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Chapter 9. Safety Impacts

9.1 Summary of Supporting HD Vehicle Safety Research

NHTSA and EPA considered the potential safety impact of technologies that improve HD 

vehicle fuel efficiency and GHG emissions as part of the assessment of regulatory alternatives. 

The safety assessment of the technologies in this proposal was informed by two NAS reports, an 

analysis of safety effects of HD pickups and vans using estimates from the DOT report on the 

effect of mass reduction and vehicle size on safety, and agency-sponsored safety testing and 

research. A summary of the literature and work considered by the agencies follows. 

9.2 National Academy of Sciences HD Phase 1 and Phase 2 Reports

As required by EISA, the National Research Council has conducted two studies of the 

technologies and approaches for reducing the fuel consumption of medium- and heavy-duty 

vehicles. The first was documented in a report issued in 2010, “Technologies and Approaches to 

Reducing the Fuel Consumption of Medium- and Heavy-Duty Vehicles’’ (“NAS Report”).A The 

second was documented in a report issued in 2014, “Reducing the Fuel Consumption and 

Greenhouse Gas Emissions of Medium- and Heavy-Duty Vehicles, Phase Two-First Report” 

(“NAS HD Phase 2 First Report”).B While the reports primarily focused on reducing vehicle 

fuel consumption and emissions through technology application, and examined potential 

regulatory frameworks, both reports additionally contain findings and recommendations on 

safety. In developing this proposal, the agencies carefully considered both of the reports’ 

findings related to safety. Some of the reports’ key findings related to safety follow.

NAS commented that idle reduction strategies can be sophisticated to provide for the 

safety of the driver in hot and cold weather. The agencies considered this comment in our 

approach for idle reduction technologies (e.g., APUs, diesel fired heaters, and battery powered 

units with automatic engine shutoff (AES)) and allow override provisions, as discussed in 

Preamble Section III. Override of the automatic engine shutoff (AES) feature is allowed if the 

external ambient temperature reaches a level below which or above which the cabin temperature 

cannot be maintained within reasonable heat or cold exposure threshold limit values for the 

health and safety of the operator (not merely comfort).

 

A Committee to Assess Fuel Economy Technologies for Medium- and Heavy-Duty Vehicles; National Research 

Council; Transportation Research Board (2010). “Technologies and Approaches to Reducing the Fuel Consumption 

of Medium- and Heavy-Duty Vehicles.” Washington, D.C., The National Academies Press. Available electronically 

from the National Academy Press Website at http://www.nap.edu/catalog/12845/technologies-and-approaches-toreducing-the-fuel-consumption-of-medium--and-heavy-duty-vehicles (last accessed June 4, 2015).

B Transportation Research Board 2014. “Reducing the Fuel Consumption and Greenhouse Gas Emissions of

Medium- and Heavy-Duty Vehicles, Phase Two.” Washington, D.C., The National Academies Press. Available 

electronically from the National Academy Press Website http://www.nap.edu/catalog/18736/reducing-the-fuelconsumption-and-greenhouse-gas-emissions-of-medium--and-heavy-duty-vehicles-phase-two (last accessed June 4, 

2015).
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NAS commented extensively on the recent emergence of natural gas (NG) as a viable 

technology option for commercial vehicles, but alluded to the existence of uncertainties 

regarding its safety. The committee found that while the public crash databases do not contain 

information on vehicle fuel type, the existing information indicates that the crash-related safety 

risk for NG storage on vehicles does not appear to be appreciably different from diesel fuel risks. 

The committee also found that while there are two existing SAE-recommended practice 

standards for NG-powered HD vehicles, the industry could benefit from best practice directives 

to minimize crash risks for NG fuel tanks, such as on shielding to prevent punctures during 

crashes. As a final point, NAS stated that manufacturers and operators have a great incentive to 

prevent possible NG leakage from a vehicle fuel system because it would be a significant safety 

concern and reduce vehicle range. No recommendations were made for additional Federal safety 

regulations for these vehicles. In response, the agencies have reviewed and discuss the existing 

NG vehicle standards and best practices cited by NAS in Section XI.

In the NAS Committee’s Phase 1 report, the Committee commented that aerodynamic 

fairings detaching from trucks on the road was a potential safety issue. However, the Phase 2 

interim report stated that “Anecdotal information gained during the observations of on-road 

trailers indicates a few skirts badly damaged or missing from one side. The skirt manufacturers 

report no safety concerns (such as side skirts falling off) and little maintenance needed.” 

