Design Life-Cycle

Tania Renteria

13 March 2014

DES 40a

Winter 2014

The Street Sign - Raw Materials

INTRO

The design of street signs really revolutionized new ways of communication transportation and urbanization of many cities. The creation of retroflectives and new material us such as aluminum also took the street sign industry to a new level of aesthetic and revolutionary importance. Although street signs are everywhere nowadays there a whole process that occurs behind the scenes and literally starts from the ground up. Many people only consider the end result or the actual final used on a regular day basis, but it is also very important to consider the production and energy behind everything that we use and see around us that has been created. Raw materials are rarely though of when thinking of a life cycle because a lot of the time we life cycles start with materials that have already been humanly enhanced or reduced. A lot of people consider primary and secondary materials to be raw materials when in reality there is another world behind even the most basic elements that are used to produce many of the products we use today. One must remember that everything around use once was part of our earth or was inspired by something that naturally came from our earth, and from that we start to build a structure of how regular day objects are created. As for street sings, we will also use this process of cradle to cradle to learn the process and the raw earth materials that go into street sign life cycle.

MATERIALS

There are two main parts or elements that go into the production of street signs. The major and most abundant component of a street sing is the aluminum blanks, which give the signs their shape, texture and durability. The other major component is the retroflective sheeting, which created the graphics or backgrounds to almost all street signs used today.  Although these two parts function as the framework to a street sign, there is a long process that takes place before we arrive at aluminum blanks and retroflective. That process is critical to the production infrastructure.

RAW MATERIALS

Raw materials are materials that are pure mixtures of minerals and other compounds that come straight from the earth. The different between a raw material and other materials that seem to be raw materials is that they have not been changed in any chemical/physical way. These materials are raw from the earth and have not been enhanced in any sort of way.

Retroflectives are one of the last new components that were added to the street signs that we see today but they were quickly adapted because of their importance. If we look at earlier times when street signs were being developed they were usually made from wood or steel and had no retroflective parts. Retroflective parts are now so important, and used in almost all road signs that they are regulated by the government to have a certain amount reflective. Retroflectives help illuminate street names, milage and important information which otherwise would not be visible from longer distances. Most people look at the major parts of sign and realize that these retroflective parts are made from retroflective tape/ sheeting but it goes way beyond that. Retroflective tape is made from small glass beads, which are consequently made out of glass. Making glass is a hard and long process and therefore creates a long process to be able to make beads and eventually retroflective materials which shows how much work goes into something that looks so simple.

The production of glass first starts with lighting striking sand, which creates quartz. Quartz are commonly found in nature and are largest and the raw form of silica, which is the key component to making glass. In order to get pure silica the iron impurities, which are in the quartz, are usually filtered after being retrieved from the ground. Once the minerals are separated out you can get Silica or silicon dioxide (SiO2). Silica alone is not the only compounded needed to make glass. Silica has some qualities that make it hard to create glass from pure silica. Silica is usually very soluble in water and has an extremely high melting point. Therefore, in order to lower the melting point of silica other minerals such as alkali soda are added to create a mixture.

 Once mixed these compounds are finally melted down with a high temperature of 2,500 degrees Fahrenheit. When melted the silica mixture turns into an orange liquid, which can then be dried, molded or rolled into glass. Glass beads are also made at this point  of the cycle. They are made into small specs of glass, which are then used for the retroflectives in sings.

 The first sings that were ever made with retroflectives, the glass beads were directly placed on the signs over some adhesive. The problem with that process is that it created a build up of dirt that was collected in between the glass beads that made sings hard to read and made them less durable. In order to keep that from happening now there is retroflectives sheeting which places a thin transparent film over the glass beads that helps keep all the glass beads together and prevents wear and tear and all together makes the retroreflective graphics more durable. An addition of resin base and retroflective coats also enhanced the durability of the retroflectives that went onto the production of the retroflective sheets. 1

Newer retroflective sheets and reflective tape are also now made with microprisms. Instead of using glass beads they create a reflection of light that diverts the microprisms are angled so that they can reflect the light a certain direction. These microprisms were designed so that the light being reflected from a source would be reflected right ack, giving it the outmost potential of reflection. When using a glass bead, the beads are circular and can reflect like in all sorts of directions, but with microprisms they can control the direction of the light being reflected. The microprism have been engineered so that the sharp corners can reflect the light to the source and give optimal reflection. Most sign productions are starting to use microprism because it creates bigger reflection even in the daylight.

