mass reduction in the passenger cars would be to a larg e extent offset by the benefits of mass reduction in the heavier LTVs. As was stated in the NPRM, EPA continue s to believe that weight can be reduced from passenger cars safely through smar t design, and other methods which can be used in the model years 2012 to 2016 time frame. This is based on a number of studies in th e literature including those from DRI, Wenzel, Ross and Robertson refere nced above and elsewhere in this final rule.

Furthermore, in an effort to address public comments that promoted the DRI results as a legitimate alternative to NHT SA’s analysis, the 2010 Kahane report presents several conclusions. NHTSA first focused on the issue of “near multicollinearity” of the data. This

statistical characteristic can result in increas ed uncertainty of regres sion coefficients, which according to sources cited by NHTSA, can result in the “wrong sign or implausible magnitude”.

There are statistical tests that can be run on data used in regression models to determine the level of multicollinearity between independent variable s. NHTSA performed tests on their data set and determined that mass and footprint did exhibit “near multicollinearity”. Subsequently, NHTSA applied a 2-step regression, in accordance with DRI’s methodology, to its own data and

the results showed a corres ponding decrease in fatalities for a 100 pound mass reduction. NHTSA did not accept these results for many reasons, as outlined in the 2010 Kahane report, however their underlying conclusion was that the 2-step regression a pplied by DRI exacerbated the effects of “near multicollinearity”.

16 The “upper-estimate scenario” and “low er-estimate scenario” are based on NH TSA’s judgment as a vehicle safety agency, and are not meant to co nvey a sense of confidence in the precision of the results, but more to convey a sense of bounding for potential safety effects.The EPA has found one additional peer-revie wed study of historical FARS data.

Robertson 2006 vii analyzed somewhat newer model year passenger cars and light-trucks (1999- 2002) and used a logistic regression approach similar to the 2003 Kahane and 2005 DRI studies, including consideration of driver gender and age. The study found multicollinearity to be a problem for regressions, includi ng vehicle curb-weight and wheel base, but found turning radius

could be substituted as an indicator of ve hicle size without introducing significant multicollinearity into the regression analysis. Robertson’s analysis tested the hypothesis of reducing vehicle curb-weight to the mini mum achievable by the 1999-2002 model year population vs. vehicle size. The regression results showed a societal benefit of a 28% reduction

in fatalities for minimization of mass. Mass minimization vs a vehicle size metric is not the same as removing a fixed percent or fixed quantity of vehicle mass and thus the results are not directly comparable to either the 2010 Kahane or 2005 DRI results, but they are directionally consistent with both studies. The analysis showed similar trends to the 2010 Kahane report with increased risk of fatality to drivers of lighter vehicles, which was more than offset by the reduction in risk of fatality to ot her drivers, similar to Kahane’s 2010 results with respect to light

trucks and to DRI’s results for both light-trucks and passenger cars.

The EPA believe that while NHTSA’s new 2010 analysis significantly adds to the literature and understanding of th e effects of mass reduction on safe ty, that there still are many opportunities for further study.



### 7.6.4 Suggested Next Steps To Increase Ou r Understanding of the Effects of Vehicle Size and Weight on Fatalities

NHTSA and EPA believe that it is important for the agencies to conduct further study

and research into the interacti on of mass, size and safety to assist future rulemakings. The agencies intend to begin working collaborativel y and to explore with DOE, CARB, and perhaps other stakeholders an interagenc y/ intergovernmental working gr oup to evaluate all aspects of mass, size and safety. It would also be the goal of this team to coordinate government supported studies and independent researc h, to the extent possible, to help ensure the work is complementary to previous and ongoing research a nd to guide further research in this area. DOE’s EERE office has long funded extensive re search into component advanced vehicle

materials and vehicle mass reduction. Other agencies may have additional expertise that will be helpful in establishing a coordina ted work plan. The agencies ar e interested in looking at the weight-safety relationship in a more holistic (com plete vehicle) way, and thanks to this CAFE rulemaking NHTSA has begun to bring together parts of the agency— crashworthiness, and crash avoidance rulemaking offices and the agency’s Research & Development office—in an interdisciplinary way to better leverage the expertis e of the agency. Extendi ng this effort to other agencies will help to ensure that all aspects of the weight-safety rela tionship are considered completely and carefully with our future research. The agencies also intend to carefully consider comments received in response to the NPRM in de veloping plans for future studies and research and to solicit input from stakeholders.

The agencies also plan to watch for safety effects as the U.S. light-duty vehicle fleet evolves in response both to the CAFE/GHG standard s and to consumer preferences over the nextseveral years. Additionally, as new and advanc ed materials and component smart designs are developed and commercialized, and as manufacturers implement them in more vehicles, it will be useful for the agencies to learn more about them and to try to track thes e vehicles in the fleet to understand the relationship between vehicle de sign and injury/fatality data. Specifically, the agencies intend to follow up with study and research of the following:

First, NHTSA is in the process of contracti ng with an independent institution to review

the statistical methods that NHTSA and DRI have us ed to analyze historical data related to mass, size and safety, and to provide recommendati on on whether the existing methods or other

methods should be used for future statistical analysis of historical data. This study will include an consideration of potential multicollinearity in the historical data and how best to address it in a regression analysis. This study is being initi ated because, in response to the NPRM, NHTSA

received a number of comments related to the methodology NHTSA used for the NPRM to determine the relationship between mass and safety, as discussed in detail above.

Second, NHTSA and EPA, in consultation w ith DOE, intend to begin updating the MYs 1991-1999 database on which the safety analyses in the NPRM and final rule are based with

newer vehicle data in the next several months. Th is task will take at least a year to complete. This study is being initiat ed in response to the NPRM comments related to the use of data from MYs 1991-1999 in the NHTSA analysis, as discu ssed in the section II.G of the preamble.

Third, in order to assess if the design of r ecent model year vehicles that incorporate

various mass reduction methods affect the relati onships among vehicle mass, size and safety,

NHTSA and EPA intend to conduct collaborative statistical analysis, beginning in the next several months. The agencies intend to work with DOE to identify ve hicles that are using material substitution and smart design. After these vehicles are identified, the agencies intend to

assess if there are sufficient data for statistical analysis. If there are sufficient data, statistical analysis would be conducted to compare the relationship among ma ss, size and safety of these smart design vehicles to vehicles of similar size and ma ss with more traditional designs. This study is being initiated because, in response to the NPRM, NHTSA received comments related to

the use of data from MYs 1991-1999 in the NHTSA analysis that did not include new designs that might change the relationship among mass, si ze and safety, as discus sed in detail above.

NHTSA may initiate a two-year study of the safety of the fl eet through an analysis of the

trends in structural stiffness a nd whether any trends identified im pact occupant injury response in crashes. Vehicle manufacturers may employ sti ffer light weight materials to limit occupant compartment intrusion while controlling for ma ss that may expose the occupants to higher accelerations resulting in a greate r chance of injury in real-world crashes. This study would provide information that would increase the und erstanding of the effects on safety of newer vehicle designs.

In addition, EPA and NHTSA, possibly in collaboration with DOE, may conduct a longer-term computer modeling-ba sed design and analysis study to help determine the maximum potential for mass reduction in the MYs 2017-2021 timeframe, through direct material substitution and smart design while meeting safety regulations and guideli nes, and maintaining vehicle size and functionality. This study may build upon prior research completed on vehicle mass reduction. This study would further explore the comprehensiv e vehicle effects, includingdissimilar material joining tec hnologies, manufacturer feasibi lity of both supplier and OEM, tooling costs, and crash simulation and perhaps eventual crash testing.

i “Light-Duty Automotive Technology and Fuel Economy Trends: 1975 Through 2008”, EPA420-R-08-015, U.S. Environmental Protection Agency Office of Transportation and Air Quality, September 2008

ii “Future Generation Passenger Compartment-Valid ation” in “Lightweig hting Materials – FY 2008 Progress Report”, U.S. Department of Ener gy, Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Program, May 2009.

iii “Relationship between Vehicle Size and Fatal ity Risk in Model Year 1985-93 Passenger cars and Light Trucks”, DOT HS 808 570, NHTSA Technical Report, January 1997

iv “Vehicle Weight, Fatality Risk and Crash Compatibility of Model Year 1991-99 Passenger Cars and Light Trucks”, DOT HS 809 663, NHTSA Technical Report, October 2003

v “Supplemental Results on the Independent Effect s of Curb Weight, Wheelbase and Track on Fatality Risk”, Dynamic Research, Inc., DRI-TR-05-01, May 2005

vi “An Assessment of the Effects of Vehicle Weight and Size on Fatality Risk in 1985 to 1998 Model Year Passenger Cars and 1985 to 1997 Mode l Year Light Trucks and Vans”, Van Auken, M., Zellner J.W., SAE Technical Paper Number 2005-01-1354, 2005.

vii “Blood and Oil: Vehicle Character istics in Relation to Fatality Ri sk and Fuel Economy”, L.S. Robertson, American Journal of Public Health, Vol. 96, No. 11, November 2006.DRAFT – DELIBERATIVE – PRIV ILEGED AND CONFIDENTIAL

G. What are the estimated safety effects of the final MYs 2012-2016

CAFE and GHG standards?

The primary goals of the final CAFE and GHG standards are to reduce fuel consumption and GHG emissions, but in addition to these intended effects, the agencies must consider the potential of the standards to affect vehicle safety, which the agencies have assessed in evaluating the appropriate le vels at which to set the final standards. Safety trade-offs associated with fuel econom y increases have occurred in the past, and the agencies must be mindful ofthe possibility of future ones. These past safety tradeoffs occurred because manufacturers chose, at the time, to build smaller and lighter vehicles in response to CAFE standards rath er than adding more expensive fuel-saving technologies (and maintaining vehicle size a nd safety), and the smaller and lighter

vehicles did not fare as well in crashes as larger and heavie r vehicles. Historically, as shown in FARS data analyzed by NHTSA, the sa fest vehicles have been heavy and large, while the vehicles with the highest fatal-cr ash rates have been light and small, both because the crash rate is higher for small/light vehicles and because the fatality rate per crash is higher for small/ light vehicle crashes.

The primary mechanism in this rulemaki ng for mitigating the potential negative effects on safety is the application of f ootprint-based standards, which create a

disincentive for manufacturers to produce smaller-footprint ve hicles. Manufacturers have stated, however, that they will reduce vehicle weight as one of the cost-effective means of increasing fuel economy and reducing CO 2 emissions, and the agencies have incorporated this expectation into our modeling analysis s upporting today’s final standards. NHTSA’s previous analyses examining the relationshi p between vehicle mass and fatalities found fatality increases as vehicle weight and size were reduced, but these previous analyses did

not differentiate between we ight reductions and size ( i.e. , weight and footprint)

reductions.

The question of the effect of changes in vehicle mass on safety in the context of fuel economy is a complex question that poses serious analytic chal lenges and has been a contentious issue for many years, as discusse d by a number of commenters to the NPRM. This contentiousness arises, at least in part, from the difficu lty of isolating vehicle mass from other confounding factors ( e.g. , driver behavior, or vehicl e factors such as engine size and wheelbase). In addi tion, several vehicle factors have been closely related historically, such as vehicle mass, wheelba se, and track width. The issue has been reviewed and analyzed in the literature for more than two decades. For the reader’s reference, much more information about safe ty in the CAFE context is available in Chapter IX of NHTSA’s FRIA. Chapter 7.6 of EPA’s final RIA also contained additional discussion on mass and safety.

Over the past several years, as also di scussed by a number of commenters to the NPRM, contention has arisen with regard to the applicability of analysis of historical crash data to future safety effects due to mass reduction. The agencies recognize that there are a host of factors that may make future mass reduction different than what is reflected in the historical data. For one, th e footprint-based standards have been carefully

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developed by the agencies so that they do not encourage vehicle foot print reductions as a way of meeting the standards, but so that they do encourage application of fuel-saving technologies, including mass reduction. This in turn encourages manufacturers to find ways to separate mass reduction from footprin t reduction, which will very likely result in a future relationship between mass and fatali ties that is safer than the historical relationship. However, as manufacturers pursue these methods of mass reduction, the fleet moves further away from the historical trends, which the agencies recognize.