The NAS report also identified the link between tire inflation and condition and vehicle 

stopping distance and handling, which impacts overall safety. The committee found that tire 

pressure monitoring systems and automatic tire inflation systems are being adopted by fleets at 

an increasing rate. However, the committee noted that there are no standards for performance, 

display, and system validation. The committee recommended that NHTSA issue a white paper 

on the minimum performance of tire pressure systems from a safety perspective. 

The agencies considered the safety findings in both NAS reports in developing this 

proposal and conducted additional research on safety to further examine information and 

findings of the reports.

9.3 DOT CAFE Model HD Pickup and Van Safety Analysis

This analysis considered the potential effects on crash safety of the technologies 

manufacturers may apply to their HD pickups and vans to meet each of the regulatory

alternatives evaluated. NHTSA research has shown that vehicle mass reduction affects overall 

societal fatalities associated with crashes and, most relevant to this proposal, that mass reduction 

in heavier light- and medium-duty vehicles has an overall beneficial effect on societal fatalities. 

Reducing the mass of a heavier vehicle involved in a crash with another vehicle(s) makes it less 

likely that there will be fatalities among the occupants of the other vehicles. In addition to the 

effects of mass reduction, the analysis anticipates that the proposed standards, by reducing the 

cost of driving HD pickups and vans, would lead to increased travel by these vehicles and, 

therefore, more crashes involving these vehicles. The Method A analysis considers overall 

impacts from both of these factors, using a methodology similar to NHTSA’s analyses for the 

MYs 2017 – 2025 CAFE and GHG emission standards.
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The Method A analysis includes estimates of the extent to which HD pickups and vans

produced during MYs 2014-2030 may be involved in fatal crashes, considering the mass, 

survival, and mileage accumulation of these vehicles, taking into account changes in mass and 

mileage accumulation under each regulatory alternative. These calculations make use of the 

same coefficients applied to light trucks in the MYs 2017-2025 CAFE rulemaking analysis. As 

discussed above, vehicle miles traveled may increase due to the fuel economy rebound effect, 

resulting from improvements in vehicle fuel efficiency and cost of fuel, as well as the assumed 

future growth in average vehicle use. Increases in total lifetime mileage increase exposure to 

vehicle crashes, including those that result in fatalities. Consequently, the modeling system 

computes total fatalities attributed to vehicle use for vehicles of a given model year based on 

safety class and weight threshold. These calculations also include a term that accounts for the 

fact that vehicles involved in future crashes will be certified to more stringent safety standards 

than those involved with past crashes upon which the base rates of involvement in fatal crashes 

were estimated. Since the use of mass reducing technology is present within the model, safety 

impacts may also be observed whenever a vehicle’s base weight decreases. Thus, in addition to 

computing total fatalities related to vehicle use, the modeling system also estimates changes in 

fatalities due to reduction in a vehicle’s curb weight. 

The total fatalities attributed to vehicle use and vehicle weight change for vehicles of a 

given model year are then summed. Lastly, total fatalities occurring within the industry in a 

given model year are accumulated across all vehicles. In addition to using inputs to estimate the 

future involvement of modeled vehicles in crashes involving fatalities, the model also applies 

inputs defining other accident-related externalities estimated on a dollar per mile basis. For 

vehicles above 4,594 pounds—i.e., the majority of the HD pickup and van fleet—mass reduction 

is estimated to reduce the net incidence of highway fatalities by 0.34 percent per 100 pounds of 

removed curb weight. For the few HD pickups and vans below 4,594 pounds, mass reduction is 

estimated to increase the net incidence of highway fatalities by 0.52 percent per 100 pounds. 

Because there are many more HD pickups and vans above 4,594 pounds than below 4,594 

pounds, the overall effect of mass reduction in the segment is estimated to reduce the incidence 

of highway fatalities. The estimated increase in vehicle miles traveled due to the fuel economy 

rebound effect is estimated to increase exposure to vehicle crashes and offset these reductions. 

9.4 Volpe Research on MD/HD Fuel Efficiency Technologies

The 2010 NAS Report recommended that NHTSA perform a thorough safety analysis to 

identify and evaluate potential safety issues with fuel efficiency-improving technologies. The 

Department of Transportation Volpe Center’s 2015 report titled “Review and Analysis of 

Potential Safety Impacts of and Regulatory Barriers to Fuel Efficiency Technologies and 

Alternative Fuels in Medium- and Heavy-Duty Vehicles” Csummarizes research and analysis 

findings on potential safety issues associated with both the diverse alternative fuels (natural gas-

 

C Brecher, A., Epstein, A. K., & Breck, A. (2015, June). “Review and analysis of potential safety impacts of and 

regulatory barriers to fuel efficiency technologies and alternative fuels in medium- and heavy-duty vehicles.”

