Environmental Engineering Reference
In-Depth Information
hybrid cars. Savings can be made with a gasoline-powered vehicle by
proper maintenance, such as keeping the correct tire pressure, keeping
the odometer at 50 to 60 mph on open roads, and keeping the car
tuned up. In 2010 the government specifi ed that by 2016 auto fuel
effi ciency must be 35 miles per gallon, a 40 percent increase over
existing requirements.
Can the emissions from the tailpipes of private cars be stopped? Prob-
ably not completely, although the high cost of gasoline in 2008 and the
weak economy in 2008 and 2009 did reduce the number of miles most
Americans drove. A recent Harris poll showed that 92 percent of Ameri-
cans believe that gasoline prices will trend upward in the future, perhaps
indicating that the reduction in miles driven may be permanent.
But emissions certainly could be permanently reduced by an increase
in the availability of public transportation. At present, only 5 percent of
U.S. commuters take public transportation because most lack convenient
access.
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Fewer than 5 percent of Americans live within a half-mile of
light-rail transit, probably as far as most of us would walk. Only half of
Americans live within a quarter-mile of any public transportation. Nev-
ertheless, the number of passengers on public transportation has increased
steadily in recent years—25 percent between 1997 and 2007.
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Ridership
in 2007 and 2008 was the highest in fi fty years, and 2008 saw a 4 percent
increase over 2007.
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More than 300 metropolitan areas experienced an
increase in public transit between 2007 and 2008 as gasoline prices
soared. If public transportation were more easily available, there is a
strong possibility that ridership would increase. Bus and rail offi cials say
support for public transport goes beyond the increase in ridership. On
election day in 2008, voters around the country passed twenty-fi ve of
thirty-three ballot initiatives to increase local and state taxes for public
transportation.
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When people vote to increase their taxes, they are
serious about an issue.
There is one form of public transportation that is not benefi cial to the
environment, commercial aviation, and air traffi c is expected to double
between 1997 and 2017. Jet fuel accounts for 10 percent of America's
fuel consumption. A jumbo jet burns 3,250 gallons of this refi ned hydro-
carbon per hour of fl ight, spewing large amounts of greenhouse gas
pollutants into the atmosphere. And thousands of commercial aircraft
are fl ying every day. Commercial aircraft currently generate 3.5 percent
of greenhouse gas emissions.
Oceangoing ships are polluters as well. As international trade has
exploded and shipping capacity has grown by 50 percent, cargo ships