NHTSA’s NPRM analysis of the safety effects of the proposed CAFE standards was based on NHTSA’s 2003 report concer ning mass and size reduction in MYs 1991- 1999 vehicles, and evaluated a “worst-case scen ario” in which the safety effects of the

combined reductions of both mass and size for those vehicles were determined for the future passenger car and light truck fleets. 1 In the NPRM analysis, mass and size could not be separated from one another, resulting in what NHTSA rec ognized was a larger safety disbenefit than was likely under the MYs 2012-2016 foot print-based CAFE standards. NHTSA emphasized, however, that actual fatalities would likely be less than these “worst-case” estimates, and possibly si gnificantly less, based on the various factors

discussed in the NPRM that could reduce th e estimates, such as careful mass reduction through material substitution, etc.

For the final rule, as discussed in the NP RM and in recognition of the importance of conducting analysis that bett er reflects, within the limits of our current knowledge, the potential safety effects of future mass reduc tion in response to the final CAFE and GHG standards that is highly unlikely to involve concurrent reductions in footprint, NHTSA has revised its analysis in consultation with EPA. Perhaps the most important change has been that NHTSA agreed with commenters that it was both possibl e and appropriate to separate the effect of mass reductions from the effect of footprint reductions. NHTSA thus performed a new statistical analysis, hereafter referred to as the 2010 Kahane analysis, of the MYs 1991-99 vehicle database from its 2003 report (now including rather than excluding 2-door cars in the passenger car fleet), assessing relationships between fatality risk, mass, and footprint for both passenger cars and LTV s (light trucks and vans). 2 As part of its results, the new report presents an “upper-estimate scenario,” a “lower-estimate scenario,” as well as an “unmodified regression scenario” representing potential safety effects of future mass reductions without corr esponding vehicle size reductions, that assume, by virtue of being a cr oss-sectional analysis of historical data, that historical relationships between vehicle mass and fatalities are maintained. The “upper-estimate scenario” and “lower-es timate scenario” are based on NHTSA’s judgment as a vehicle safety agency, and are not meant to convey any more or less

likelihood in the result s, but more to convey a sense of bounding for potential safety effects. The upper-estimate sc enario reflects potential safety effects given the report’s

1 The analysis excluded 2-door cars.

2 “Relationships Between Fatality Risk, Mass, an d Footprint in Model Year 1991-1999 and Other Passenger Cars and LTVs,” Charles J. Kahane, NCSA, NHTSA, March 2010, available at Docket No. NHTSA-2009-0059-[item no.]. We note that this report has not yet been externally peer-reviewed, but that NHTSA had begun the process for peer review in accordance with OMB guidance by the time of publication of this final rule. The results of the peer review and any subsequent revisions to the report will be made available in a public docket and on NHTSA’s website as they are completed.

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finding that that, using the one-step regression method of the 2003 Kahane report, the regression coefficients show that mass and footprint each accounted for about half the fatality increase associated with downsizi ng in a cross-sectional analysis of MYs 1991-

1999 cars. A similar effect was found for li ghter LTVs. Applying the same regression method to heavier LTVs, however, the coefficients indicated a significant societal fatality reduction when mass, but not footprin t, is reduced in the heavier LTVs. 3 Fatalities are reduced primarily because mass reduction in the heavier LTVs will reduce risk to occupants of the other cars and lighter LTVs involved in collisions with these heavier

LTVs. 4 Thus, even in the “upper-estimate scen ario,” the potential fatality increases associated with mass reduction in the passenger cars would be to a large extent offset by

the benefits of mass reduc tion in the heavier LTVs.

The lower-estimate scenario, in turn, reflects NHTSA’s estimate of potential safety effects if future mass reduction is accomplished entirely by things like material substitution, smart design, 5 and component integration, among other things, that can reduce mass without perceptibly changing a vehicle’s shape, functionality, or safety performance, maintaining structural streng th without compromising other aspects of safety. If future mass reduction follows this path, it could limit the added risk close to only the effects of mass per se (the ability to transfer mome ntum to other vehicles or objects in a collision), resulting in estima ted effects in passenger cars that are substantially smaller than in the upper-estimate scenario based directly on the regression

results. The lower-estimate scenario al so covers both passenger cars and LTVs.

Overall, based on the new analyses, NHTSA estimated that fatality effects could be markedly less than those estimated in the “worst-case scenario” presented in the NPRM. The agencies believe that the overa ll effect of mass reduction in cars and LTVs may be close to zero, and may possibly be bene ficial in terms of the fleet as a whole if mass reduction is carefully applied in the futu re (as with careful material substitution and

other methods of mass reduction that can reduce mass without pe rceptibly changing a car’s shape, functionality, or safety perfor mance, and maintain its structural strength without making it excessively rigi d). This is especially impor tant if the mass reduction in the heavier LTVs is greater (in absolute te rms) than in passenger cars, as discussed further below and in the 2010 Kahane report.

3 Conversely, the coefficients indicate a signif icant increase if footprint is reduced.

4 We note that there may be some (currently non-qu antifiable) welfare losses for purchasers of these heavier LTVs, the mass of which is reduced in response to these final standards. This is due to the fact that in certain crashes, as discussed below and in greater detail in Chapter IX of the NHTSA FRIA, more mass will always be helpful (although cer tainly in other crashes, the amount of mass reduction modeled by the agency will not be enough to have any significant effect on driver/occupant safety). However, we believe the effects of this will likely be minor. Consumer welf are impacts of the final rule are discussed in more detail in Chapter VIII of the NHTSA FRIA.

5 Manufacturers implement smart design through computer aided engineering (CAE) tools that can be used to better optimize load paths within structures by reducing stresses and bending moments applied to structures. This allows better optimization of the sectional thicknesses of structural components to reduce mass while maintaining or improving the function of the component. Smart designs also integrate separate parts in a manner that reduces mass by combining functions or the reduced use of separate fasteners. In addition, some “body on frame” vehicles are re designed with a lighter “unibody” construction.

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The following sections will address how th e agencies addressed potential safety effects in the NPRM for the proposed sta ndards, how commenters responded, and the work that NHTSA has done since the NPRM to revise its estimates of potential safety

effects for the final rule. The final section discusses some of the agencies’ plans for the future with respect to potential analysis a nd studies to further e nhance our understanding of this important and complex issue.

1. What did the agencies say in the NPRM with regard to potential safety effects?

In the NPRM preceding these final standards, NHTSA’s safety assessment derived from the agency’s belief that some of these vehicle factors, namely vehicle mass and footprint, could not be accurately sepa rated. NHTSA relied on the 2003 study by Dr. Charles Kahane, which estimates the eff ect of 100-pound reductions in MYs 1991-1999 heavy light trucks and vans (LTVs), li ght LTVs, heavy passenger cars, and light

passenger cars. 6 The study compares the fatality rates of LTVs and cars to quantify differences between vehicle type s, given drivers of the same age/gender, etc. In that analysis, the effect of “weight reduction” is not limited to the effect of mass per se , but includes all the factors, such as length, width, structural strength, safe ty features, and size of the occupant compartment, that were natu rally or historically confounded with mass in

MYs 1991-1999 vehicles. The rationale was that adding length, width, or strength to a vehicle historically also made it heavier.

NHTSA utilized the relati onships between mass and safety from Kahane (2003), expressed as percentage increases in fatalities per 100-pound mass reduction, and examined the mass effects assumed in the NPRM modeling analysis. While previous CAFE rulemakings had limited mass reduction as a “technology option” to vehicles over 5,000 pounds GVWR, both NHTSA’s and EPA’ s modeling analyses in the NPRM included mass reduction of up to 5-10 percen t of baseline curb weight, depending on vehicle subclass, in response to recently-submitted manufacturer product plans as well as public statements indicating that these leve ls were possible and likely. 5-10 percent represented a maximum bound; EPA’s modeling, for example, included average vehicle weight reductions of 4 percent betw een MYs 2011 and 2016, although the average pervehicle mass reduction was greater in absolute terms for light truc ks than for passenger

cars. NHTSA’s assumptions for mass reduction were also limited by lead time such that mass reductions of 1.5 percent were include d for redesigns occurring prior to MY 2014, and mass reductions of 5-10 percent were onl y “achievable” in redesigns occurring in

MY 2014 or later. NHTSA further assumed that mass reductions would be limited to 5 percent for small vehicles ( e.g. , subcompact passenger cars), and that reductions of 10 percent would only be applied to the larger vehicle types ( e.g. , large light trucks).

6 Kahane, Charles J., Ph.D., “Vehicle Weight, Fata lity Risk and Crash Compatibility of Model Year 1991- 99 Passenger Cars and Light Trucks,” DOT HS 809 662, October 2003, Executive Summary. Available at http://www.nhtsa.dot.gov /cars/rules/regrev/eva luate/809662.html (last accessed March 10, 2010).

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Based on these assumptions of how ma nufacturers might comply with the standards, NHTSA examined the effects of the identifiable safety trends over the lifetime of the vehicles produced in each model year. The effects were estimated on a year-byyear basis, assuming that certain known safety trends would result in a reduction in the target population of fatalities from which the mass effects are derived. 7 Using this method, NHTSA found a 12.6 percent reduction in fatality levels between 2007 and 2020. The estimates derived from applying Ka hane’s 2003 percentages to a baseline of 2007 fatalities were then multiplied by 0.874 to account for changes that the agency believed would take place in passenger ca r and light truck safety between the 2007

baseline on-road fleet used for that particular analysis and year 2020.

NHTSA and EPA both emphasized that the sa fety effect estimates in the NPRM

needed to be understood in the context of th e 2003 Kahane report, which is based upon a cross-sectional analysis of the actual on-road safety e xperience of 1991-1999 vehicles. For those vehicles, heavier usually also meant larger-footprint. Hence, the numbers in those analyses were used to pr edict the safety-related fatalities that could occur in the unlikely event that weight reduction fo r MYs 2012-2016 is accomplished entirely by reducing mass and reducing footprint. Any estimat es derived from those analyses represented a “worst-case” estimate of safety effects, for several reasons.

First, manufacturers are far less likely to reduce mass by “downsizing” (making vehicles smaller overall) under the current attribute-based standards, because the standards are based on vehicle footprint. The selection of footprint as the attribute in setting CAFE and GHG standards helps to mi nimize the incentive to reduce a vehicle’s physical dimensions. This is because as footprint decreases, the corresponding fuel economy/GHG emission target becomes more stringent. 8 The shape of the footprint curves themselves have also been designed to be approximately “foot print neutral” within the sloped portion of the functions – that is, to neither encourage manufacturers to

7 NHTSA explained that there are several identifiable safe ty trends that are already in place or expected to

occur in the foreseeable future and that were not acco unted for in the study. For example, two important new safety standards that have already been issued and will be phasing in during the rulemaking time frame. Federal Motor Vehicle Safety Standard No. 126 (49 CFR 571.126) will require electronic stability control in all new vehicles by MY 2012, and the upgrade to Federal Motor Vehicle Safety Standard No. 214 (Side Impact Protection, 49 CFR 571.214) will likely result in all new vehicles being equipped with head-curtain air bags by MY 2014. 7 Additionally, the agency stated that it anticipates continued improvements in driver (and passenger) behavior, such as higher safety belt use rates. All of these will tend to reduce the absolute number of fatalities resulting from mass reductions. Thus, while the percentage increases in Kahane (2003) was applied, the reduced ba se resulted in smaller absolute increases than those that were predicted in the 2003 report.