(Report No. DOT HS 812 159). Washington, DC: National Highway Traffic Safety Administration.
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CNG and LNG, propane, biodiesel, and power train electrification), and the specific FE 

technologies recently adopted by the MD/HDV fleets. These include Intelligent Transportation 

Systems (ITS) and telematics, speed limiters, idle reduction devices, tire technologies (singlewide tires, and tire pressure monitoring systems-TPMS and Automated Tire Inflation SystemsATIS), aerodynamic components, vehicle light-weighting materials, and Long Combination 

Vehicles (LCVs). 

Chapter 1 provides an overview of the study’s rationale, background, and key objective, 

namely, to identify the technical and operational/behavioral safety benefits and disbenefits of 

MD/HDVs equipped with FE technologies and using emerging alternative fuels (AFs). Recent 

MD/HDV national fleet crash safety statistical averages are also provided for context, although 

no information exists in crash reports relating to specific vehicle FE technologies and fuels.

(NHTSA/FARS and FMCSA/CSA databases do not include detailed information on vehicle fuel 

economy technologies, since the state crash report forms are not coded down to an individual 

fuel economy technology level).

Chapters 2 and 3 are organized by clusters of functionally-related FE technologies for 

vehicles and trailers (e.g., tire systems, ITS, light-weighting materials, and aerodynamic systems) 

and alternative fuels, which are described and their respective associated potential safety issues 

are discussed. Chapter 2 summarizes the findings from a comprehensive review of available 

technical and trade literature and Internet sources regarding the benefits, potential safety hazards, 

and the applicable safety regulations and standards for deployed FE technologies and alternative 

fuels. Chapter 2 safety-relevant fuel-specific findings include:

• Both CNG- and LNG-powered vehicles present potential hazards, and call for wellknown engineering and process controls to assure safe operability and 

crashworthiness. However, based on the reported incident rates of NGVs and the 

experiences of adopting fleets, it appears that NGVs can be operated at least as safely 

as diesel MD/HDVs. 

• There are no safety contraindications to the large scale fleet adoption of CNG or LNG 

fueled heavy duty trucks and buses, and there is ample experience with the safe 

operation of large public transit fleets. Voluntary industry standards and best 

practices suffice for safety assurance, though improved training of CMV operators 

and maintenance staff in natural gas safety of equipment and operating procedures is 

needed.

• Observing CNG and LNG fuel system and maintenance facility standards, coupled 

with sound design, manufacture, and inspection of natural gas storage tanks will 

further reduce the potential for leaks, tank ruptures, fires, and explosions.

• Biodiesel blends used as drop-in fuels have presented some operational safety

concerns dependent on blending fraction, such as material compatibility, bio-fouling 

sludge accumulation, or cold-weather gelling. However, best practices for biodiesel 
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storage, and improved gaskets and seals that are biodiesel resistant, combined with 

regular maintenance and leak inspection schedules for the fuel lines and components 

enable the safe use of biodiesel in newer MD/HDVs

• Propane (LPG, or autogas) presents well-known hazards including ignition (due to 

leaks or crash) that are preventable by using Overfill Prevention Devices (OPDs), 

which supplement the automatic stop-fill system on the fueling station side, and 

pressure release devices (PRDs). Established best practices and safety codes (e.g., 

NFPA) have proven that propane fueled MD/HDVs can be as operationally safe as 

the conventionally-fueled counterparts. 

• As the market penetration of hybrid and electric drivetrain accelerates, and as the 

capacity and reliability of lithium ion batteries used in Rechargeable Energy Storage 

Systems (RESS) improve, associated potential safety hazards (e.g., electrocution from

stranded energy, thermal runaway leading to battery fire) have become well 

understood, preventable, and manageable. Existing and emerging industry technical 

and safety voluntary standards, applicable NHTSA regulations and guidance, and the 

growing experience with the operation of hybrid and electric MD/HDVs will enable 

the safe operation and large-scale adoption of safer and more efficient power-train 

electrification technologies. 

The safety findings from literature review pertaining to the specific FE technologies 

implemented to date in the MD/HDV fleet include:

• Telematics—integrating on-board sensors, video, and audio alerts for MD/HDV 

drivers—offer potential improvements in both driver safety performance and fuel 

efficiency. Both camera and non-camera based telematics setups are currently

integrated with available crash avoidance systems (such as ESC, RSC, LDWS, etc.) 

and appear to be well accepted by MD/HDV fleet drivers. 

