[Congressional Record (Bound Edition), Volume 154 (2008), Part 18]
[Senate]
[Pages 24766-24767]
[From the U.S. Government Publishing Office, www.gpo.gov]




               GOVERNMENT ACCOUNTABILITY OFFICE ANALYSIS

  Mr. WARNER. Madam President, earlier this summer, when gasoline 
prices were topping $4 a gallon, I asked the GAO to analyze potential 
savings from the establishment of a national speed limit. I did not 
prescribe what that speed limit should be, merely asked the GAO to 
conduct an analysis at which speeds vehicles were most fuel efficient 
and make a determination as to whether a national speed limit would 
have positive impacts on the conservation of gasoline.
  My interest in this approach to gas conservation was spurred by a 
desire for a measure that would provide immediate relief to the 
overstretched budgets of households across America. I was also dusting 
off a solution used in the past, specifically, the number of barrels of 
oil saved when a national

[[Page 24767]]

speed limit was imposed in 1974 in response to the Arab oil embargo.
  Last week, I was pleased to meet with the GAO and hear their findings 
on the relationship between vehicular speed and fuel economy as well as 
how reducing the speed limit might affect fuel use and perhaps cost.
  While the days of my service in the U.S. Senate are numbered, it is 
my hope that these findings by the GAO can serve as a useful tool to my 
colleagues who will return in the next Congress, as I know the 
interlinked issues of energy, transportation, and climate change are 
going to remain the focus of much debate and policy making in the 
coming years.
  Mr. President, I thank the GAO for its work, and I ask unanimous 
consent that GAO analysis be printed in the Record.
  There being no objection, the material was ordered to be printed in 
the Record, as follows:

     Energy Efficiency: Potential Fuel Savings Generated by a 
         National Speed Limit Would Be Influenced by Many Other 
         Factors
       In response to Senator Warner's interest in obtaining 
     information on the possibility of using a national speed 
     limit to reduce fuel consumption, the Government 
     Accountability Office reviewed existing literature and 
     consulted knowledgeable stakeholders on the following:
       What is the relationship between speed and the fuel economy 
     of vehicles?
       How might reducing the speed limit affect fuel use?
       Due to a limited time frame of two months to complete the 
     work, to address these objectives, we limited our analyses to 
     light-duty vehicles, such as cars, sport utility vehicles, 
     and pickup trucks and relied on the expertise of GAO and 
     knowledgeable stakeholders to identify the most relevant 
     economic and transportation literature. We provided a draft 
     to the three agencies whose officials we consulted for our 
     analyses--the Environmental Protection Agency (EPA), the 
     Department of Energy (DOE), and the Department of 
     Transportation (DOT)--and incorporated relevant technical 
     comments. We did not examine other aspects of implementing a 
     national speed limit, such as potential safety impacts. In 
     summary, we found the following.
     According to Literature and Stakeholders, Reducing a 
         Vehicle's Speed Can Potentially Increase Its Fuel 
         Economy, Depending on the Vehicle's Characteristics
       For a vehicle traveling at high speed, reducing its speed 
     increases fuel economy. In general, at speeds over 
     approximately 35 to 45 mph, if a vehicle reduces its speed by 
     5 mph, its fuel economy can increase by about 5 to 10 
     percent, because air resistance, or drag, increases 
     exponentially as a vehicle goes faster. Conversely, air 
     resistance diminishes more rapidly as a vehicle slows down, 
     thus increasing its fuel economy.
       According to existing literature and knowledgeable 
     stakeholders, there is no single speed that optimizes fuel 
     economy for all vehicles. Optimal speed for fuel economy for 
     individual vehicles ranges widely, but is generally between 
     30 and 60 mph, depending on a vehicle's characteristics. For 
     example, according to the most recent published data--a 1997 
     study by Oak Ridge National Laboratory, commissioned by the 
     Federal Highway Administration (FHWA), that examined fuel 
     economy at different speeds for nine automobiles and light 
     trucks from model years 1988 through 1997--the optimal fuel 
     economy for a 1994 Jeep Grand Cherokee, a sport-utility 
     vehicle, would be about 26 miles per gallon at a steady 40 
     mph. In contrast, in a 2008 internal study by the Argonne 
     National Laboratory for the Department of Energy (DOE), 
     examining four vehicles, the optimal fuel economy for a 2005 
     Toyota Echo, a subcompact car, is about 69 miles per gallon, 
     achieved when traveling at a steady 30 mph.
       However, a vehicle's fuel economy also depends on other 
     factors besides air resistance. Factors that enhance fuel 
     economy include engine efficiency enhancements (e.g., fuel 
     injection), electronic and computer controls, more efficient 
     transmissions, and hybrid technology. However, other factors, 
     such as increased vehicle weight, decrease fuel economy.
       In general, over the last 2 decades, fuel economy gains 
     resulting from advances in automotive technologies have 
     largely been offset by increases in vehicle weight, 
     performance, and accessory loads. Specifically, vehicles are 
     heavier than in the past, because they are larger and include 
     more technologies. For example, average vehicle weight has 
     increased from 3,220 pounds in 1987 to 4,117 in 2008, 
     according to the Environmental Protection Agency (EPA). In 
     addition, trends show that recent vehicles, on average, have 
     bigger, more powerful engines that yield better performance--
     i.e., acceleration and greater speed--at the expense of fuel 
     economy. For example, according to the same EPA report, 
     average horsepower has increased from 118 to 222 over the 
     same period. Further, increased accessory loads, such as air 
     conditioning and electronics, have also reduced fuel economy. 
     According to EPA, from 1987 through 2004, on a fleetwide 
     basis, technology innovation was utilized exclusively to 
     support market-driven attributes other than fuel economy, 
     such as performance. Beginning in 2005, however, according to 
     EPA's analysis of fuel economy trends, technology has been 
     used to increase both performance and fuel economy, while 
     keeping vehicle weight relatively constant.
     According to Literature and Stakeholders, a Reduced Speed 
         Limit Is Only One of Many Factors That Could Affect Total 
         Fuel Use
       Lowering speed limits can potentially reduce total fuel 
     consumption. According to literature we reviewed examining 
     the impact of the national speed limit enacted in 1974, the 
     estimated fuel savings resulting from the 55 mph national 
     speed limit ranged from 0.2 to 3 percent of annual gasoline 
     consumption. According to DOE's 2008 estimate, a national 
     speed limit of 55 mph could yield possible savings of 175,000 
     to 275,000 barrels of oil per day. This range is consistent 
     with estimates of the impact of the past national speed 
     limit. According to the Energy Information Administration, 
     total U.S. consumption of petroleum for 2007 was about 21 
     million barrels of oil per day.
       However, other factors, including drivers' compliance with 
     a reduced speed limit, would affect the actual impact of a 
     lower speed limit on the amount of fuel savings. Reducing the 
     speed limit does not necessarily mean that drivers will 
     comply. In fact, in 1975, under the previous national speed 
     limit, about half of the states reported more drivers 
     exceeding the national speed limit of 55 mph than complying 
     with it. States may vary in their ability to enforce the 
     reduced speed limit, in part due to cost and limited 
     resources, affecting driver compliance. Moreover, a national 
     speed limit would not affect many of the miles driven in the 
     United States, such as those in urban areas, where most 
     vehicles are already traveling at lower speeds due to lower 
     speed limits or congestion. According to FHWA, fewer than one 
     quarter of the vehicle miles traveled (VMT) in the United 
     States would likely be directly affected by a changed speed 
     limit. In addition, congestion forces some vehicles to travel 
     slowly, no matter what the speed limit, meaning a reduction 
     would have little or no impact on fuel consumed on congested 
     roads.
       Other external conditions also affect fuel economy, such as 
     road conditions, including whether a road is steep or flat, 
     and weather conditions, including wind speed and direction. 
     Finally, other aspects of driver behavior may also affect 
     fuel consumption. For example, driver behavior may be 
     affected by fuel prices. Higher prices may cause people to 
     drive less or purchase more fuel-efficient vehicles. 
     Similarly, driving at a consistent speed can reduce fuel 
     consumption. In contrast, aggressive driving such as 
     accelerating or stopping quickly can increase fuel 
     consumption. In addition, proper vehicle maintenance--
     including regularly changing automobile fluids and filters 
     and properly inflating tires--improves fuel economy.
       The speed limit is only one tool among many for potentially 
     conserving fuel. Certain realities such as congestion on our 
     nation's roads, how people drive and maintain their vehicles, 
     and emerging technologies are other potential considerations 
     as the nation looks for options to conserve fuel.

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