8 We note, however, that vehicle footprint is not synonymous with vehicle size. Since the footprint is only that portion of the vehicle between the front and rear axles, footprint-based standards do not discourage downsizing the portions of a vehicle in front of the fron t axle and to the rear of the rear axle, or to other portions of the vehicle outside the wheels. The crush space provided by those portions of a vehicle can make important contributions to managing crash energy. NHTSA noted in the NPRM that at least one manufacturer has confidentially indicated plans to reduce overhang as a way of reducing mass on some vehicles during the rulemaking time frame. Additionally , simply because footprint-based standards create no incentive to downsize vehicles, do es not mean that manufacturers may no t choose to do so if doing so makes it easier to meet the overall standard (as, for exampl e, if the smaller vehicles are so much lighter that they exceed their targets by much greater amounts).

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increase the footprint of their fleets, nor to decrease it. For further discussion on these aspects of the standards, pleas e see Section II.C above and Ch apter 2 of the joint TSD. However, as discussed in Sections III.H.1 and IV.G.6 below, the agencies acknowledge some uncertainty regarding how consumer pur chases will change in response to the vehicles designed to meet the MYs 2012-2016 sta ndards. This could potentially affect the mix of vehicles sold in the future, in cluding the mass and footprint distribution.

As a result, the agencies found it likely that a significant portion of the mass

reduction in the MY 2012-2016 vehicles would be accomplished by strategies, such as material substitution, smart design, redu ced powertrain requirements, and mass compounding, that have a lesser safety effect than the prevalent 1980s strategy of simply making the vehicles smaller. The agencies noted that to the extent that future mass reductions could be achieved by these met hods—without any accompanying reduction in the size or structural strength of the vehicle— then the fatality increases associated with the mass reductions anticipated by the model as a result of the proposed standards could be significantly smaller than those in the worst-case scenario.

However, even though the agencies recognized that these methods of mass reduction could be technologically feasible in the rulemaking time frame, and included them as such in our modeling analyses, the ag encies diverged as to how potential safety effects accompanying such methods of mass reduc tion could be evaluated, particularly in relation to the worst-case scenario presented by NHTSA. NHTSA stated that it could not predict how much smaller those increases would be for any given mixture of mass reduction methods, since the data on the safe ty effects of mass re duction alone (without size reduction) was not available due to the low numbers of vehicl es in the current onroad fleet that have utilized these technologies exte nsively. Further, to the extent that mass reductions were accomplished through us e of light, high-strength materials, NHTSA emphasized that there would be signifi cant additional costs that would need to be determined and accounted for than were reflected in the agency’s proposal.

Additionally, NHTSA emphasized that wh ile it thought material substitution and

other methods of mass reduction could consider ably lessen the potential safety effects compared to the historical trend, NHTSA also st ated that it did not believe the effects in passenger cars would be smalle r than zero. EPA disagreed wi th this, and stated in the NPRM that the safety effects could very well be smaller than zero. Even though footprint-based standards disc ourage downsizing as a way of “balancing out” sales of larger/heavier vehicles, they do not discour age manufacturers from reducing crush space in overhang areas or from reducing structural support as a way of taking out mass. 9
Moreover, NHTSA’s analysis had also found th at lighter cars have a higher involvement rate in fatal crashes, even after controlling for the driver’s age, gender, urbanization, and region of the country. Being unable to explai n this clear trend in the crash data, NHTSA

stated that it must assume that mass reduction is likely to be associated with higher fatalcrash rates, no matter how the weight reduction is achieved.

9 However, we recognize that FMVSS and NCAP ratin gs may limit the manufacturer’s ability to reduce crush space or structural support.

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NHTSA also noted in the NPRM that se veral studies by Dynamic Research, Inc. (DRI) had been repeated ly cited to the agency in suppor t of the propositio n that reducing vehicle mass while maintaining track widt h and wheelbase would lead to significant safety benefits. In its 2005 studies, on e of which was published and peer-reviewed through the Society of Automotive Engineers as a technical paper, DRI attempted to assess the independent effects of vehicle weight and size (in terms of wheelbase and track width) on safety, and presente d results indicating that reduc ing vehicle weight tends to reduce fatalities, but that reducing vehicle wheelbase and track wi dth tends to increase fatalities. DRI’s analysis was based on FARS data for MYs 1985-1998 passenger cars and 1985-1997 light trucks, similar to the MY s 1991-1999 car and truck data used in the 2003 Kahane report. However, DRI include d 2-door passenger cars, while the 2003 Kahane report excluded those vehicles out of concern that their incl usion could bias the results of the regression analysis, beca use a significant proportion of MYs 1991-1999 2- door cars were sports and “muscle” cars, which have particularly high fatal crash rates for their relatively short wheelbases compared to the rest of the fleet. While in the NPRM NHTSA rejected the results of the DRI studies based in part on this concern, the agencies note that upon further consideration, NHTSA has agreed for this final rule that the inclusion of 2-door cars in regr ession analysis of historical data is appropriate, and indeed has no overly-biasing effects.

The 2005 DRI studies also differed from th e 2003 Kahane report in terms of their estimates of the effect of vehicle weight on rollover fatalities. The 2003 Kahane report analyzed a single variable, curb weight, as a surrogate for both ve hicle size and weight, and found that curb weight reductions would increase rollover fatal ities. The DRI study, in contrast, attempted to analyze curb wei ght, wheelbase, and track width separately, and found that curb weight reduction would decrease rollover fatalities, while wheelbase

reduction and track width reduction would incr ease them. DRI suggested that heavier vehicles may have higher rollover fatalities for two reasons: first, because taller vehicles tend to be heavier, so the correlation betw een vehicle height a nd weight and vehicle center-of-gravity height may make heavier vehicles more rollover-prone; and second, because heavier vehicles may have been less rollover-crashworthy due to FMVSS No. 216’s constant (as opposed to proportional) requirements for MYs 1995-1999 vehicles weighing more than 3,333 lbs unloaded.

Overall, DRI’s 2005 studies found a reduction in fatalities for car s (580 in the first study, and 836 in the second study) and for tr ucks (219 in the fi rst study, 682 in the second study) for a 100 pound reduction in curb weight without accompanying wheelbase or track width reductions. In the NPRM, NHT SA disagreed with the results of the DRI studies, out of concern that DRI’s inclusion of 2-door cars in its analysis biased the results, and because NHTSA was unable to reproduce DRI’s results despite repeated attempts. NHTSA stated that it agreed intu itively with DRI’s conclusion that vehicle mass reductions without accompanying size re ductions (as through substitution of a heavier material for a lighter one) would be less harmful than dow nsizing, but without supporting real-world data and unable to verify DRI’s results, NHTSA stated that it could

not conclude that mass reductions would result in safety benefits. EPA, in contrast, believed that DRI’s results contained some merit, in particular because the study

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separated the effects of mass and size and EPA stated that applying them using the curb weight reductions in EPA’s modeling analys is would show an overall reduction of fatalities for the proposed standards.

On balance, both agencies recognized th at mass reduction could be an important tool for achieving higher levels of fuel economy and reducing CO 2 emissions, and emphasized that NHTSA’s fatality estimates represented a worst-case scenario for the potential effects of the proposed standards, and that actual fatalities wi ll be less than these estimates, possibly significantly less, based on the various factors discussed in the NPRM that could reduce the estimates. The agencies sought comment on the safety analysis and discussions presented in the NPRM.

2. What public comments did the agencie s receive on the safety analysis

and discussions in the NPRM?

Several dozen commenters addressed the sa fety issue. Comments in response to the safety effects analysis and discussion in the NPRM tended to follow several general themes, as follows:

• NHTSA’s safety effects estimates are in accurate because they do not account for

the fact that:

o While NHTSA’s study only consider s vehicles from MYs 1991-1999, more recently-built vehicles are safer than those, and future vehicles will be safer still;

o Lighter vehicles are safer than heavie r cars in terms of crash-avoidance, because they handle and brake better;

o Fatalities are linked more to other factors than mass;

o The structure of the standards redu ces/contributes to potential safety effects from mass reduction;

o NHTSA could mitigate additional safety effects from mass reduction, if there are any, by simply regulating safety more;

o Casualty risks range widely for vehicles of the same wei ght or footprint, which skews regression analysis and makes computer simulation a better predictor of the safety effects of mass reduction;

• DRI’s analysis shows that lighter vehicles will save lives, and NHTSA reaches the opposite conclusion without disproving DRI’s analysis;

o Reasons that NHTSA and DRI may ha ve reached different conclusions:

 NHTSA’s study should distinguish be tween reductions in size and reductions in weight like DRI’s;

 NHTSA’s study should include two-door cars;

 NHTSA’s study should have used different assumptions;

 NHTSA’s study should include confidence intervals;

• NHTSA should include a “best-cas e” estimate in its study;

• NHTSA should not include a “worst -case” estimate in its study;

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The agencies recognize that the issue of the potential safety effects of mass reduction, which was one of the many factors co nsidered in the balancing that led to the agencies’ conclusion as to appropriate stringency levels for the MYs 2012-2016 standards, is of great interest to the public and could possibly be a more significant factor in regulators’ and manufacturer s’ decisions with regard to future standards beyond MY 2016. The agencies are committed to analyz ing this issue thoroughly and holistically going forward, based on the best available science, in order to further their closely related missions of safety, energy conservation, a nd environmental protection. We respond to

the issues and concerns raised by commenters in turn below.

NHTSA’s estimates are inaccurate because NHTSA’s study only considers vehicles from MYs 1991-1999, but more recently-built ve hicles are safer than those, and future vehicles will be safer still

A number of commenters (CAS, Adcoc k, NACAA, NJ DEP, NY DEC, UCS, and Wenzel) argued that the 2003 Kahane report, on which the “worst-case scenario” in the NPRM was based, is outdated because it c onsiders the relationship between vehicle weight and safety in MYs 1991-1999 passenger ca rs. These commenters generally stated that data from MYs 1991-1999 vehicles prov ide an inaccurate basis for assessing the relationship between vehicle weight and safety in current or future vehicles, because the

fleets of vehicles now and in the future ar e increasingly different from that 1990s fleet (more crossovers, fewer trucks, lighter trucks , etc.), with different vehicle shapes and characteristics, different materials, and more safety features. Several of these commenters argued that NHTSA should conduct an updated analysis for the final rule using more recent data – Wenzel, for example, stated that an updated regression analysis

that accounted for the recent introduction of crossover S UVs would likely find reduced casualty risk, similar to DRI’s previous findi ng using fatality data. CEI, in contrast, argued that the “safety trade-off” would not be eliminated by new technologies and attribute-based standards, because additional weight inherently makes a vehicle safer to its own occupants, citing the 2003 Kahane repo rt, while AISI argued that Desapriya had found that passenger car drivers and occupants are two times more likely to be injured than drivers and occupants in larger pickup trucks and SUVs.

Several commenters (Adcock, CARB, Daimler, NESCAUM, NRDC, Public Citizen, UCS, Wenzel) suggested that NHTSA’s analysis was based on overly pessimistic assumptions about how manufact urers would choose to reduce mass in their vehicles, because manufacturers have a strong incentive in the market to build vehicles safely. Many of these commenters stated that several manufactu rers have already committed publicly to fairly ambitious mass reduction goals in the mid-term, but several

stated further that NHTSA should not assume that manufacturers will reduce the same

amount of mass in all vehicles , because it is likely that they will concentrate mass reduction in the heaviest vehicles, which will improve compatibility and decrease aggressivity in the heaviest vehicles. Daim ler emphasized that all vehicles will have to comply with the Federal Motor Vehicle Safety Standards, and will likely be designed to

test well in NHTSA’s NCAP tests.

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Other commenters (Aluminu m Association, CARB, CAS, ICCT, MEMA, NRDC, U.S. Steel) also emphasized the need for NHTSA to account for the safe ty benefits to be expected in the future from use of advan ced materials for lightweighting purposes and other engineering advances. The Aluminum Association stated that advanced vehicle design and construction techniques using alum inum can improve energy management and minimize adverse safety effects of their use, 10 but that NHTSA’s safety analysis could

not account for those benefits if it were based on MYs 1991-1999 vehicles. CAS, ICCT,

and U.S. Steel discussed similar benefits for more recent and future vehicles built with high strength steel (HSS), although U.S. Steel cautioned that gi ven the stringency of the proposed standards, manufacturers would lik ely be encouraged to build smaller and lighter vehicles in order to achieve compliance, which fare worse in head-on collisions than larger, heavier vehicles. AISI, in contrast to U.S. Steel, stated that in its research with the Auto/Steel Partnership and in pr ograms supported by DOE, it had found that the use of new Advanced HSS steel grades could enable mass of critical crash structures, such as front rails and bumper systems, to be reduced by 25 per cent without degrading performance in standard NHTSA frontal or IIHS offset instrumented crash tests compared to their “heavier counterparts.”

