The largest source of U.S. carbon emissions comes from the Transportation Sector’s petroleum consumption.  The Federal Government has attempted to reduce Transportation petroleum consumption by requiring increased Corporate Average Fuel Efficiency (CAFE) standards for new ‘light duty vehicles’ (LDV) since 1978.  While the new CAFE standards succeeded in reducing Transportation Sector petroleum consumption 1978-1995, the continued growth in the number of LDV’s and annual ‘vehicle miles traveled’ (VMT) has led to almost a continuous increase in petroleum consumption until 2007.  

Recent analysis of the factors that have contributed most towards reduced U.S. carbon emissions since 2007 indicates that CAFE standards are the second largest contributing factor.  To build on this recent success and further reduce future U.S. carbon emissions from LDV’s what innovative technologies will be needed to make substantially greater progress?

Recent CAFE History and Performance

The Obama Administration recently increased the Federal CAFE standards.  While these latest LDV fuel efficiency standards are a good build on the previous Administration’s CAFE improvements, the DOE/EIA still projects that the U.S. Transportation Sector’s total petroleum consumption will remain essentially constant through 2023.  Re: AEO 2013 Table 11: by Sector Transportation.    Past CAFE standards performance unfortunately stagnated through the 1990’s and most the 2000’s.  This was not only due to increased number of LDV’s and AMT, but also relative small improvement in CAFE standards during most the period and numerous ‘loopholes’ that compromised the performance of past standards.  Past loopholes included classifying SUV’s as trucks with less efficient CAFE standards, giving auto manufacturers credits for producing ‘flex-fuel vehicles’ that rarely operate on E-85, allowing significant non-compliance luxury-high performance vehicle sales with nominal penalties, and, very significant LDV performance differences between actual on-road fuel efficiencies and the CAFE standards. 

One of the largest differences between actual LDV on-road fuel efficiency or ‘miles per gallon’ (mpg) and CAFE standards (excluding all regulatory loopholes) has to do with how the CAFE tests are carried out.  The CAFE tests are normally carried out in a laboratory on a dynamometer test stand based on a city/highway standard speeds of 55/45 ‘miles per hour’ (mph).  No accessories such as ‘air conditions’ (AC) are used during testing.  While the CAFE standard test does meet the need for accuracy and data consistency between different vehicles-years, consumers early on recognized that actual on-road driving mpg rarely duplicated the CAFE window sticker.  This has to do with the fact that LDV mpg performance is a function of how and where the vehicle is actually driven. 

To correct for the differences between ‘unadjusted’ laboratory CAFE performance data and actual LDV operations the EPA has developed an ‘adjusted’ mileage efficiency to better inform consumers of expected on-road actual mpg.  The adjusted new LDV mpg data are based on driving conditions closer to what most vehicle owners should expect including more realistic highway/city mph speeds and use of vehicle accessories such as AC.  Refer to the following graph.

U.S. CAFE and EPA Adjusted Vehicle Fuel Mileage – 1975-2009



Data source: EPA ’Light Duty Automotive Technology and Fuel Economy Trends’.  Note: LAB – unadjusted CAFE laboratory data and EPA Adj. – adjusted CAFE standard to more reasonably duplicate actual on-road LDV fuel efficiencies.

These adjusted mpg fuel efficiency data indicate that on average consumers should expect to get only about 80% of posted CAFE standard gasoline mpg determined in the laboratory.  

Vehicle Fuel Efficiency is a Function of Technology and Driver Behavior

Most drivers recognize that in-town stop-and-go driving LDV mpg performance is much poorer than constant speed highway driving (within speed limits).  This has to do with the normal engine performance efficiencies, which are lower in acceleration-speedup modes than at constant speeds.  Also if the driver is more aggressive like a teenager racing from stoplight-to-stoplight, the vehicle mpg will be much lower than less aggressive drivers.  Professional Racecar drivers primarily operate in only two modes: on the accelerator or on the brakes.  This aggressive driving mode leads to maximum average vehicle speeds and minimum lap-times, but also substantially reduces fuel efficiency.

