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Scientists are working on the development of alternative fuels such as biofuels or hydrogen, but these have their own limitations. For example, a significant amount of land area is required to produce crops for biofuels; if we converted every single acre of corn grown in the U.S. to ethanol, it would provide 10% of our transportation energy needs. Furthermore, growing crops for fuel rather than food has already sparked price increases and protests in less-developed countries around the world ( IMF, 2010 ). Is it fair to ask someone living on less then two dollars a day to pay half again as much for their food so we can drive wherever and whenever we want?

Emissions or outputs

The engine of the typical automobile or truck emits all sorts of noxious outputs. Some of them, including sulfur dioxides, carbon monoxide, and particulate matter, are directly harmful to humans; they irritate our lungs and make it hard for us to breathe. (Plants are damaged in much the same way). These emissions come from either impure fuel or incomplete burning of fuel within an engine. Other noxious outputs cause harm indirectly. Nitrous oxides (the stuff that makes smog look brown) from exhaust, for example, interact with oxygen in the presence of sunlight (which is why smog is worse in Los Angeles and Houston), and ozone also damages our lungs.

Carbon dioxide, another emission that causes harm indirectly, is the most prevalent greenhouse gas (GHG), and transportation accounts for 23% of the CO 2 generated in the U.S. This is more than residential, commercial, or industrial users, behind only electrical power generation ( DOE, 2009 ). Of course, as was explained above, transportation is a derived demand, so to say that transportation itself is generating carbon emissions is somewhat misleading. The distance between activities, the modes we choose to get between them, and the amount of stuff we consume and where it is manufactured, all contribute to that derived demand and must be addressed in order to reduce GHG emissions from transportation.

Social impacts

If the definition of sustainability includes meeting the needs of the present population as well as the future, our current transportation system is a failure. Within most of the U.S., lack of access to a personal automobile means greatly reduced travel or none at all. For people who are too young, too old, or physically unable to drive, this means asking others for rides, relying heavily on under-funded public transit systems, or simply not traveling. Consider, for example, how children in the U.S. travel to and from school. In 1970, about 50% of school-aged children walked or biked to school, but by 2001, that number had dropped to 15% ( Appleyard, 2005 ). At the same time that childhood obesity and diabetes are rising, children are getting less and less exercise, even something as simple as walking to school. Furthermore, parents dropping off their children at school can increase traffic levels by 20 to 25%, not just at the school itself, but also throughout the town in question ( Appleyard, 2005 ). At the other end of the age spectrum, elderly people may be functionally trapped in their homes if they are unable to drive and lack another means of getting to shopping, health care, social activities, etc. Finally, Hurricane Katrina made it clear that access to a car can actually be a matter of life or death: the evacuation of New Orleans worked very well for people with cars, but hundreds died because they didn't have the ability to drive away.

Questions & Answers

A golfer on a fairway is 70 m away from the green, which sits below the level of the fairway by 20 m. If the golfer hits the ball at an angle of 40° with an initial speed of 20 m/s, how close to the green does she come?
Aislinn Reply
cm
tijani
what is titration
John Reply
what is physics
Siyaka Reply
A mouse of mass 200 g falls 100 m down a vertical mine shaft and lands at the bottom with a speed of 8.0 m/s. During its fall, how much work is done on the mouse by air resistance
Jude Reply
Can you compute that for me. Ty
Jude
what is the dimension formula of energy?
David Reply
what is viscosity?
David
what is inorganic
emma Reply
what is chemistry
Youesf Reply
what is inorganic
emma
Chemistry is a branch of science that deals with the study of matter,it composition,it structure and the changes it undergoes
Adjei
please, I'm a physics student and I need help in physics
Adjanou
chemistry could also be understood like the sexual attraction/repulsion of the male and female elements. the reaction varies depending on the energy differences of each given gender. + masculine -female.
Pedro
A ball is thrown straight up.it passes a 2.0m high window 7.50 m off the ground on it path up and takes 1.30 s to go past the window.what was the ball initial velocity
Krampah Reply
2. A sled plus passenger with total mass 50 kg is pulled 20 m across the snow (0.20) at constant velocity by a force directed 25° above the horizontal. Calculate (a) the work of the applied force, (b) the work of friction, and (c) the total work.
Sahid Reply
you have been hired as an espert witness in a court case involving an automobile accident. the accident involved car A of mass 1500kg which crashed into stationary car B of mass 1100kg. the driver of car A applied his brakes 15 m before he skidded and crashed into car B. after the collision, car A s
Samuel Reply
can someone explain to me, an ignorant high school student, why the trend of the graph doesn't follow the fact that the higher frequency a sound wave is, the more power it is, hence, making me think the phons output would follow this general trend?
Joseph Reply
Nevermind i just realied that the graph is the phons output for a person with normal hearing and not just the phons output of the sound waves power, I should read the entire thing next time
Joseph
Follow up question, does anyone know where I can find a graph that accuretly depicts the actual relative "power" output of sound over its frequency instead of just humans hearing
Joseph
"Generation of electrical energy from sound energy | IEEE Conference Publication | IEEE Xplore" ***ieeexplore.ieee.org/document/7150687?reload=true
Ryan
what's motion
Maurice Reply
what are the types of wave
Maurice
answer
Magreth
progressive wave
Magreth
hello friend how are you
Muhammad Reply
fine, how about you?
Mohammed
hi
Mujahid
A string is 3.00 m long with a mass of 5.00 g. The string is held taut with a tension of 500.00 N applied to the string. A pulse is sent down the string. How long does it take the pulse to travel the 3.00 m of the string?
yasuo Reply
Who can show me the full solution in this problem?
Reofrir Reply
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Source:  OpenStax, Sustainability: a comprehensive foundation. OpenStax CNX. Nov 11, 2013 Download for free at http://legacy.cnx.org/content/col11325/1.43
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