Agencies’ response:

NHTSA, in consultation with EPA and DOE, plans to begin updating the MYs 1991-1999 database on which NHTSA’s safety anal yses in the NPRM and final rule are

based in the next several mont hs in order to analyze the differences in safety effects against vehicles built in more recent model years. As this task will take at least a year to complete, beginning it immediately after the NPRM would not have enabled the agency to complete it and then conduct a new analys is during the period between the NPRM and

the final rule.

For purposes of this final rule, however, we believe that using the same MYs

1991-1999 database as that used in the 2003 Ka hane study provides a reasonable basis for attempting to estimate safety effects due to re ductions in mass. While commenters often stated that updating the database would help to reveal the effect of recently-introduced lightweight vehicles with extensive material substitution, there have in fact not yet been a significant number of vehicles with substantial mass reduction/material substitution to analyze, and they must also show up in the crash databases for NHTSA to be able to add them to its analysis. Based on NHTSA’s research, specifically, on three statistical analyses over a 12-year period (1991-2003) covering a range of 22 model years (1978- 1999), NHTSA believes that the relationships between mass, size, and safety has only changed slowly over time, alt hough we recognize that they may change somewhat more

10 The Aluminum Association (NHTSA-2009-0059-0067.3) stated that its research on vehicle safety compatibility between an SUV and a mid-sized car, done jointly with DRI, shows that reducing the weight of a heavier SUV by 20% (a realistic value for an aluminum-intensive vehicle) could reduce the combined injury rate for both vehicles by 28% in moderately severe crashes. The commenter stated that it would keep NHTSA apprised of its results as its research progressed. Based on the information presented, NHTSA believes that this research appears to agree with NHTSA’s latest analysis, which finds that a reduction in weight for the heaviest vehicles may improve overall fleet safety.

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rapidly in the future. 11 As the on-road fleet gains incr easing numbers of vehicles with increasing amounts of different methods of mass reduction applied to them, we may begin to discern changes in th e crash databases due to the presence of these vehicles, but any such changes are likely to be slow and evolutionary, part icularly in the context of MYs 2000-2009 vehicles. The agencies do expect th at further analysis of historical data files will continue to provide a robust and practicable basis for estimating the potential safety effects that might occur with future reductions in vehicle mass. However, we recognize that estimates derived from analysis of historical data, like estimates from any other type of analysis (inc luding simulation-based analysis , which cannot feasibly cover all relevant scenarios), will be uncertain in terms of predicting actual future outcomes with respect to a vehicle fl eet, driving population, and operating environment that does not yet exist.

The agencies also recognize that more re cent vehicles have more safety features than 1990s vehicles, which are likely to make them safer overall. To account for this, NHTSA did adjust the results of both its NPRM and final rule analysis to include known safety improvements, like ESC and increases in seat belt use, that have occurred since

MYs 1991-1999. 12 However, simply because newer vehicles have more safety countermeasures, does not mean that the weight /safety relationship necessarily changes. More likely, it would change the target populat ion (the number of fatalities) to which one would apply the weight/safety relationship. Thus, we still beli eve that some mass reduction techniques for both passenger cars and light trucks can make them less safe, in

certain crashes as discussed in NHTSA’s FRIA, than if mass had not been reduced. 13

As for NHTSA’s assumptions about ma ss reduction, in its analysis, NHTSA generally assumed that lighter vehicles coul d be reduced in weight by 5 percent while heavier light trucks could be reduced in we ight by 10 percent. NHTSA recognizes that manufacturers might choose a different mass reduction scheme than this, and that its quantification of the estimate d effect on safety would be different if they did. We emphasize that our estimates are based on th e assumptions we have employed and are intended to help the agency consider the poten tial effect of the final standards on vehicle safety. Thus, based on the 2010 Kahane analys is, reductions in weight for the heavier

11 NHTSA notes the CAS’ comments regarding changes in the vehicle fleets since the introduction of CAFE standards in the late 1970s, but believes they apply more to the differences between late 1970s through 1980s vehicles and 2010s vehicles than to the differences between 1990s and 2010s vehicles.

NHTSA believes that the CAS commen ts regarding the phase-out of 1970 s vehicles and their replacement with safer, better fuel-economy-achieving 1980s vehicles paint with rather too large a brush to be relevant to the main discussion of whether the 2003 Kahane report database can reasonably be used to estimate safety effects of mass reduction for the MYs 2012-2016 fleet.

12 See NHTSA FRIA Chapter IX.

13 If one has a vehicle (vehicle A), and both reduces the vehicle’s mass and adds new safety equipment to it, thus creating a variant (vehicle A 1 ), the variant might conceivably have a level of overall safety for its occupants is equal to that of the original vehicle (vehicle A). However, vehicle A 1 might not be as safe as second variant (vehicle A 2 ) of vehicle A, one that is produced by adding to vehicle A the same new safety equipment added to the first variant, but this time without any mass reduction.

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light trucks would have positive overall safety effects, 14 while mass reductions for passenger cars and smaller light trucks would have negative overall safety effects.

NHTSA’s estimates are inaccurate because they do not account for the fact that lighter vehicles are safer than heavie r cars in terms of crash-avoidance, because they handle and brake better

ICCT stated that lighter vehicles are be tter able to avoid cr ashes because they “handle and brake slightly better,” arguing th at size-based standards encourage lighterweight car-based SUVs with “significantly better handling and crash protection” than 1996-1999 mid-size SUVs, which will reduce both fa talities and fuel consumption. ICCT stated that NHTSA did not include these safety benefits in its analys is. DRI also stated that its 2005 report found that crash avoidance improves with reduction in curb weight

and/or with increases in wheelbase and track, because “Crash avoidance can depend, amongst other factors, on the vehicle direc tional control and roll over characteristics.” DRI argued that, therefore, “The se results indicate that vehi cle weight reduction tends to decrease fatalities, but vehicle wheelbase and track reduction tends to increase fatalities.”

Agencies’ response:

In fact, NHTSA’s regression analysis of crash fatalities per million registration years measures the effects of crash a voidance, if there are any, as well as

crashworthiness. Given that the historical empirical data for passenger cars show a trend of higher crash rates for lighter cars, it is unc lear whether lighter cars have, in the net, superior crash avoidance, although the agencies recognize that they may have advantages in certain individual situations. EPA pr esents a discussion of improved accident avoidance as vehicle mass is reduced in Chapte r 7.6 of its final RIA. The important point to emphasize is that it depends on the situa tion – it would oversimplify drastically to point to one situation in whic h extra mass helps or hurts and then extrapolate effects for crash avoidance across the board based on only that.

For example, the relationship of vehicle mass to rollover and directional stability is more complex than commenters imply. For rollover, it is true th at if heavy pickups were always more top-heavy than lighter pi ckups of the same f ootprint, their higher center of gravity could make them more roll over-prone, yet some mass can be placed so as to lower a vehicle’s center of gravit y and make it less rollover-prone. For mass

reduction to be beneficial in rollover crashes, then, it must take center of gravity height into account along with other factors su ch as passenger compartment design and structure, suspension, the presence of vari ous safety equipment, and so forth.

Similarly, for directional stability, it is true that having more mass increases the “understeer gradient” of cars – i.e. , it reinforces their tendency to proceed in a straight line and slows their response to steering input, which would be harmful where prompt steering response is es sential, such as in a double-la ne-change maneuver to avoid an

14 This is due to the beneficial effect on the occupants of vehicles struck by the downweighted larger

vehicles.

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obstacle. Yet more mass and a higher understeer gradient could help when it is better to remain on a straight path, such as on a straight road with icy patches where wheel slip might impair directional stability. Thus, wh ile less vehicle mass can sometimes improve crash avoidance capability, there can also be situations when more vehicle mass can help

in other kinds of crash avoidance.

Further, NHTSA’s research suggests that additional vehicle mass may be even more helpful, as discussed in Chapter IX of NHTSA’s FRIA, when the average driver’s response to a vehicle’s maneuverability is taken into account. Lighter cars have historically (1976-2009) had higher collision-invo lvement rates than heavier cars – even

in multi-vehicle crashes where directional and rollover stability is not particularly an

issue. 15 Based on our analyses using nationally-c ollected FARS and GES data, drivers of lighter cars are more likely to be the culpable party in a 2-vehicle collision, even after controlling for footprint, the dr iver’s age, gender, urbanizatio n, and region of the country.

Thus, based on this data, it a ppears that lighter cars may not be driven as well as heavier cars, although it is unknown why this is so. If poor drivers intrinsically chose light cars (self-selection), it might be eviden ced by an increase in antisocial driving behavior (such as DWI, drug involvement, sp eeding, or driving wit hout a license) as car weight decreases, after controlli ng for driver age and gender – in addition to the increases in merely culpable driver behavior (such as failure to yield the right of way). But analyses in NHTSA’s 2003 report did not show an increase in antisocial driver behavior in the lighter cars paralleling their increase in culpable involvements.

NHTSA also hypothesizes that certain asp ects of lightness and/or smallness in a car may give a driver a perception of greater maneuverability that ultimately results in driving with less of a “safety margin,” e.g. , encouraging them to weave in traffic. That may appear paradoxical at first glance, as ma neuverability is, in the abstract, a safety plus. Yet the situation is not unlike powerful engines that could theoretically enable a driver to escape some hazards, but in reality have long been associated with high crash and fatality rates. 16

NHTSA’s estimates are inaccurate because fatalities are linked more to other factors than mass

Tom Wenzel stated that the safety record of recent model year crossover SUVs indicates that weight reduction in this class of vehicles (small to mid-size SUVs) resulted

15 See

, e.g. , NHTSA (2000). Traffic Safety Facts 1999. Report No. DOT HS 809 100. Washington, DC: National Highway Traffic Safety Administration, p. 71; Najm, W.G., Sen, B., Smith, J.D., and Campbell, B.N. (2003). Analysis of Light Vehicle Crashes and Pre-Crash Scenarios Based on the 2000 General Estimates System, Report No. DOT HS 809 573. Washington, DC: National Highway Traffic Safety Administration, p. 48.

16 Robertson, L.S. (1991), “How to Save Fuel and Reduce Injuries in Automobiles,” The Journal of

Trauma , Vol. 31, pp. 107-109; Kahane, C.J. (1994). Corre lation of NCAP Performance with Fatality Risk in Actual Head-On Collisions, NHTSA Technical Report No. DOT HS 808 061. Washington, DC: National Highway Traffic Sa fety Administration, http://www-nrd. nhtsa.dot.gov/Pubs/808061.PDF, pp. 4-

7.

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in a reduction in fatality risk. Wenzel ar gued that NHTSA should ac knowledge that other vehicle attributes may be as important, if not more important, than vehicle weight or footprint in terms of occupant safety, su ch as unibody construction as compared to ladder-frame, lower bumpers, and less rigi d frontal structures, all of which make crossover SUVs more compatible w ith cars than truck-based SUVs.

Marc Ross commented that fatalities are li nked more strongly to intrusion than to mass, and stated that research by safety expe rts in Japan and Europe suggests the main cause of serious injuries and deaths is in trusion due to the failure of load-bearing elements to properly protect occupants in a severe crash. Ross argued that the results from this project have “overturned the original views about compatibility,” which thought that mass and the mass ratio were the dominant factors. Since footprint-based standards will encourage the reduction of vehicle we ight through materials substitution while maintaining size, Ross stated, they will he lp to reduce intrusion and consequently fatalities, as the lower weight reduces crash forces while maintaining size preserves crush space. Ross argued that this factor was not considered by NHTSA in its discussion of safety. ICCT agreed with Ross’ comments on this issue.

