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Environmental Impacts of Removing National Speed Limit Requirements |
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Date: November 30, 1995
MEMORANDUM
Subject: Environmental Impacts of Removing National Speed Limit
Requirements
To: Regional Air Directors
Regional Air Branch Chiefs
Regional Air Section Chiefs
Regional Transportation Staff
From: Bob Noland, OPPE, 202-260-2418
Laura Gottsman, OPPE, 202-260-9247
Will Schroeer, OPPE, 202-260-1126
cc: Robin Miles-McLean
Maryann Froehlich
Steve Lipman
Steve Cochran
Lucy Audette
Several people have been asked how the elimination of the federal speed limit, recently signed into law as part of the National Highway System Bill, will affect air quality. We have done an analysis of the effect on auto emissions, and hope that it is useful to you. You may want to share this information with the state air quality agencies with whom you work. The MOBILE5a runs on which the analysis is based are available upon request.
Background
The 55 mph national speed limit was originally introduced on Jan. 1, 1974, in response to the Arab oil embargo and subsequent energy crisis. While this restriction was not mandated by the Federal government, highway funding was linked to the adoption of the speed limit (and its enforcement) by the states. In 1987, this was modified to allow maximum speed limits on rural interstate freeways to increase to 65 mph. Prior to the adoption of these limits, most states had speed limits of 70 mph (with some having limits as high as 75 mph and Montana and Wyoming having no maximum limits). only one state, New York, had a 55 mph speed limit prior to 1974. Speed limit increases will raise NOx emissions by at least 5%
The National Highway System Bill just signed by the President eliminates the federal national speed limit requirements for non-commercial vehicles. Since emissions of the ozone pre-cursor NOx increase as vehicle speeds increase above about 48 mph, speed limit changes may have important consequences for ozone nonattainment areas. Raising speed limits will affect the ability of some areas to reach attainment status, and of other areas to stay in compliance.
EPAs MOBILE5a emissions model shows that national NOx emissions would increase at least 5 percent in the following scenario: urban speed limits remain unchanged and rural speed limits increase to 65 mph except that those states with limits below 65 mph before 1974 would maintain those lower limits.
There are various reasons to believe this is a low estimate of the impact. New York state, for example, recently increased its rural speed limits to 65 mph, exceeding their pre-1974 maximum speed limit. Several states have already increased their speed limits to 70 and 75 mph. More states may follow suit; before 1974, most states had limits higher than 65 mph.
The 65 mph limit was modeled primarily because of the limitations of MOBILE5a, which is only capable of analyzing emissions at speeds up to 65 mph. In addition, actual average driving speeds may exceed 65 mph, as is discussed further below. State-by-state increases may be much higher. Under the above scenario, MOBILE5a shows NOx emissions may increase as much as 9 percent in portions of the I-95 corridor from Virginia to Maine.
* Increased NOx emissions may make it more difficult to meet attainment deadlines, and increase costs of compliance with NAAQS Even if NOx emissions were only to increase in rural areas, those emissions could hamper efforts of nonattainment areas to reach attainment because NOx emitted in an attainment region one day often migrates to a nonattainment region the next day.
If states decide that these increases in mobile NOx sources are acceptable, they may face other costs to reduce ozone formation and meet or maintain National Ambient Air Quality Standards (NAAQS). For example, they may have to increase controls on industrial sources of NOx, including utility and industrial boilers. These controls will be more costly than maintaining current speed limits. Employers may also have to consider more stringent Traffic Control Measures to increase vehicle occupancy levels for work trips.
* Speed limit increases will raise CO emissions
Increased motor-vehicle speeds are likely to also increase CO emissions (Pechan, 1992). These emissions also result from the combustion process and will increase at speeds above 48 mph. Based upon similar reasoning, one could also expect increases in particulate matter (PM).
* Speed limit increases will raise CO2 (greenhouse gas) emissions
Vehicle fuel economy decreases as vehicle speeds increase, and markedly so above speeds of about 50 mph. The removal of current speed limits would significantly increase fuel use for the same amount of national vehicle travel, making Greenhouse Gas reduction targets more difficult to meet. EPA analysis indicates that carbon emissions would increase by 6-15 million metric tons of carbon equivalent (mmtCe) per year, or about 6-15% of the amount needed to return U.S. emissions to 1990 levels in the year 2000.