• Both experience abroad and the cited US studies of trucks equipped with active speed 

limiters indicated a safety benefit, as measured by up to 50 percent reduced crash 

rates, in addition to fuel savings and other benefits, with good CMV driver 

acceptance. Any negative aspects were small and avoidable if all the speed limitation 

devices were set to the same speed, so there would be less need for overtaking at 

highway speeds.

• No literature reports of adverse safety impacts were found regarding implementation 

of on-board idle-reduction technologies in MD/HDVs (such as automatic start-stop, 

direct-fired heaters, and APUs).
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• There was no clear consensus from the literature regarding the relative crash rates and 

highway safety impacts of LCVs, due to lack of sufficient data and controls and 

inconsistent study methodologies. Recent safety evaluations of LCVs and ongoing 

MAP-21 mandated studies will clarify and quantify this issue.

• Tire technologies for FE (including ATIS, TPMS, LRR and single-wide tires) 

literature raised potential safety concerns regarding lower stability or loss of control, 

e.g., when tire pressure is uneven or a single wide tire blows out on the highway. 

However, systems such as automated tire monitoring systems and stability enhancing 

electronic systems (ABS, ESC, RSC) may compensate and mitigate any adverse 

safety impacts. 

• Aerodynamic technologies that offer significant fuel savings have raised potential 

concerns about vehicle damage or injury in case of detached fairings or skirts, 

although there were no documented incidents of this type in the literature. 

• Some light weighting materials may pose some fire safety and crashworthiness 

hazards, depending on their performance in structural or other vehicle subsystem 

applications (chassis, power-train, and crash box or safety cage). Some composites 

(fiberglass, plastics, CFRC, foams) may become brittle on impact or due to 

weathering from UV exposure or extreme cold. Industry has developed advanced, 

high performance lightweight material options tailored to their automotive 

applications, e.g., thermoplastics resistant to UV and weathering. No examples of 

such lightweight material failures on MD/HDVs were identified in the literature. 

Chapter 3 provides complementary inputs on the potential safety issues associated with 

FE technologies and alternative fuels obtained from Subject Matter Experts (SMEs). The broad 

cross-section of SMEs consulted had experience with the operation of “green” truck and bus 

fleets, were Federal program managers, or were industry developers of FE systems for 

MD/HDVs. Safety concerns raised by the SMEs can be prevented or mitigated by complying 

with applicable regulations and safety standards and best practices, and are being addressed by 

evolving technologies, such as electronic collision prevention devices. Although SMEs raised 

some safety concerns, their experience indicates that system- or fuel-specific hazards can be 

prevented or mitigated by observing applicable industry standards, and by training managers, 

operators and maintenance staff in safety best practices. Specific safety concerns raised by 

SMEs based on their experience included:

• Alternative fuels did not raise major safety concerns, but generally required better 

education and training of staff and operators. There was a concern expressed 

regarding high pressure (4000 psi) CNG cylinders that could potentially explode in a 

crash scenario or if otherwise ruptured. However, aging CNG fuel tank safety can be 

assured by enforcing regulations such as FMVSS No. 304, and by periodic inspection 
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and end-of-life disposal and replacement. A propane truck fleet manager stated that 

the fuel was as safe as or safer than gasoline, and reported no safety issues with the 

company’s propane, nor with hybrid gasoline-electric trucks. OEMs of drivetrain 

hybridization and electrification systems, including advanced Lithium Ion batteries 

for RESS, indicated that they undergo multiple safety tests and are designed with failsafes for various misuse and abuse scenarios. Integration of hybrid components 

downstream by bodybuilders in retrofits, as opposed to new vehicles, was deemed a 

potential safety risk. Another potential safety concern raised was the uncertain 

battery lifetime due to variability of climate, duty-cycles, and aging. Without stateof-charge indicators, this could conceivably leave vehicles underpowered or stranded 

if the battery degrades and is not serviced or replaced in a timely manner. 

• ITS and telematics raised no safety concerns; on the contrary, fleet managers stated 

that “efficient drivers are safer drivers.” Monitoring and recording of driver behavior, 

combined with coaching, appeared to reduce distracted and aggressive driving and 

provided significant FE and safety benefits. 