Over the years Automotive Manufacturers have made numerous improvements and innovations in order to meet CAFE standards.  Besides making many LDV’s smaller and lighter, a broad number of improvements have been developed to substantially increase ‘internal combustion engine’ (ICE) motor efficiency and performance (horsepower (hp), torque and acceleration).  Engine efficiency innovations have included a broad number of ICE upgrades including direct fuel injection, computer controlled fuel:air ratios, new turbochargers and transmissions, and other efficiency upgrades.  The development of new ‘hybrid electric vehicle’ (HEV) technologies has also made significant contributions towards increased overall LDV fleet efficiency.  One of the most innovative technologies is the HEV drive-train with ‘regenerative braking’.  Rather than wasting the energy from slowing-stopping the vehicle (brake pad wear-heat loss), the regenerative braking system stores some of the energy by charging a battery, which later powers the vehicle (EV mode) and displaces some ICE fuel consumption.  Another innovative technology is an engine-integrated starter-generator system (ISG) that automatically stops-starts the ICE and saves fuel from wasteful idling.    

All of the above referenced technology innovations and use of smaller, lighter vehicles has allowed LDV Manufacturers to meet their CAFE standard requirements and general consumer market demands.  The problem statement continues to be how to best further increase actual average LDV fuel efficiency, and the opportunity is how to possibly narrow the difference between actual on-road mpg performance and the unadjusted CAFE standards.   If the actual on-road or EPA adjusted LDV mpg could be increased more towards the unadjusted CAFE standards it should be possible to further and very significantly reduce U.S. petroleum consumption and associated carbon emissions.

One of the highest mileage HEV’s available today is the Toyota Prius with combined highway/city average of 50 mpg.  But, even the Prius will fail to get its advertised fuel mileage if driven very aggressively; maximum acceleration between stops and hard on the brakes at each stop.  How can the Federal Government and Automotive Manufacturers develop a new ‘Smart Driver’ technology needed to ensure drivers do not waste petroleum motor fuels and increase their LDV carbon emissions?

Innovative ‘Smart Driver’ Technology Development

Maximizing ICE LDV fuel efficiency began over 40 years ago.  One of the first technology innovations involved monitoring the intake manifold vacuum (via a mechanical vacuum gauge).  Maximizing fuel efficiency required maximizing manifold measured vacuum and minimizing vacuum loss during acceleration (for carburetor fuel systems).  The decision to minimize loss of vacuum and fuel consumption was totally at the driver’s discretion.  The next historic development to help maximize ICE LDV fuel efficiency was ‘cruise control’.  Operating on cruise control to maintain constant speeds helps maximize LDV fuel efficiency under most conditions.

Over the years the technologies of ICE’s and advanced efficiency controls evolved.  Earlier ICE electronic controls were focused primarily on tailpipe emissions.  Fortunately, significant synergies exist between minimum tailpipe emissions and maximum fuel efficiencies.  Advanced emission controls helped limit the amount of fuel consumption (and unfortunately earlier LDV ICE performances) in order to minimize tailpipe emissions.  Use of emission control systems was not discretionary and required by law. 

In recent years a broad range of ICE technology innovations (as previously discussed) have not only increased fuel efficiency, restored past lost ICE performance, and have done so while meeting all EPA tailpipe emission requirements.  While compact LDV’s such as the current (HEV) Prius almost meet the latest new 54.5 mpg CAFE standard required in 2025, other larger LDV’s such as full size automobiles, SUV’s and trucks will face a potentially enormous technology challenge in order to comply with future CAFE standards (and do so without taking advantage of loopholes that can result in much less than 54.5 mpg CAFE performance).  One of the very important factors to meeting future CAFE standards will be ‘engine-advanced efficiency controls’ (EAEC) technology development.  In addition to further ICE mechanical upgrades and developments, advanced EAEC programming would monitor engine-vehicle performance and driving conditions and adjust fuel:air ratios, ignition timing, transmission shifting, etc. to minimize tailpipe emissions and maximize overall vehicle fuel efficiency and driving performance.

All vehicles built today have engine computer systems to control tailpipe emissions and help minimize fuel consumption.  Tailpipe emissions are usually programmed as the first priority function over engine performance and fuel efficiency.  To maximize the fuel efficiency of future state-of-art LDV’s generally involves optimizing engine performance under conditions of acceleration, constant speed and slowing/stopping.  Many vehicles have computers that monitor and continuously display actual LDV mpg performance, to help drivers possibly adjust their driving habits to reduce fuel consumption.  Increasing fuel efficiency by reducing the rate of acceleration, maintaining constant speed where possible and minimize braking is still left up to the discretion of individual drivers. 