Once the sheeting has been created, the graphics for signs such as letters or pictograms can be created for sings and are sometimes even used for other materials such as articles of clothing or retroflectives for bicycles. The graphics come into play once the retroflective sheeting has been processed and sent out to companies that create the actual street signs. But before we get to that process we need another major component to create the sing. The second but very important and major part of the sign, the infrastructure that is made with aluminum blanks

The body of signs, or blanks, are made from aluminum. 2 Aluminum is not a raw material but  is made from a substance called bauxite which is a raw material that comes straight from the earth and is at its rawest form as a clay like soil. Bauxite is  easily mined from the ground and once gathered can begin the process of turning into aluminum . After extraction from the earth bauxite is taken to plants where the Bauxite can be cleaned away from the clay, and once separated can be grinded down into a smaller pieces. While bauxite is grinded down, alumina can be extracted from the mixture through the process of refining. The refining process is the process of cleaning and separating the chemicals with the use of lime and caustic soda. From there the mixture is heated, filtered and dried until alumina becomes a white powdery substance. Following that process the pure alumina must be mixed with two other raw materials carbon and aluminum oxide, which also require the use of electricity. In order to make liquid aluminum electricity is ran through a positive and a negative carbon based cathode and anode, which react with the oxygen that is in the alumina and then consequently produces carbon dioxide which then creates the liquid aluminum which can now be casted into many different things but for the case of the street signs would be rolling. Aluminums is very water resistant and very malleable, which means it can be constructed into sheets that can be sued to make durable products, such as street signs.

Aluminum is also preferred over other materials because it is a very light metal (about one-third or steel). Another advantage of using aluminum is that it is very durable and matches the strength of steel. Another reason why aluminum has been chosen as the main material for street sings is that aluminum by itself is also very reflective and is very beneficial for street signs. Aluminum is also very prone to rusting because it does not contain corrosion, which is common in iron and steel. With all these benefits of aluminum one can see why it has been preferred over other metals. 

Another important but material that people forget about is the electricity. When reading through some of the data on the production of aluminum 3  there was a statement that mentioned electricity as a raw material. There is little truth to that electricity is used in the process of making materials such as aluminum and is also used on the kinetic process which is put into the machinery process. Electricity by itself is not a raw material because it is not at its simplest form. Electricity is achieved from the burning of different raw materials.

Most of the machines used to cut the aluminum planks and adhesive run through electricity. Therefore a source of electrical energy is required to make street signs.  4 The cheapest way to make electricity is by coal and is used to make around 44.9% of all electricity in the United States. Coal comes from peat, which is a material made from decayed of organic matter and vegetation for over thousands of years and has settled in deposits in the earth. The peat hardens over a very long time and produces coal, which is a fossil fuel and can be burned to create energy which converts into electricity. Electricity can also be made form nuclear power, hydroelectric power and other renewable resources, but those do not compare to the amount of coal and fossil fuels we burn to convert to electricity.

PRODUCTION

Once you have the retroflective sheeting and aluminum sheeting the production of actual street signs can finally begin.  Factories usually purchase the retroflective and aluminum from other companies and they bring them to their production factory to put all of the materials together and create the final product, a street sign. 5 The first big step is creating the aluminum blanks that are made from the aluminum sheets. The aluminum sheets are cut by a bandsaw, which replicates the same precise cut onto many sheets. Then with the use of a punch press, if needed the corners of the sign can be rounded and the holes for the bolts that will later be holding the sign up. Once the blanks are made the aluminum blanks are laminated with the retroflective sheeting which comes in all sorts of colors and are different for different street sign designs.  The lettering on the signs can be added by silk screening or by adhesive retroflective it just depends on whether you want the lettering to also be reflective or just plain. The final sings are then taken into an oven like machine that heats up and dries the signs at 107 Celsius. There the sings sit for a few minutes or more depending on the colors you use. Once they come out of the oven the signs are ready to be placed on the streets.

Through the production there is no introduction of raw materials to any of the actual parts of the street sing. There are more primary materials such as electricity that is used for the use of the different machines in the production process. Heat is also used in for the final last step of the signs, and it’s used for the purpose of solidifying all of the elements of the sign.

ENERGY

A lot of the energy that is used to convert the raw materials into usable materials for the street signs is through the use of thermal energy. Since the minerals are raw and coming straight from the earth they are usually still in rock form or some other type of sediment. In order to make it into a material that is malleable and useful we have to purify it from other minerals that the material was in contact with. With thermal energy minerals are usually dissolved at very high temperatures and can be purified and then mixed with the necessary other elements to make the primary materials needed for production.

Once those materials are made there is an increase use of kinetic energy that drives the forces for the production of street sings. From the cutting of machine to even hand cutting some of the retroflectives a lot kinetic energy is used to make street sings.

EMISSION AND WASTE

6 Most of the raw materials create other mineral waste. Although it is being very vastly studied, scientists are trying to create a way that these wasted minerals can be reused. As discussed in this research there has to be a way to be able to have a separation process where the alkali from aluminum and other minerals can be successfully separated and reused for other purposes, but also be used as a raw material. Until now the minerals that come off the processing are just waste.