• A wide-base single tire safety concern was the decrease in tire redundancy in case of 

a tire blowout at highway speeds. For LRRs, a concern was that they could 

negatively affect truck stopping distance and stability control.

• A speed-limiter safety concern was related to scenarios when such trucks pass other 

vehicles on the highway instead of staying in the right-hand lane behind other 

vehicles. By combining speed limiters with driver training programs, overall truck 

safety could actually improve, as shown by international practice. 

• Aerodynamic systems’ safety performance to date was satisfactory, with no instances 

of on-road detaching. However, covering underside or other components with 

aerodynamic fairings can make them harder to inspect, such as worn lugs, CNG relief 

valve shrouds, wheel covers, and certain fairings. Drivers and inspectors need to be 

able to see through wheel covers and to be able to access lug nuts through them. 

These covers must also be durable to withstand frequent road abuse. 

• For lightweighting materials, the safety concern raised was lower crashworthiness 

(debonding or brittle fracture on impact) and the potential for decreased survivability

in vehicle fires depending on the specific material choice and its application. 

The key finding from the literature review and SME interviews is that there appear to be 

no major safety hazards preventing the adoption of FE technologies, or the increased use of 

alternative fuels and vehicle electrification. In view of the scarcity of hard data currently 

available on actual highway crashes that can be directly or causally attributed to adoption of FE 
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technologies and/or alternative fuels by MD/HDVs, and the limited experience with commercial 

truck and transit bus fleets operations equipped with these technologies, it was not possible to 

perform a quantitative, probabilistic risk assessment, or even a semi-quantitative preliminary

hazard analysis (PHA).

Chapter 4 employs a deterministic scenario-based hazard analysis of potential crash or 

other safety concerns identified from the literature review or raised by subject matter experts 

(SMEs) interviewed (e.g., interfaces with charging or refueling infrastructure). For each specific 

hazard scenario discussed, the recommended prevention or mitigation options, including 

compliance with applicable NHTSA or FMCSA regulations, and voluntary industry standards 

and best practices are identified, along with FE technology or fuel-specific operator training.

SMEs safety concerns identified in Sec 3.3 were complemented with actual incidents, and 

developed into the hazard scenarios analyzed in Chapter 4.

The scenario-based deterministic hazard analysis reflected not only the literature findings 

and SMEs’ safety concerns, but also real truck or bus mishaps that have occurred in the past.

Key hazard analysis scenarios included: CNG-fueled truck and bus vehicle fires or explosions 

due to tank rupture, when pressurized fuel tanks were degraded due to aging or when PRDs 

failed; LNG truck crashes leading to fires, or LNG refueling-related mishaps; the flammability or 

brittle fracture issues related to lightweighting materials in crashes; reduced safety performance 

for either LRR or wide-base tires; highway pile-ups when LCVs attempt to pass at highway

speeds; aerodynamic components detaching while the vehicle traveled on a busy highway or 

urban roadway; and fires resulting in overheated lithium ion batteries in electric or hybrid buses. 

These hypothetical worst case scenarios appear to be preventable or able to be mitigated by 

observing safety regulations and voluntary standards, or with engineering and operational best 

practices. 

Chapter 5 reviews and discusses the existing federal and state regulatory framework for 

safely operating MD/HDVs equipped with FE technologies or powered by alternative fuels. The 

review identifies potential regulatory barriers to their large-scale deployment in the national fleet 

that could delay achievement of desired fuel consumption and environmental benefits, while 

ensuring equal or better safety performance.

Chapter 6 summarizes the major findings and recommendations of this preliminary safety 

analysis of fuel efficiency technologies and alternative fuels adopted by MD/HDVs. The 

scenario-based hazard analysis, based on the literature review and experts’ inputs, indicates that 

MD/HDVs equipped with advanced FE technologies and/or using alternative fuels have 

manageable potentially adverse safety impacts. The findings suggest that the potential safety 

hazards identified during operation, maintenance, and crash scenarios can be prevented or 

mitigated by complying with safety regulations and voluntary standards and industry best 

practices. The study also did not identify any major regulatory barriers to rapid adoption of FE 

technologies and alternative fuels by the MD/HDV fleet. 
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9.5 Oak Ridge National Laboratory (ORNL) Research on Low Rolling 

