Environmental benefits of a national 55 MPH speed limit
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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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Analysis of the Effects of Eliminating the National Speed Limit on NOx Emissions |
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This report was prepared by E. H. Pechan and Associates for the
U.S. Environmental Protection Agency, Office of Policy, Planning,
and Evaluation. For further information, please contact Bob Noland
at 202-260-2418.
Analysis of the Effects of Eliminating the National
Speed Limit on NOx Emissions
Introduction
Highway vehicles contribute approximately one third of the oxides of
nitrogen (NOx) emissions released to the atmosphere in the United States
annually (EPA, 1994). Since highway vehicles contribute such a large
percentage of NOx emissions, proposed modifications in the National
Highway System bill are examined in this analysis to determine their
effect on this important source category. Specifically, the U.S. Senate
has recently proposed to abolish the national maximum speed limit. Such
a policy modification may have a significant impact on the magnitude of
NOx emissions from motor vehicles. Motor vehicle NOx emissions result
from combustion processes and tend to increase with increasing speeds
above 48 miles per hour (mph) (Pechan, 1992). This analysis examines
the potential consequences of the proposed Senate changes to the
National Highway System bill on highway vehicle NOx emission levels. The
Senate recently voted to repeal the national maximum speed limit on
federally financed highways. The national maximum speed limit rule
currently restricts vehicle speed limits to 65 mph on rural freeways,
and 55 mph for all other corridors. The Senate proposal to repeal the
national speed limit passed on June 19, 1995 with the stipulation that
federal speed limits still apply to commercial vehicles such as trucks
and buses. If the bill passes through the House of Representatives,
States would have the authority to determine the maximum allowable speed
limits for automobiles within their State boundaries. Trucks and buses
would still be subject to the 55 mph urban and 65 mph rural limits. The
national maximum speed limit was established in 1974; it restricted
speed limits to 55 mph. The impetus for this regulation was to conserve
fuel during the 1973 oil embargo and subsequent energy crisis. Prior to
the national limit, States determined speed limits for all corridors
within their jurisdictions. Table 1 presents the speed limits
maintained by States in January 1973, prior to implementation of the
national maximum speed limit. Also presented in Table 1 are current
speed limits for automobiles and trucks, by State. In 1987, the maximum
speed limit on rural freeways was increased to 65 mph. Rural freeways
are defined as freeways located in designated "rural" areas,
with a population less than 50,000. Freeways are "controlled
access facilities" which means that access is by ramp only and
freeways are divided highways which usually consist of four lanes. The
likely effect of the recent Senate proposal abolishing the national
speed limit will be increases in rural freeway speed limits for
automobiles. Since most States adhered to the 55 mph speed limit in
urban areas before the national maximum speed limit was established,
changes in speed limits around metropolitan areas are expected to be
minimal (FHWA, 1995). As shown in Table 1, speed limits on rural
freeways before the national maximum limit of 65 mph did not exceed 75
mph, with the exception of Montana and Nevada -- which did not establish
maximum limits. Most maximum speed limits for rural corridors ranged
between 65 and 75 mph with the majority of States setting rural speed
limits of 70 mph.
This analysis assumes that States are most likely to raise the maximum
speed limits on their rural freeways to limits established prior to the
national maximum speed limit and retain the 55 mph limit in urban areas. |
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Read more...
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Emissions Impact of Elimination of the National 55 mph Speed Limit |
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Related documents:
ENVSPOMS.TXT (this 1/8/96 OMS memo)
ENVSPMEM.TXT (11/30/95 OPPE memo)
ENV-SPDS.TXT or ENV-SPDS.W51 (E.H. Pechan report:
Analysis of the Effects of Eliminating the National
Speed Limit on NOx Emissions)
For further information on this issue, please contact:
Bob Noland, EPA/OPPE 202-260-2418.
Laura Gottsman, EPA/OPPE 202-260-9247
Will Schroeer, EPA/OPPE 202-260-1126
Terry Newell, EPA/OMS 313-668-4462
01.08.96
Information from the EPA Office of Mobile Sources:
Emissions Impact of Elimination of the National 55 mph Speed Limit
President Clinton recently signed into law a bill that includes
a provision eliminating 55/65 mph speed limits as a prerequisite
for Federal highway funding.[1] Several States have already acted
to increase speed limits on limited-access highways, and others
are considering such action. This has led to questions
concerning the emissions impact of elimination of the national
speed limit. This statement provides an initial look at those
impacts, and discusses activity in progress at EPA to better
quantify those impacts.
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Drive 55 KTLK Radio Interview |
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October 31 radio interview with Marc Germain on Los Angeles radio station KTLK 1150AM. Click Read More to listen. |
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Ideas to reduce GHG emmissions submitted to CARB |
In response to the California Air Resources Board solicitation for ideas to reduce greenhouse gas emissions, October 1, 2007 the Drive 55 Conservation Project submitted these three pdf files offering our ideas to reduce greenhouse gas emissions. The files are named as follows:
Sept_2007_reduce_GHG.pdf (application/pdf) 88kb
Drive 55 Conservation Project Action Plan.pdf (application/pdf) 121kb
Emissions Impact of Elimination of the National 55 mph Speed Limit.pdf (application/pdf) 101kb
View all the submissions here.
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We need your help to contact these organizations, urging them to endorse the Drive 55 Conservation Project. Please look over the list below, and if you find you are a member or supporter of any of them, take a few minutes to send a letter or e-mail asking them to endorse the Drive 55 Conservation Project. If they hear from you it will help them to have confidence there is public support and encourage their endorsement.
Thank you in advance for your care and concern for this fragile environment we all share. |
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