Sings are hard to recycle because they are so durable they are usually only taken down if they are really damaged from environmental factors.  Unless signs seem not to be too badly damaged then they can go through hydro blasting and repurposing

Conclusion:

While researching, it was hard to figure out what kind of energy is used for what because of the many different processed that signs can go through. When researching I found that there are many ways to do just one thing and that it is not easy to synchronize your information there are so many ways of getting the same result. And although some companies are uniformed and use similar methods there are smaller production factories that use entire different ways to create a sing.

It was interesting to find that signs don’t necessarily have one company that provide signs all around the US, I found that some cities have their own small production companies and that’s why the processes vary so much. The most important thing that I took away from my research what that it took time and energy to find the raw materials necessary to make the things we have today. Aluminum is used for so many things around us and it is very interesting to think that these objects came from the ground.

Bibliography

Advamed, Inc. http://www.madehow.com/Volume-2/Road-Sign.html#b. 2014.

Division of Artifax Displays Inc. http://glasstopsdirect.com/news/how-is-glass-made.html.

Freudiger, Michael.Making Road Signs.https://www.youtube.com/watch?v=OPMqXNyLLWE. April 9, 2007.

International Associaion of Certified Home Inspectors Inc. http://www.nachi.org/electricity-origin-consumption-cost.htm. 2006-2014.

Kashcheev, I. D., Byandina T. V.Refractories and Industrial Ceramics. http://link.springer.com/article/10.1007%2Fs11148-008-9049-8#page-1. June, 2008.

Moeur, Richard C. http://www.trafficsign.us/signsheet.html. Copyright 2010.

Norsk Hyro ASA. http://www.hydro.com/en/About-aluminium/How-its-made/. 2014.

Norsk Hyro ASA. http://www.hydro.com/en/About-aluminium/How-its-made/. 2014.

Roland, William P. Retroreflective Microprism Sheeting. http://www.google.com/patents/US5376431.  December 29, 1994.

 1  Roland, William P. Retroreflective Microprism Sheeting. http://www.google.com/patents/US5376431.  December 29, 1994.

 2  Norsk Hyro ASA. http://www.hydro.com/en/About-aluminium/How-its-made/. 2014.

 3  Norsk Hyro ASA. http://www.hydro.com/en/About-aluminium/How-its-made/. 2014.

 4  International Associaion of Certified Home Inspectors Inc. http://www.nachi.org/electricity-origin-consumption-cost.htm. 2006-2014.

 5  Freudiger, Michael.Making Road Signs.https://www.youtube.com/watch?v=OPMqXNyLLWE. April 9, 2007.

 6  Kashcheev, I. D., Byandina T. V.Refractories and Industrial Ceramics. http://link.springer.com/article/10.1007%2Fs11148-008-9049-8#page-1. June, 2008.

Shayda Rashidi

DES 40A

Research Paper

Embodied Energy

The Production and Embodied Energy in Making Road Signs

Its thin simplistic appearance would fool many into thinking the energy process of road sign production is quiet melancholy. Research shows that contrary to common belief, the embodied energy invested in making road signs is in fact an energy-intensive process throughout the majority of its life cycle. From the extraction of raw materials to the finalized product of a road sign, energy is a necessity in almost every step. The energy placed into making road signs embodies a large scope of varying energy sources such as kinetic, chemical, electrical, and thermal energy. Though some materials, such as the aluminum, used in road sign production has the potential to be reused, the majority of the life cycle requires a significant amount of energy power from nonrenewable primary fuels.

The process of investigation on this research reveals the unethical realities of production of design, specifically road signs. The fact that much of the specifics regarding the consumption of energy during production were left undiscovered and difficult to obtain, brings to light the concerns common people should have in products that so influentially affect their daily lives. Why is so much information kept hidden regarding manufacturing processes of large production items? The embodied energy that goes into producing a single road sign can have a long-term consequence on the primary energy our society will be able to rely upon.

The Production and Embodied Energy in Retroreflective Sheeting

 A big factor that makes road signs for what they are is the ability to reflect. It is the reflective quality of signs, especially during dark hours, that give road signs their distinctive quality. Retroreflective sheeting are made of tiny glass beads, commonly known as quartz, that are then glued next to each other to create a sheet like presence. The energy in making retroreflective glass is a process that begins with the mining of sand. During this process, large machinery extract sand for further processing of quartz and later glass. This within itself is a very high- energy intensive process requiring primary energy in order to provide secondary energy.

The standard machineries used for sand extraction are cranes. Cranes typically need a 500-800 kW generator in order to lift the raw material of sand. During the dropping of the container, however, much of the energy is lost as wasted heat (Treacy). This is not taking into account the total sum of diesel fuel needed for the crane generators. The weight of the crane should be accounted for when calculating the energy consumption just in the initial process of mining raw materials for the production of road signs.