To reduce the average ‘unadjusted-adjusted’ CAFE mpg differences in the future will very likely mean slowing down somewhat for most any type or advancement in ICE, HEV and possibly PHEV or EV technologies (yes, maximum acceleration and variable speeds can waste electric power capacity in PHEV/EV’s also).  This means reduced acceleration, maximizing constant speed-cruise control and reduced braking needed to safely navigate city roadways and inter-city highways.  The solution to increasing any vehicle’s fuel efficiency is to develop more advanced energy efficiency computer control systems or what could be called ‘Smart Driver’ computer control technology.  Effective Smart Driver ICE LDV computer control systems would possibly take the some of the current vehicle operating discretion away from the driver and make maximizing fuel consumption of equal importance to controlling tailpipe emissions.

Innovative ‘Smart Driver’ Technology Could Build on Developing ‘Driverless Car’ Technology

A high priority is being placed on developing the technologies required to increase LDV fuel efficiency.  The DOE sponsored Oak Ridge National Laboratory research project is an excellent example.  In addition to ICE technology innovations, a new evolving technology, Goggle’s ‘Driverless Car’, is receiving a lot of interest and support.

The Driverless Car technology includes very detailed programming of existing roads mapping with speed limits data and a sophisticated GPS.  In addition, the installation of various motion & light sensors, combined with complex programming needed to address all driving variables, including stop lights and the variables that can’t be pre-programmed such as other moving or stopped vehicles, and other changing-mobile road obstacles or potential hazards.  The combination of these technologies allows Driverless Cars to safely navigate through traffic from most any starting point to a programmed final destination automatically (driverless).

Developing a new Smart Driver technology to maximize LDV fuel efficiency could be based largely on both existing EAEC and Driverless Car technologies.  New Smart Driver controlled and higher fuel efficiency LDV’s could be programmed to optimize vehicle overall performance needed to travel from any starting point to final destination.  The level of needed acceleration and reduced speed/stopping could be optimized around established roads/highways, speed limits, and stop signs/lights.  While the driver would still operate the vehicle’s steering manually, have the option of changing routes, and some flexibility over the accelerator/brakes, the feasible new Smart Driver computer control technology would help maintain optimal acceleration, constant speeds (within established speed limits) and anticipate slowing/stopping as needed to optimize and maximize overall LDV fuel efficiency (and minimize carbon emissions).

Potential Benefits of Innovative ‘Smart Driver’ Technology

The U.S. Transportation Sector LDV’s currently (2012) consume 8.4 million barrels per day (MBD) of petroleum motor fuels.  Consumption of these petroleum motor fuels contributes about 1,050 million metric tons (MMT) per year of total U.S. carbon dioxide (CO2) emissions; of the total U.S. 5,290 MMT CO2 per year in 2012.  Installing new Smart Driver technology in all ICE LDV’s has the potential of making the difference between actual on-road fuel efficiency and unadjusted (lab.) CAFE standards essentially zero.  This would reduce LDV fuel consumption by up to 20% and reduce current carbon emissions by up to (1050 x 0.2 =) 210 MMT CO2 per year.  This CO2 reduction is equivalent to shutting down up to almost 14% of all existing Power Sector coal generation capacity.  In addition, total petroleum oil imports could be reduced by up to (8.4 x 0.2 =) 1.7 MBD, which represents almost 80% of all current highest risk OPEC Persian Gulf imports.  This would substantially improve current U.S. Energy Security.   

One additional and very significant potential benefit of Smart Driver computer control technology upgrades could be increased vehicle operating safety.  By better controlling vehicle acceleration, maximum speeds, and the addition of anti-collision technologies, a new Smart Driver technology could also substantially reduce vehicle collisions, injuries and fatalities.  Vehicle fatalities currently average 30,000-35,000 per year in the U.S.  A new Smart Driver technology could reduce a very large percentage of these fatalities in future years.

The development and installation of Smart Driver (or equivalent) technology can make future LDV’s much more efficient, less polluting and safer to operate.  The next challenge will be to get Consumers to accept the fact that the operation of their LDV’s must slow down a bit and not allow exceeding speed limits.  Yes, driving future Smart Driver controlled LDV’s may be a little boring to those who prefer to drive more aggressively, but what’s more important in the future?  Reduced carbon emissions, increased energy security and saving thousands of people’s lives, or allowing and tolerating more aggressive, riskier driving habits.