* Driver response is uncertain, but may contribute to progressively higher travel speeds (and therefore emissions) over time
One unanswered question is how drivers will respond to higher speed limits. Currently, a majority of drivers exceed the posted speed limit (FHWA, 1994). Average travel speed on urban interstates is about 59 mph, while on rural interstates it is about 61 mph. Prior to the setting of national speed limits in 1974, the average on rural interstates was 65 mph (for uncongested travel).
Generally, drivers prefer to maintain speeds similar to others traveling near them. It can be anticipated that the removal of legal restrictions against higher speeds (i.e., removal of the cost of being cited for speeding) will result in an average increase in speeds.
Increases in average speeds has been a consistent trend over the last 20 years. This has been fueled partly by better and safer road designs and by the design of safer automobiles. It is far more likely that an automobile driver will survive an accident today than 20 years ago. Therefore, the risks associated with higher speeds are not as great as they once were, and hence, all else equal, we can expect average speeds to exceed levels that existed prior to 1974.
Faster automobile traffic will have other effects which are likely to magnify the direct increase in emissions. Travel times will be reduced due to higher speeds. This will encourage people to use private automobiles rather than other modes of travel (such as public transit). While travel times probably will not be reduced much in congested areas, many newly developing areas not affected by congestion will see an increase in motor-vehicle travel. Reduced travel times will also encourage increased low density development. Both of these will result in future increases in NOx emissions.
Increased speed limits on arterial roads (which many states are expected to implement) will also increase the risk of travel to both bicyclists and pedestrians. The impact will be to reduce the use of these environmentally beneficial modes.
Many states will, in fact, be required by their own speed limit statutes to increase speed limits on arterial roads. These speed limits are generally set by the 85th percentile rule. This specifies that speed limits must be set at the speed at which the 85th percentile of the traffic is moving. Higher freeway speeds are likely to induce drivers to travel at higher speeds on arterial roads (due to a decreased perception of their actual speed when leaving a freeway). This will force many states to increase existing speed limits on these arterials, if they intend to abide by their own statutes.
The only indirect impact that may somewhat reduce any increase in emissions is the higher cost of traveling at higher speeds, due to decreased fuel efficiency. This is not expected to be a major off-setting factor, due to the relatively low cost of gasoline.
References
FHWA, 1994; Federal Highway Administration, Highway Statistics 1993, Washington, DC 1994.
Pechan, 1992; E.H. Pechan & Associates, Sensitivity Analysis of MOBILE4.1 Emissions Factors, Prepared for EPA Ozone/Carbon Monoxide Programs Branch, Springfield, Virginia, July 1992.
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Speaking at a climate change conference in Miami, California Governor Arnold Scwarzenegger said drivers can do a lot to cut fuel costs by driving slower.
"Who can cut (costs) down is you, you, you and you," Schwarzenegger
said. "You can cut it down. Take your car, for instance. Go and get the
perfect tire pressure. Tune up your engine. Drive slower." He went on to say "energy prices are not going to go back to the good
old days" and it is "bogus" for politicians to promise otherwise."
"Politicians have been throwing around all kinds
of ideas in response to the skyrocketing energy prices, from the
rethinking of nuclear power to pushing biofuels and more renewables and
ending the ban on offshore drilling," Schwarzenegger said. "But anyone
who tells you this would bring down gas prices any time soon is blowing
smoke. I think that people should really be in charge of their
own destiny and how much they want to pay for fuel, not wait for the
politicians," he said.
The Drive 55 Conservation Project is delighted with the Governor's message and hand delivered a Thank You letter with Drive 55 bumper stickers to his office in Sacramento today. Leadership in the legislature also got a letter and some Drive 55 bumper stickers hand delivered to their offices in the Capital, inviting them to 'Lead by example'.
Quote sources:
Sacramento BEE
http://www.sacbee.com/111/story/1042081.html
LA Times
http://www.latimes.com/news/politics/
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