In previous comments on NHTSA rulemakings and in several studies, Wenzel and Ross have argued generally that vehicle desi gn and “quality” is a much more important determinant of vehicle safety than mass. In comments on the NPRM, CARB, NRDC, Sierra Club, and UCS echoed this theme.

ICCT commented as well that fatality rate s in the EU are much lower than rates in the U.S., even though the vehicles in the EU fleet tend to be smaller and lighter than those in the U.S. fleet. Thus, ICCT argued, “This strongly supports the idea that vehicle and highway design are far more important factors than size or weight in vehicle safety.” ICCT added that “It also suggest s that the rise in SUVs in th e U.S. has not helped reduce fatalities.” CAS also commented that Germany’s vehicle fleet is both smaller and lighter than the American fleet, and has lower fatality rates.

Agencies’ response:

NHTSA and EPA agree that there are many features that affect safety. While crossover SUVs have lower fatality rates th an truck-based SUVs, there are no analyses that attribute the improved safety to mass alone , and not to other factors such as the lower center of gravity or the unibody construction of these vehicles. While a number of improvements in safety can be made, they do not negate the pote ntial that another 100 lbs. could make a passenger car or crossover vehicle safer for its occupants, because of the effects of mass per se as discussed in NHTSA’s FRIA, albeit similar mass reductions

could make heavier LTVs safer to other vehi cles without necessarily harming their own drivers and occupants. Moreover, in th e 2004 response to docket comments, NHTSA explained that the significant relationship betw een mass and fatality risk persisted even after controlling for vehicle pr ice or nameplate, suggesting th at vehicle “quality” as cited by Wenzel and Ross is not necessarily more important than vehicle mass.

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As for reductions in intrusions due to material substitution, the agencies agree generally that the use of new and innovative materials may have the potential to reduce crash fatalities, but such vehicles have not been introduced in large numbers into the vehicle fleet. The agencies will continue to monitor the situati on, but ultimately the

effects of different methods of mass reduction on overall safety in the real world (not just in simulations) will need to be analyzed when vehicles with these types of mass reduction

are on the road in sufficient quantities to provide statisti cally significant results. For example, a vehicle that is designed to be much stiffer to reduce intrusion is likely to have a more severe crash pulse and thus impose gr eater forces on the occupants during a crash, and might not necessarily be good for elderly an d child occupant safety in certain types

of crashes. Such trade-offs make it difficult to estimate overall re sults accurately without real world data. The agencies will continue to evaluate and analyze such real world data as it becomes available, and will keep th e public informed as to our progress.

ICCT’s comment illustrates the fact that different vehicle fleets in different countries can face different challenges. NHTSA does not believe that the fact that the EU vehicle fleet is generally light er than the U.S. fleet is th e exclusive reason, or even the primary factor, for the EU’s lower fatality ra tes. Significant differences exist in belt usage, drunk driving, rural/urban roads, driving culture, etc.

The structure of the standards reduces/contr ibutes to potential safety risks from

mass reduction

Since switching in 2006 to setting attri bute-based light truc k CAFE standards, NHTSA has emphasized that one of the benefits of a footprint-based standard is that it discourages manufactur ers from building smaller, less safe vehicles to achieve CAFE compliance by “balancing out” their larger ve hicles, and thus avoids a negative safety consequence of increasing CAFE stringency. 17 Some commenters on the NPRM (Daimler, IIHS, NADA, NRDC, Sierra Club et al. ) agreed that footpr int-based standards would protect against downsizing and help to mitigate safety risks, while others stated that there would still be safety risks even with footprint-based standards – CEI, for example, argued that mass reduction inheren tly creates safety risks, while IIHS and Porsche expressed concern about footprint-ba sed standards encouraging manufacturers to manipulate wheelbase, which could reduce cr ush space and worsen vehicle handling.

U.S. Steel and AISI both commented that the “aggressive schedule” for the proposed increases in stringency could encourage manufac turers to build smaller, lighter vehicles in order to comply.

Some commenters also focused on the shape and stringency of the target curves and their potential effect on ve hicle safety. IIHS agreed wi th the agencies’ tentative decision to cut off the target curves at th e small-footprint end. Although the agencies’

17 We note that commenters were divided on whethe r they believed there was a clear correlation between vehicle size/weight and safety (CEI, Congress of R acial Equality, Heritage Foundation, IIHS, Spurgeon, University of PA Environmental Law Project) or whether they believed that the correlation was less clear, for example because they believed that vehicle design was more important than vehicle mass (CARB, Public Citizen).

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did so in relation to concerns about the feasib ility of attribute-base d standards as applied to manufacturers emphasizing small vehicles , IIHS’s comments suggest IIHS is not

concerned with the standards’ resultant neutra lity with respect to incremental reductions in the size of the smallest vehicles. Regardi ng the safety effect of the curves requiring less stringent targets for larger vehicles, while IIHS stated that increasing footprint is good for safety, CAS, Wenzel, and the UCSB st udents stated that decreasing footprint may be better for safety in terms of risk to occupants of other vehicles. Daimler, Wenzel, and the University of PA Environmental La w Project commented ge nerally that more similar passenger car and light truck targets at identical footprints (as Wenzel put it, a single target curve) would improve fleet comp atibility and thus, safety, by encouraging manufacturers to build more passeng er cars instead of light trucks.

Agencies’ response:

The agencies continue to believe that f ootprint-based standards help to mitigate potential safety risks from downsizing if th e target curves maintain sufficient slope, because, based on NHTSA’s analysis, larger-footprint vehicles are safer than smallerfootprint vehicles. 18 Nevertheless, we recognize that footprint-based standards are not a panacea – NHTSA’s analysis continues to show that there was a historical relationship between lower vehicle mass and increased safety risk in passenger cars even if footprint is maintained, and there are ways that manuf acturers may increase footprint that either improve or reduce vehicle safety, as indicated by IIHS and Porsche.

With regard to whether the agencies should set separate curves or a single one,

NHTSA also notes in Section II.C that EP CA requires NHTSA to establish standards separately for passenger cars and light trucks, and thus concludes that the standards for

each fleet should be based on the characteristics of vehicles in each fleet. In other words, the passenger car curve should be based on th e characteristics of passenger cars, and the light truck curve should be base d on the characteristics of ligh t trucks—thus to the extent that those characteristics are different, an artificially-forced convergence would not accurately reflect those differences. Howeve r, such convergence could be appropriate depending on future trends in the light vehi cle market, specifically further reduction in the differences between passenger car and light truck characteristics. While that trend was more apparent when car-like 2WD SUVs were classified as light trucks, it seems likely to diminish for the model year vehicles subject to thes e rules as the truck fleet will be more purely “truck-like” than ha s been the case in recent years.

NHTSA’s estimates are inaccurate b ecause NHTSA could mitigate additional safety risks from mass reduction, if ther e are any, by simply regulating safety

more

Since NHTSA began considering the potenti al safety risks from mass reduction in response to increased CAFE standards, so me commenters have suggested that NHTSA could mitigate those safety risks, if any, by simply regulating more. 19 In response to the

18 See Chapter IX of NHTSA’s FRIA.

19 See, e.g. , MY 2011 CAFE final rule, 74 Fed. Reg. at 14403-05 (Mar. 30, 2009).

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safety analysis presented in the NPRM, se veral commenters stated that NHTSA should develop additional safety regulations to requ ire vehicles to be designed more safely, whether to improve compatibility (Adcock, NY DEC, Public Citizen, UCS), to require seat belt use (CAS, UCS), to improve rollover and roof crush resistance (UCS), or to improve crashworthiness generally by streng thening NCAP and the star rating system (Adcock). Wenzel commented further that “I mprovements in safety regulations will have a greater effect on occupant safety than FE st andards that are struct ured to maintain, but may actually increase, vehicle size.”

Agencies’ response:

NHTSA appreciates the commenters’ sugge stions and notes that the agency is continually striving to improve motor vehicle safety consistent with its mission. As noted above, improving safety in other areas a ffects the target population that the mass/footprint relationship could affect, but it does not necessarily change the relationship.

The 2010 Kahane analysis discussed in this final rule evaluates the relative safety risk when vehicles are made lighter than th ey might otherwise be absent the final MYs

2012-2016 standards. It does cons ider the effect of known safe ty regulations as they are projected to affect the target population.

Casualty risks range widely for vehicles of the same weight or footprint, which skews regression analysis and makes co mputer simulation a better predictor of the safety effects of mass reduction

Wenzel commented that he had found, in his most recent work, after accounting for drivers and crash location, that there is a wide range in casu alty risk for vehicles with the same weight or footprint. Wenzel stated that for drivers, casua lty risk does generally decrease as weight or footprin t increases, especially for pa ssenger cars, but the degree of variation in the data for vehicles (particularl y light trucks) at a give n weight or footprint makes it difficult to say that a decrease in weight or footprint will necessarily result in increased casualty risk. In terms of risk im posed on the drivers of other vehicles, Wenzel stated that risk increases as light truck weight or f ootprint increases.

Wenzel further stated that because a re gression analysis can only consider the average trend in the relations hip between vehicle weight/siz e and risk, it must “ignore”

vehicles that do not follow that trend. We nzel therefore recommended that the agency employ computer crash simulations for analyz ing the effect of vehicle weight reduction on safety, because they can “pinpoint the eff ect of specific vehicl e designs on safety,”

and can model future vehicles which do not yet exist and are not bound to analyzing historical data. Wenzel cited, as an example, a DRI simulation study commissioned by the Aluminum Association (Kebschull 2004), wh ich used a computer model to simulate the effect of changing SUV mass or footprin t (without changing other attributes of the vehicle) on crash outcomes, and showed a 15 percent net decrease in injuries, while

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increasing wheelbase by 4.5 inches while main taining weight showed a 26 percent net decrease in serious injuries.

Agencies’ response:

The agencies have reviewed Mr. Wenzel’s draft report for DOE to which he referred in his comments, but based on NHTSA ’s work do not find such a wide range of safety risk for vehicles with the same wei ght, although we agree there is a range of risk for a given footprint. Wenzel found that for drivers, casualty risk does generally decrease as weight or footprint increas es, especially for passenger cars, and that in terms of risk imposed on the drivers of other vehicles, risk increases as light truc k weight or footprint increases, but concluded that the variation in the data precluded the possibility of drawing any conclusions. In the 2010 Kahane study presented in the FRIA, NHTSA undertook a similar analysis in which it correlated weight to fatality risk for vehicles of essentially the same footprint. 20 The “decile analysis,” provided as a check on the trend/direction of NHTSA’s regression analysis, shows that fata lity risk generally increases and rarely decreases for lighter relative to heavier cars of the same footprint. Thus, while Mr. Wenzel was reluctant to draw a conclusion, NHTSA believes that bo th our research and Mr. Wenzel’s appear to point to the same conc lusion. We agree that there is a wide range in casualty risk among cars of th e same footprint, but we find that that casualty risk is correlated with weight. The correlation s hows that heavier car s have lower overall fatality rates than lighter cars of very similar footprint.

The agencies agree that simulation can be beneficial in certain circumstances. NHTSA cautions, however, that it is difficult fo r a simulation analysis to capture the full range of variations in crash s ituations in the way that a statistical regression analysis does. Vehicle crash dynamics are complex, a nd small changes in initial crash conditions (such as impact angle or closing speed) can have large effects on injury outcome. This condition is a consequence of variations in the deformation mode of individual components ( e.g. , buckling, bending, crushing, material failure, etc.) and how those

variations affect the creation and destruction of load paths between the impacting object and the occupant compartment during the crash ev ent. It is therefore difficult to predict

and assess structural interact ions using computational methods when one does not have a detailed, as-built geometric and material model. Even when a complete model is available, prudent engineeri ng assessments require extensiv e physical testing to verify crash behavior and safety. Despite all this , the agencies recognize that detailed crash simulations can be useful in estimating the relative structural effects of design changes over a limited range of crash conditions, and w ill continue to evaluate the appropriate use

of this tool in the future.