Resistance Truck Tires

DOT’s Federal Motor Carrier Safety Administration and NHTSA sponsored a test 

program conducted by Oak Ridge National Laboratory to explore the effects of tire rolling 

resistance levels on Class 8 tractor-trailer stopping distance performance over a range of loading 

and surface conditions.DThe objective was to determine whether there is a relationship between 

tire rolling resistance and stopping distance for vehicles of this type. The overall results of this 

research suggest that tire rolling resistance is not a reliable indicator of Class 8 tractor-trailer 

stopping distance. The correlation coefficients (R2 values) for linear regressions of wet and dry

stopping distance versus overall vehicle rolling resistance values did not meet the minimum 

threshold for statistical significance for any of the test conditions. Correlation between CRR and 

stopping distance was found to be negligible for the dry tests for both loading conditions. While 

correlation was higher for the wet testing (showing a slight trend in which lower CRRs 

correspond to longer stopping distances), it still did not meet the minimum threshold for 

statistical significance. In terms of compliance with Federal safety standards, it was found that 

the stopping distance performance of the vehicle with the four tire sets studied in this research 

(with estimated tractor CRRs which varied by 33 percent), were well under the FMVSS No. 121 

stopping distance requirements. 

9.6 Additional Safety Considerations

The agencies’ considered the Organic Rankine Cycle waste heat recovery (WHR) as a 

fuel saving technology in the rulemaking timeframe. The basic approach of these systems is to 

use engine waste heat from multiple sources to evaporate a working fluid through a heat 

exchanger, which is then passed through a turbine or equivalent expander to create mechanical or 

electrical power. The working fluid is then condensed as it passes through a heat exchanger and 

returns to back to the fluid tank, and pulled back to the flow circuit through a pump to continue 

the cycle. Despite the promising performance of pre-prototype WHR systems, manufacturers 

have not yet arrived at a consensus on which working fluid(s) to be used in WHR systems to 

balance concerns regarding performance, global warming potential (GWP), and safety. Current 

working fluids have a high GWP (conventional refrigerant), are expensive (low GWP 

refrigerant), are hazardous (ammonia, etc.), are flammable (ethanol/methanol), or can freeze 

(water). One of the challenges is determining how to seal the working fluid properly under the 

vacuum condition with high temperature to avoid safety issues for flammable/hazardous working 

fluids. Because of these challenges, choosing a working fluid will be an important factor for 

system safety, efficiency, and overall production viability. The agencies believe manufacturers 

will require additional time and development effort to assure that a working fluid that is both 

appropriate, given the noted challenges, and has a low GWP for use in waste heat recovery

systems. Based on this and other factors, the analysis for the Preferred Alternative assumes that 

WHR would not achieve a significant market penetration for diesel tractor engines (i.e., greater 

 

D Lascurain, M.B. (2015, June). “Effects of tire rolling resistance levels on Class 8 tractor trailer stopping distance 

performance.” Washington, DC: National Highway Traffic Safety Administration.
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than 5 percent) until 2027, which would provide time for these considerations to be addressed. 

The agencies assume no use of this technology in the HD pickups and vans and vocational 

vehicle segments. 

9.7 The Agencies’ Assessment of Potential Safety Impacts

NHTSA and EPA considered the potential safety impact of technologies that improve HD 

vehicle fuel efficiency and GHG emissions as part of the assessment of regulatory alternatives. 

The safety assessment of the technologies in this proposal was informed by two NAS reports, an 

analysis of safety effects of HD pickups and vans using estimates from the DOT report on the 

effect of mass reduction and vehicle size on safety, and agency-sponsored safety testing and 

research. The agencies considered safety from the perspective of both direct effects and indirect 

effects.

In terms of direct effects on vehicle safety, research from NAS and Volpe, and direct 

testing of technologies like the ORNL tire work, indicate that there are no major safety hazards 

associated with the adoption of technologies that improve HD vehicle fuel efficiency and GHG 

emissions or the increased use of alternative fuels and vehicle electrification. The findings 

suggest that the potential safety hazards identified during operation, maintenance, and crash 

scenarios can be prevented or mitigated by complying with safety regulations, voluntary

standards and industry best practices. Tire testing showed tire rolling resistance did not impact 

of Class 8 tractor-trailer stopping distance for the tires tested. Also, because the majority of HD 

pickup and van fleet are above 4,594 pounds, the vehicle mass reduction in HD pickup and vans 

is estimated to reduce the net incidence of highway fatalities. Taken together, these studies 

suggest that the fuel efficiency improving technologies assessed in the studies can be 

implemented with no degradation in overall safety.

However, analysis anticipates that the indirect effect of the proposed standards, by

reducing the operating costs, would lead to increased travel by tractor-trailers and HD pickups 

and vans and, therefore, more crashes involving these vehicles.