Simplified crash simulations can also be valuable tools, but only when employed as part of a comprehensive analytical program. They are especially valuable in evaluating the relative effect and associated confidence intervals of feasible design

20 Sections 2.4 and 3.3 of new report.

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alternatives. For example, the method employed by Nusholtz et al

. 21 could be used by a vehicle designer to estimate the benefit of incremental changes in mass or wheelbase as well as the tradeoffs that might be made betw een them once that designer has settled on a preliminary design. A key difference between th e research by Nusholtz and the research by Kebschull that Mr. Wenzel cited 22 is in their suggested applications. The former is useful in evaluating proposed alternatives early in the design process – Nusholtz specifically warns that the model provides only “general insights into the overall risk ... and cannot be used to obtain specific res ponse characteristics.” Mr . Wenzel implies the latter can “isolate the effect of specific de sign changes, such as weight reduction” and thus quantify the fleet-wide effect of substa ntial vehicle redesigns. Yet while Kebschull reports injury reductions to three significant digits, there is no validation that vehicle structures of the proposed weight and stiffness are even feasible w ith current technology. Thus, while the agencies agree that computer simulations can be useful tools, we also recognize the value of st atistical regression analysis for determining fleet-wide effects, because it inherently incorporat es real-world factors in historical safety assessments.

DRI’s analysis shows that lighter vehicl es will save lives, and NHTSA reaches the opposite conclusion without disproving DRI’s analysis

The difference between NHTSA’s results and DRI’s results for the relationship between vehicle mass and vehicle safety has be en at the crux of th is issue for several years. While NHTSA offered some theories in the NPRM as to why DRI might have found a safety benefit for mass reduction, NHTSA ’s work since then has enabled it to identify what we believe is the most likely reason for DRI’s findings . The potential near multicollinearity of the variables of curb wei ght, track width, and wheelbase creates some degree of risk that any regression models with those variables could inaccurately calibrate their effects. However, based on its own experience with statistical analysis, NHTSA believes that the specific two-step regression model used by DRI increases this risk, because it weakens relationships between curb weight and dependent variables by splitting the effect of curb weight across the two regression steps.

21 Nusholtz, G.S., G. Rabbiolo, and Y. Shi, “Estimat ion of the Effects of Vehi cle Size and Mass on CrashInjury Outcome Through Parameterized Probability Ma nifolds,” Society of Automotive Engineers (2003),

Document No. 2003-01-0905. Available at http://www.sae.org/technical/papers/2003-01-0905 (last accessed Feb. 15, 2010).

22 Mr. Wenzel cites the report by Kebschull et al [ 2004, DRI-TR-04-04-02] as an example of what he regards as the effective use of computer crash simulation. NHTSA does not concur that this analysis represents a viable analytical method for evaluating the fleet-wide tradeoffs between vehicle mass and societal safety. The simulation me thod employed was not a full finite element representation of each major structural component in the vehicles in question. Instead, an Articulated Total Body (ATB) representation was constructed for each of two representative vehicles. In the ATB model, large structural subsystems were represented by a single ellipsoid. Consolidated lo ad-deflection properties of these subsystems and the joints that tie them together were “calibrated” for an ATB vehicle model by requiring that it reproduce the acceleration pulse of a physical NHTSA crash test. NH TSA notes that vehicle si mulation models that are calibrated to a single crash test configuration ( e.g. , a longitudinal NCAP test into a rigid wall) are often illequipped to analyze alternative crash scenarios ( e.g. , vehicle-to-vehicle crashes at arbitrary angles and lateral offsets).

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The comments below are in response to NHTSA’s theories in the NPRM about

the source of the differences between NHTSA’s and DRI’s results. The majority of them are answered more fully in the 2010 Kahane report included in NHT SA’s FRIA, but we respond to them in this document as well for purposes of completeness.

NHTSA and DRI may have reached diffe rent conclusions because NHTSA’s study does not distinguish between reductio ns in size and reductions in weight

like DRI’s

Several commenters (CARB, CBD, EDF, ICCT, NRDC, and UCS) stated that DRI had been able to separate the effect of si ze and weight in its anal ysis, and in so doing proved that there was a safety benefit to reducing weight without reducing size. The commenters suggested that if NHTSA properly distinguished between reductions in size and reductions in weight, it would find the same result as DRI.

Agencies’ response:

In the 2010 Kahane analysis presented in the FRIA, NHTSA did attempt to separate the effects of vehi cle size and weight by performi ng regression analyses with footprint (or alternatively track width and wheelbase) and curb we ight as separate independent variables. For passenger cars, NHTSA found that the regressi ons attribute the fatality increase due to dow nsizing about equally to mass and footprint – that is, the effect of reducing mass alone is abou t half the effect of reducing mass and reducing footprint. Unlike DRI’s results, NHTSA’s regressions for passenger cars and for lighter LTVs did not find a safety benefit to reduc ing weight without reducing size; while NHTSA did find a safety benefit for reducing weight in the heaviest LTVs, the magnitude of the benefit as compared to DRI’s was significantly smaller. NHTSA believes that these differences in results may be an artifact of DRI’s two-step regression model, as explained above.

NHTSA and DRI may have reached diffe rent conclusions because NHTSA’s study does not include two-door cars like DRI’s

One of NHTSA’s primary theories in the NPRM as to why NHTSA and DRI’s

results differed related to DRI’s inclusion in its analysis of 2-door cars. NHTSA had excluded those vehicles from its analys is on the grounds that 2-door cars had a disproportionate crash rate (perhaps due to their inclusion of musc le and sports cars) which appeared likely to skew the regre ssion. Several commenters argued that NHTSA

should have included 2-door car s in its analysis. DRI and James Adcock stated that 2-

door cars should not be excluded because they represent a signi ficant portion of the lightduty fleet, while CARB and ICCT stated that because DRI found safety benefits whether 2-door cars were included or not, NHTSA s hould include 2-door cars in its analysis.

Wenzel also commented that NHTSA should in clude 2-door cars in s ubsequent analyses, stating that while his analysis of MY 2000-2004 crash data from 5 states indicates that, in general, 4-door cars tend to ha ve lower fatality risk than 2- door cars, the risk is even

lower when he accounts for driv er age/gender and cr ash location. Wenzel suggested that

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the increased fatality risk in the 2-door car population seemed primar ily attributable to the sports cars, and that that was not suffi cient grounds to exclude all 2-door cars from NHTSA’s analysis.

Agencies’ response:

The agencies agree that 2-door cars can be included in the analysis, and NHTSA retracts previous statements that DRI’s in clusion of them was incorrect. In its 2010 analysis, NHTSA finds that it makes little difference to the results whether 2-door cars are included, partially included, or excluded from the analysis. Thus, analyses of 2-door and 4-door cars combined, as well as other combinations, have been included in the analysis. That said, no comb ination of 2-door and 4-door cars resulted in NHTSA’s finding a safety benefit for pa ssenger cars due to mass reduction.

NHTSA and DRI may have reached differe nt conclusions due to different assumptions

DRI commented that the differences found between its study and NHTSA’s may be due to the different assumptions about th e linearity of the curb weight effect and control variable for driver age, vehicle age, road conditions, and ot her factors. NHTSA’s analysis was based on a two-piece linear model fo r curb weight with two different weight groups (less than 2,950 lbs., and greater than or equal to 2.950 lbs). The DRI analysis assumed a linear model for curb weight with a single weight group. Additionally, DRI stated that NHTSA’s use of eight control va riables (rather than three control variables like DRI used) for driver age introduces additional degrees of freedom into the regressions, which it suggested may be correl ated with the curb weight, wheelbase, and track width, and/or other contro l variables. DRI suggested that this may also affect the

results and cause or contribute to the diffe rences in outcomes between NHTSA and DRI.

Agencies’ response:

NHTSA’s FRIA documents that NHTSA anal yzed its database using both a single parameter for weight (a linear model) and tw o parameters for weight (a two-piece linear model). In both cases, the l ogistic regression responded iden tically, alloca ting the same way between weight, wheelbase , track width, or footprint. 23 Thus, NHTSA does not

believe that the differences be tween its results and DRI’s re sults are due to whether the studies used a single weight group or two weight groups.

The FRIA also documents that NHTSA ex amined NHTSA’s use of eight control variables for driver age (age s 14-30, 30-50, 50-70, 70+ for male s and females separately ,

versus DRI’s use of three cont rol variables for age (FEMALE = 1 for females, 0 for males, YOUNGDRV = 35-AGE for drivers under 35, 0 for all others, OLDMAN = AGE-50 for males over 50, 0 for all others; OLDWOMAN = AGE-45 for females over 45, 0 for all others) to see if that affected the results. NHTSA ran its analysis using the eight control variables and ag ain using three control vari ables for age, and obtained

23 Sections 2.2 and 2.3 of new report

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similar results each time. 24 Thus, NHTSA does not believe that the differences between

its results and DRI’s results are due to the number of control variab les used for driver

age.

NHTSA’s and DRI’s conclusions may be similar if confidence intervals are

taken into account

DRI commented that NHTSA has not reported confidence intervals, while DRI has reported them in its studies. Thus, DRI argued, it is not po ssible to determine whether the confidence intervals overlap a nd whether the differences between NHTSA’s and DRI’s analyses are statistically significant.

Agencies’ response:

NHTSA has included confidence interval s for the main results of the 2010 Kahane analysis, as shown in Chapter IX of NHTSA’s FRIA. For passenger cars, the NHTSA results are a statistically signifi cant increase in fata lities with a 100 pound reduction while maintaining track width and wh eelbase (or footprint); the DRI results are a statistically significant decrease in fatalities with a 100 pound reduction while maintaining track width and wheelbase. The DRI results are thus outside the confidence bounds of the NHTSA results and do not overlap.

NHTSA should include a “best-c ase” estimate in its study

Several commenters (Center for Auto Sa fety, NRDC, Public Citizen, Sierra Club

et al. , and Wenzel) urged NHTSA to include a “best-case” estimate in the final rule, showing scenarios in which lives were saved rath er than lost. Public Citizen stated that there would be safety benefits to reducing the weight of the heaviest vehicles while leaving the weight of the lig hter vehicles unchanged, and that increasing the number of smaller vehicles would provide safety be nefits to pedestrians, bicyclists, and motorcyclists. Sierra Club et al . stated that new materials, smart design, and lighter, more advanced engines can all improve fuel economy while maintaining or increasing vehicle safety. Both Center for Auto Safe ty and Sierra Club argued that the agency should have presented a “best-case” scenario to balance out the “worst-case” scenario presented in the NPRM, especially if NHTSA itself believed that the worst-case scenario was not inevitable. NRDC requested that NHTSA present both a “best-case” and a “most likely” scenario. Wenzel simply stated that NHTSA did not present a “best-case” scenario, despite DRI’s finding in 2005 that fatalities would be reduced if track width

was held constant.

Agencies’ response:

NHTSA has included an “uppe r estimate” and a “lower estimate” in the new 2010 Kahane analysis. The lower estimate assumes that mass reduction will be accomplished entirely by material substitution or other techniques that do not perceptibly change a

24 Id.

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vehicle’s shape, structural st rength, or ride quality. The lower estimate examines specific

crash modes and is meant to reflect the increas e in fatalities for the specific crash modes

in which a reduction in mass per se in the case vehicle would result in a reduction in safety: namely, collisions with larger vehicles not covered by the regulations ( e.g. , trucks with a GVWR over 10,000 lbs), collisions with partially-movable objects ( e.g. , some trees, poles, parked cars, etc.), and collisions of cars or light LTVs with heavier LTVs – as well as the specific crash modes where a reduction in mass per se in the case vehicle would benefit safety: namely, collisions of heavy LTVs with cars or lighter LTVs.

NHTSA believes that this is the effect of mass per se , i.e. , the effects of reduced mass will generally persist in these crashes regardless of how the mass is reduced. The lower estimate attempts to quantify that scenario, although any such estimate is hypothetical and subject to considerable uncertainty. NHT SA believes that a “most likely” scenario cannot be determined with any certain ty, and would depend entirely upon agency assumptions about how manufacturers intend to reduce mass in their vehicles. While we can speculate upon the potential effects of different methods of mass reduction, we cannot predict with certainty what manufacturers will ultimately do.

NHTSA should not include a “wo rst-case” estimate in its study

NRDC, Public Citizen and Sierra Club et al. commented that NHTSA should

remove the “worst-case scenar io” estimate from the rulema king, generally because it was based on an analysis that evaluated histori cal vehicles, and future vehicles would be sufficiently different to render the “worst-case scenario” inapplicable.

Agencies’ response:

NHTSA stated in the NPRM that the “worst -case scenario” addre ssed the effect of a kind of downsizing ( i.e. , mass reduction accompanied by f ootprint reduction) that was not likely to be a consequence of attribute-based CAFE sta ndards, and that the agency would refine its analys is of such a scenario for the fi nal rule. NHTSA has not used the

“worst-case scenario” in the fina l rule. Instead, we present thr ee scenarios: the first is an estimate based directly on the regres sion coefficients of weight reduction while maintaining footprint in the statistical analyses of hi storical data. As discussed above, presenting this scenario is possible because NHTSA was able to separate the effects of weight and footprint reduction in the new anal ysis. However, even the new analysis of LTVs produced some coefficients that NHTSA did not consider entirely plausible. NHTSA also presents an “upper estimate” in which those coefficients for the LTVs were adjusted based on additional analyses and expe rt opinion as a safety agency and a “lower estimate,” which estimates the effect if mass reduction is accomplished entirely by safety-conscious technologies such as material substitution.

3. How has NHTSA refined its analysis for purposes of estimating the potential safety effects of this final rule?

During the past months, NHTSA has exte nsively reviewed the literature on vehicle mass, size, and fatality risk. NHTSA now agrees with DRI and other commenters

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that it is essential to analyze the effect of mass independently from the effects of size parameters such as wheelbase, track width, or footprint – and that the NPRM’s “worstcase” scenario based on downsizing (in which weight, wheelbase, and track width could all be changed) is not useful for that purpose. The agency should instead provide estimates that better reflect the more likely e ffect of the regulation - estimating the effect

of mass reduction that maintains footprint.

Yet it is more difficult to analyze multiple, independent parameters than a single parameter ( e.g. , curb weight), because there is a potential concern that the near multicollinearity of the paramete rs – the strong, natural and historical correlation of mass

and size – can lead to inaccurate stat istical estimates of their effects. 25 NHTSA has performed new statistical analyses of its hi storical database of passenger cars, light trucks, and vans (LTVs) from its 2003 report (now including also 2-door cars), assessing relationships between fatality risk, mass, and footprint. They are described in Sections 2.2 (cars) and 3.2 (LTVs) of the 2010 Kahane report presented in Chapter IX of the FRIA. While the potential conc erns associated with near mu lticollinearity are inherent in regression analyses with multiple size/mass parameters, NHTSA believes that the analysis approach in the 2010 Kahane report, namely a single-step regression analysis, generally minimizes those hazards 26 and models the trends in the historical data. The results differ substantially from DRI’s, based on a two-step regression analysis. Sections 2.3 and 2.4 of the 2010 Kahane report attempt to account for the differences primarily by applying selected techniques from DRI’s analyses to NHTSA’s database.

The statistical analyses – logistic regressions – of trends in MYs 1991-1999 vehicles generate one set of estimates of the possible effects of reducing mass by 100 pounds while maintaining footprint. While thes e effects might concei vably carry over to future mass reductions, there are two reasons th at future safety effects of mass reduction could differ from projections from historical data:

• The statistical analyses are “cross-sectional” analyses that estimate the increase in fatality rates for vehicles weighing n- 100 pounds relative to vehicles weighing n pounds, across the spectrum of vehicles on the road, from th e lightest to the heaviest. They do not directly compare the fatality rates for a specific make and model before and after a 100–pound reduction fro m that model. Instead, they use

the differences across makes and models as a surrogate for the effects of actual reductions within a specific model; those cross-sectional differences could include

trends that are statis tically, but not causally related to mass.

25 Greene, W. H. (1993). Econometric Analysis , Second Edition. New York: Macmillan Publishing Company, pp. 266-268; Allison, P.D. (1999), Logistic Regression Using the SAS System . Cary, NC: SAS Institute Inc., pp. 48-51. The report shows variance in flation factor (VIF) scores in the 5-7 range for curb weight, wheelbase, and track width (or, alternatively, curb weight and footprint) in NHTSA’s database, exceeding the 2.5 level where near mu lticollinearity begins to become a concern in logistic regression analyses.

26 NHTSA believes that the two-step regression is more hazardous because it weakens relationships between curb weight and dependent variables by splitting the effect of curb weight across the two regression steps, as disc ussed further below.

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• The manner in which mass changed across MY 1991-1999 vehicles might not be consistent with future mass reductions, due to the availability of newer materials and design methods.

Therefore, Sections 2.5 and 3.4 of the 2010 Kahane report supplement those estimates

with one or more scenarios in which some of the logistic regression coefficients are replaced by numbers based on additional anal yses and NHTSA’s judgment of the likely

effect of mass per se (the ability to transfer momentum to other vehicles or objects in a collision) and of what trends in the hist orical data could be avoided by current massreduction technologies such as materials su bstitution. The various scenarios may be viewed as a plausible range of point estimates for the e ffects of mass reduction while maintaining footprint, but they should not be construed as upper and lower bounds. Furthermore, being point estimates, they are th emselves subject to uncertainties, such as, for example, the sampling errors associated with statistical analyses.

The principal findings and conclusions of the 2010 Kahane report are as follows:

Passenger cars : This database with the one-ste p regression method of the 2003 Kahane report estimates an increase of 700-800 fata lities when curb weight is reduced by 100 pounds and footprint is reduced by 0.65 square fe et (the historic average footprint reduction per 100-pound mass reduction in cars). The regression attributes the fatality increase about equally to curb weight and to footprint . The results are approximately the same whether 2-door cars are fully included or partially included in the analysis or whether only 4-door cars are included (as in the 2003 report). Regressions by curb weight, track width and wheel base produce findings quite similar to the regressions by curb weight and footprint, but the results with the single “size” variable, footprint, rather than the two variables, track width and wheel base vary even less w ith the inclusion or

exclusion of 2-door cars.

In Section 2.3 of the new report, a tw o-step regression method that resembles (without exactly replicating) the approach by DRI, when applied to the same (NHTSA’s) crash and registration data , estimates a large benefit when mass is reduced, offset by even larger fatality increases when track width and wheelbase (or footprint) are reduced.

NHTSA believes that the benefit estimated by this method is inaccurate, due to the potential concerns with the near multicollin earity of the parameters (curb weight, track width, and wheelbase) 27 even though the analysis is theoretically unbiased 28 . Almost any analysis incorporating those parameters has a possibility of inaccurate coefficients due to near multicollinearity; however, based on our own experience with other regression analyses of crash data, NHTSA believes a DRI-type two-step method augments the possibility of estimating inaccurate coeffici ents for curb weight, because it weakens

27 As evidenced by VIF scores in the 5-7 range, excee ding the 2.5 level where near multicollinearity begins to become a concern in logi stic regression analyses.

28 Section 2.3 of the 2010 Kahane report attempts to explain why the two-step method, when applied to NHTSA’s 2003 database, produces results a lot like DRI’s, but it does not claim that DRI obtained its results from its own database for exactly those reason s. NHTSA did not analyze DRI’s database. The twostep method is “theoretically unbiased” in the sense that it seeks to estimate the same parameters as the one-step analysis.

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relationships between curb weight and depende nt variables by splitting the effect of curb weight across the two regression steps.

In Section 2.4 of the new report, as a check on the results from the regression methods, NHTSA also performed what we refer to as “decile” analys es: simpler, tabular data analysis that compares fatality rates of cars of different mass but similar footprint. Decile analysis is not a precise tool because it does not control for confounding factors such as driver age/gender or th e specific type of car, but it may be helpful in identifying the general directional trend in the data when footprint is held constant and curb weight varies. The decile analyses show that fatality risk in MY 1991-1999 cars generally increased and rarely decreased for lighter rela tive to heavier cars of the same footprint

. They suggest that the historical, cross-s ectional trend was gene rally in the lighter ↔ more fatalities direction and not in the opposite direction, as might be suggested by the regression coefficients from the met hod that resembles DRI’s approach.

The regression coefficients from NHTS A’s one-step method suggest that mass and footprint each accounted for about half the fatality increase associated with downsizing in a cross-sectiona l analysis of 1991-1999 cars. They estimate the historical

difference in societal fatality rates ( i.e. , including fatalities to o ccupants of all the vehicles involved in the collisions, plus any pedestrian s) of cars of different curb weights but the same footprint. They may be considered an “upper-estimate scenario ” of the effect of future mass reduction – if it were accomplished in a manner that resembled the historical

cross-sectional trend – i.e. , without any particular regard for safety (other than not to reduce footprint).

However, NHTSA believes that future vehi cle design is likely to take advantage of safety-conscious technologies such as materials substitution that can reduce mass without perceptibly chan ging a car’s shape or ride and main tain its structural strength.

This could avoid much of the risk associated with lighter and sma ller vehicles in the historical analyses, especially the historical trend toward higher crash-involvement rates for lighter and smaller vehicles. 29 It could thereby shrink the added risk close to just the

effects of mass per se (the ability to transfer momentum to other vehicles or objects in a collision). Section 2.5 of the 2010 Kahane repo rt attempts to quan tify a “lower-estimate scenario” for the potential effect of mass reduction achieved by safety-conscious technologies; the estimated effects are substa ntially smaller than in the upper-estimate scenario based directly on the regression results.

We note, again, that the preceding paragra ph is conditional. Nothing in the CAFE standard requires manufacturers to use mate rial substitution or, more generally, take a safety-conscious approach to mass reduction. 30 Federal Motor Vehicle Safety Standards include performance tests that verify historic al improvements in stru ctural strength and

29 IIHS Advisory No. 5, July 1988, http://www.iih s.org/research/advisories/iih s_advisory_5.pdf; IIHS News Release, February 24, 1998, http://www.iih s.org/news/1998/iihs_news_02 2498.pdf; Auto Insurance Loss Facts, September 2009, h ttp://www.iihs.org/res earch/hldi/fact_sheets/CollisionLoss_0909.pdf.

30 Footprint-based standards do not specify how or where to remove mass while maintaining footprint, nor do they categorically forbid footprint re ductions, even if they discourage them.

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crashworthiness, but few FMV SS provide test information th at sheds light about how a vehicle rides or otherwise helps explain the trend toward higher crash-involvement rates for lighter and smaller vehicles. It is possi ble that using material substitution and other

current mass reduction methods could avoid the historical trend in this area, but that

remains to be studied as manufacturers introdu ce more of these vehicles into the on-road fleet in coming years.

LTVs : The principal difference between LTVs a nd passenger cars is that mass reduction in the heavier LTVs is estimated to have signific ant societal benefits, in that it reduces the fatality risk for the occupants of cars and lig ht LTVs that collide with the heavier LTVs. By contrast, footprint (size) reduction in LTVs has a harmful effect (for the LTVs’ own occupants), as in cars. The regression method of the 2003 Kahane re port applied to the database of that report estimat es a societal increase of 231 fa talities when curb weight is reduced by 100 pounds and footprint is reduced by 0.975 square feet (the hi storic average footprint reduction per 100- pound mass reduction in LTVs). But the regressions attribute

an overall reduction of 266 fatalities to the 100-pound mass reducti on and an increase of 497 fatalities to the .975-square -foot footprint reduction. The regression results constitute

one of the scenarios for the possible societal effects of future mass reduction in LTVs.

However, NHTSA cautions that some of the regression coefficients, even by NHTSA’s preferred method, might not accurately model the historical trend in the data, possibly due to near multicollin earity of curb weight and footprint or because of the

interaction of both of thes e variables with LTV type. 31 Based on supplementary analysesand discussion in Sections 3.3 and 3.4, the new report defines an additional upperestimate scenario that NHTSA believes may more accurately reflect the historical trend in

the data and a lower-estimate scenario that may come closer to the effects of mass per se

. All three scenarios, however, attribute a soci etal fatality reduction to mass reduction in

the heavier LTVs.

Overall effects of mass reduction while maintaining footprint in cars and LTVs : The immediate purpose of the new report’s analyses of relationships between fatality risk, mass, and footprint is to deve lop the four parameters that the Volpe model needs in order to predict the safety effect s, if any, of the modeled mass reductions in MYs 2012-2016

cars and LTVs over the lifetime of those ve hicles. The four numbers are the overall percentage increases or decreases, per 100-pound mass reduction wh ile holding footprint constant, in crash fatalities involving: (1 ) cars < 2,950 pounds (which was the median curb weight of cars in MY 1991-1999), (2) cars ≥ 2,950 pounds, (3) LTVs < 3,870 pounds (which was the median curb weight of LTVs in those model years), and (4) LTVs

≥ 3,870 pounds. Here are the percentage eff ects for each of the three alternative scenarios, again, the “upper-estimate scenario ” and the “lower-estimate scenario” have been developed based on NHTSA’s expert opinion as a vehicle safety agency:

31 For example, mid-size SUVs of the 1990s typically had high mass relative to their short wheelbase and footprint (and exceptionally high rates of fatal rollovers); minivans typically have low mass relative to their footprint (and low fatality rates); heavy-duty pickup trucks used extensively for work tend to have more mass, for the same footprint, as basic full-sized pi ckup trucks that are more often used for personal transportation.

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Fatality Increase per 100-Pound Reduction (%)

Actual Regression

Result Scenario NHTSA ExpertOpinion UpperEstimate

Scenario 32 NHTSA ExpertOpinion LowerEstimate Scenario

Cars < 2,950 pounds 2.21 2.21 1.02

Cars > 2,950 pounds 0.90 0.90 0.44

LTVs < 3,870 pounds 0.17 0.55 0.41

LTVs > 3,870 pounds -1.90 -0.62 -0.73

In all three scenarios, the estimated effects of a 100-pound mass reduction while maintaining footprint are an increase in fa talities in cars < 2,950 pounds, substantially

smaller increases in cars ≥ 2,950 pounds and LTVs < 3,870 pounds, and a societal benefit

for LTVs ≥ 3,870 pounds (because it reduces fatality risk to occupants of cars and lighter LTVs they collide with). These are the es timated effects of reducing each vehicle by exactly 100 pounds. However, the actual mass reduction will vary by make, model, and year. The aggregate effect on fatalities can only be estimated by attempting to forecast, as NHTSA has using inputs to the Volpe model, the mass reduc tions by make and model. It should be noted, however, that a 100-pound reduction would be 5 percent of the mass of a 2000-pound car but only 2 percent of a 5000-pound LTV. Thus, a forecast that mass will decrease by an equal or greater percentage in the heavier vehicles than in the lightest cars would be proportionately more influenced by the benefit for mass reduction in the heavy LTVs than by the fatality increases in th e other groups; it is lik ely to result in an

estimated net benefit under one or more of the scenarios. It should also be noted, again, that the three scenarios are point estimates a nd are subject to uncertainties, such as the sampling errors associated with the regressi on results. In the scenario based on actual regression results, the 1.96-sigma sampling errors in the above estimates are + 0.91 percentage points for cars < 2,950 pounds and also for cars > 2,950 pounds, + 0.82 percentage points for LTVs < 3,870 pounds, and + 1.18 percentage points for LTVs > 3,870 pounds. In other words, the fatality in crease in the cars < 2,950 pounds and the societal fatality reduction attri buted to mass reduc tion in the LTVs > 3,870 pounds are statistically significant. The sampling errors associated with the scenario based on actual regression results perhaps also indicate the general level of statistical noise in the other

two scenarios.

4. What are the estimated safety effects of this final rule?

32 For passenger cars, the up per-estimate scenario is the actual-regression-result scenario.

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The table below shows the estimated safety effects of the modeled reduction in vehicle mass provided in the NPRM and in this final rule in order to meet the MYs 2012- 2016 standards, based on the analysis describe d briefly above and in much more detail in Chapter IX of the FRIA. Thes e are combined results for pass enger cars and light trucks. A positive number is an estimated increase in fatalities and a negative number (shown in parentheses) is an estimated reduction in fa talities over the lifetime of the model year vehicles compared to the MY 2011 baseline fleet.

MY

2012 MY

2013 MY

2014 MY

2015 MY

2016

NPRM “Worst Case” 34 54 194 313 493

NHTSA Expert Opinion Final Rule Upper Estimate 9 14 26 24 22

NHTSA Expert Opinion Final Rule

Lower Estimate 2 4 (17) (53) (80)

Actual Regression

Result Scenario 0 2 (94) (206) (301)

NHTSA emphasizes that the table above is based on the NHTSA’s assumptions about how manufacturers might choose to reduce the mass of their vehicles in response to the final rule, which are very similar to EP A’s assumptions. In general, as discussed above, the agencies assume that mass will be reduced by as much as 10 percent in the heaviest LTVs but only by as much as 5 percen t in other vehicles and that substantial mass reductions will take place only in the year that models are redesigned. The actual mass reduction that is likely to occur in res ponse to the standards will of course vary by make and model, depending on each manufact urer’s particular approach, with likely more opportunity for the largest LTVs that still use separate frame construction.

The “upper estimate” presented above, as discussed in the FRIA, assumes only that manufacturers will reduce vehicle mass without reducing footprint. Thus, under such a scenario, safety effects could be somewh at adverse if, for example, manufacturers chose to reduce crush space associated with vehicle overhang as a way of reducing mass without changing footprint. The “lower es timate,” in turn, is based on the assumption

that manufacturers will reduce vehicle ma ss solely through methods like material substitution, which (under th ese assumptions) fully maintain not only footprint but also all structural integrity, and othe r aspects of vehicle safety. Under these scenarios, safety

effects could be worse if mass reduction wa s not undertaken thoughtfully to maintain existing safety levels, but could also be be tter if it was undertak en with a thorough and extensive vehicle redesign to maxi mize both mass reduction and safety.

And finally, while NHTSA does not belie ve that the “worst-case” scenario presented in the NPRM is likely to occur during the MYs 2012-2016 timeframe, we cannot guarantee that manufacturers will neve r choose to reduce vehicle footprint, particularly if market forces lead to increased sales of sma ll vehicles in response to sharp

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increases in the price of petroleum, though this situation would not be in direct response to the CAFE/GHG standards. Thus, we cannot completely reject th e worst-case scenario for all vehicles, although we can and do recogni ze that the footprin t-based standards will significantly limit the likelihood of its occurrence within the context of this rulemaking.

In summary, the agencies recognize the balancing inherent in achieving higher levels of fuel economy and lower levels of CO 2 emissions through reduction of vehicle mass. Based on the 2010 Kahane analysis that is able to separate the effects of mass reductions and footprint reductions, and to acc ount better for the possibility that mass reduction will be accomplished entirely th rough methods that pr eserves structural strength and vehicle safety, the agencies now believe that the likely deleterious safety effects of the MYs 2012-2016 standards may be much lower than originally estimated. They may be close to zero, or possibly beneficial if mass reduction is carefully

undertaken in the future and if the mass re duction in the heavier LTVs is greater (in absolute terms) than in passenger cars. In light of these findings, we believe that the balancing is reasonable.

5. How do the agencies plan to address this issue going forward?

NHTSA and EPA believe that it is importa nt for the agencies to conduct further study and research into the in teraction of mass, size and safety to assist future rulemakings. The agencies intend to begin working collaboratively and to explore with DOE, CARB, and perhaps other stakeholders an interagency/ intergovernmental working group to evaluate all aspects of mass, size and safety. It would also be the goal of this team to coordinate government supported studies and independent research, to the extent possible, to help ensure the work is comp lementary to previous and ongoing research and to guide further research in this area. DOE’s EERE office has long funded extensive research into component advanced vehicle materials and vehicle mass reduction. Other agencies may have additional expertise that will be helpful in establishing a coordinated work plan. The agencies are interested in looking at the weight-s afety relationship in a more holistic (complete vehicl e) way, and thanks to this CAFE rulemaking NHTSA has begun to bring together parts of the agen cy— crashworthiness, and crash avoidance rulemaking offices and the agency’s Re search & Development office—in an interdisciplinary way to better leverage the expe rtise of the agency. Extending this effort to other agencies will help to ensure that a ll aspects of the weight -safety relationship are considered completely and carefully with our fu ture research. The agencies also intend to carefully consider comments received in res ponse to the NPRM in developing plans for

future studies and research and to solicit input from stakeholders.

The agencies also plan to watch for safety effects as the U.S. light-duty vehicle fleet evolves in response both to the CAFE/GHG standards a nd to consumer preferences over the next several years. Additionally, as new and advanced ma terials and component smart designs are developed and commercialized, and as manufacturers implement them in more vehicles, it will be useful for the agen cies to learn more about them and to try to

track these vehicles in the fleet to unders tand the relationship betw een vehicle design and

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injury/fatality data. Sp ecifically, the agencies intend to follow up with study and research of the following:

First, NHTSA is in the process of contra cting with an independent institution to

review the statistical methods that NHTSA has used to analy ze historical data related to mass, size and safety, and to provide recomm endation on whether the existing methods or

other methods should be used for future statisti cal analysis of historic al data. This study is being initiated because, in response to the NPRM, NHTSA received a number of comments related to the methodology NHTSA used for the NPRM to determine the relationship between mass and safety, as discussed in detail above.

Second, NHTSA and EPA, in consultati on with DOE, intend to begin updating the MYs 1991-1999 database on which the safety analyses in the NPRM and final rule

are based with newer vehicle data in the next several months. This task will take at least a year to complete. This study is being initiated in response to the NPRM comments

related to the use of data from MYs 1991-1999 in the NHTSA analysis, as discussed in

detail above.

Third, in order to assess if the design of recent model year vehicles that incorporate various mass reduction methods aff ect the relationships among vehicle mass, size and safety, NHTSA and EPA intend to c onduct collaborative statistical analysis, beginning in the next several months. The agen cies intend to work with DOE to identify vehicles that are using material substituti on and smart design. After these vehicles are identified, the agencies intend to assess if ther e are sufficient data for statistical analysis. If there are sufficient data, statistical an alysis would be cond ucted to compare the relationship among mass, size and safety of thes e smart design vehicles to vehicles of similar size and mass with more traditional design s. This study is being initiated because, in response to the NPRM, NHTSA received co mments related to the use of data from MYs 1991-1999 in the NHTSA analysis that di d not include new designs that might change the relationship among mass, size and safety, as discusse d in detail above.

NHTSA may initiate a two-year study of the safety of the fleet through an analysis of the trends in st ructural stiffness and whether any trends identified impact occupant injury response in crashes. Vehicle manufactur ers may employ stiffer light weight materials to limit occupant compartment intrusion while controlling for mass that may expose the occupants to higher accelerations resulting in a grea ter chance of injury in real-world crashes. This study would provide information that would increase the understanding of the effects on safety of newer vehicle designs.

In addition, NHTSA and EPA, possibly in collaboration with DOE, may conduct a longer-term computer modeling-based design and analysis study to help determine the maximum potential for mass reduction in the MYs 2017-2021 timeframe, through direct material substitution and smart design while meeting safety regulations and guidelines, and maintaining vehicle size and functionalit y. This study may build upon prior research completed on vehicle mass reduction. This study would further explore the comprehensive vehicle effects, including dissimilar material joining technologies,

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manufacturer feasibility of both supplier and OEM, tooling costs, and crash simulation and perhaps eventual crash testing.

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