The mining of sand is then lead by the production and making of encapsulated glass beads. The common type of retroreflective sheeting used specifically for road signs is called Type III sheeting. Type III sheeting is made from a translucent pigment layer and inner reflective layer faced with glass beads, then lattice connects the two layers (Llyod). Though little information was found on the actual making of the sheeting itself, details on the retroreflective sheeting production reveal that varying types of energy source is required.

There are only a few companies known to provide rolls of sheeting to sign shops, 3M being one of the top providers. According to 3M’s conditions, manufacturing retroreflective material require temperature conditions within factories between an optimum range of 180-220°c. Without these conditions, retroreflective sheeting is more bound to become unworkable and unusable in its design purpose (3M Production Standards Manual for the Manufacture of Permanent Prismatic Road Signs."). This means that manufacturing is almost constantly utilizing energy input of heating and cooling systems, a high and intensive reliance on electrical energy.

Through the entirety of retroreflective sheeting manufacturing process, some form of machinery is required. From the cutting of sheets to the application of sign blanks, energy is a constant factor in each step. Prepared for cutting, retroreflective sheeting are stacked and placed under a wallboard where the appropriate shape is cut using a band saw machine ("How Products Are Made").  

From the band saw, the retroreflective sheeting goes through other various processes including clicker press, lamination, and run through a roller for the removal of air bubbles. It was at this point of the research finding information on machinery specification was minimal, and large educated assumptions are made based upon the examination of old and outdated manuals. It is assumed that large manufacturing machinery require notable amount of electricity, ranging from 200 to 600 volts. It is important to note, however, that there is a heavy reliance of kinetic energy from people throughout the process. Unlike many other manufacturing, signs require a great deal of assistance of energy from people, in which much of the process transitions could not be done without the assistance of workers.

The Production and Embodied Energy in Aluminum Blank Processing

Aluminum plays a key role in Road Signs. In fact, aluminum sheeting, called blanks, is like the signs body. Without the blank, the road sign would be lifeless. Untouched blanks, blanks with no addition of retroreflective sheeting, are almost entirely recyclable.  Blanks on their own can be melted, reused, and repurposed. Unfortunately, because road signs do require retroreflective sheeting or other forms of screening, the blank itself becomes nonrenewable, making the production process of blanks a very high intensive energy consumption.

In the United States, aluminum production is executed in two ways—primary production and secondary production. Approaching aluminum production with primary means entails raw materials and ingots. This process alone is very electrically intensive ("U.S. Energy Information Administration - EIA - Independent Statistics and Analysis").  It is with secondary production that much of the energy is conserved and how aluminum production can become more “green.” This is because with secondary production, scraps of used aluminum are being used and smelted to develop new aluminum products ("U.S. Energy Information Administration - EIA - Independent Statistics and Analysis"). In 2006, the average energy consumption for the entire aluminum sector accounted for over 300 trillion British thermal units (EIA). A British thermal unit is a conventional unit of energy equivalent to 1055 joules. One ton of pure aluminum material requires about 200 million British thermal units. This is 7 times more energy needed to make one ton of steel. According to Streamline, it actually takes about 200 million BTUs to make one ton of pure aluminum material, which is 7 times the amount of energy that is required for making just one ton of new steel. With such numbers, it is no mystery that aluminum production requires an abundance of energy, so much so that an average of 2,600 Megawatts are used in among aluminum factory (Streamline).

Bauxite ore is the beginning of primary production. Extraction of bauxite often takes places in Jamaica and South America (EIA). After bauxite has been transferred to production sites in the United States, alumina processing occurs followed by smelting (EIA). Alumina production is high in energy consumption, as a large sum is required to produce it. Alunorte, the world’s largest alumina refinery, “has a total production capacity of almost 6.3 million metric tons per year, which is about 7 percent of the world’s production,” using their coal and heavy fuel oil as their main supply of electricity and steam generation (“About Aluminum”). In order to produce aluminum metal from alumina, oxygen bonds must be broken using electrolysis, and thus resulting with liquid aluminum. “Roughly 14 kilowatt hours of electricity are required to produce 1 kilogram of aluminum. That’s as much power as 30 TV sets use in one hour” (“About Aluminum”).

Once the aluminum sheeting has been acquired, sign factories go through the process of cutting the blanks, examination of the blanks, and degreasing the blanks. Similar to the sheeting, the blanks are placed into the band saw machinery or metal shear machinery to cut out its specific shape and drilled for later installation. It is also assumed, based on the model manual for BP-5060 shear machinery, that average power consumption is about 6kW. After cutting the blanks, they are checked by workers for any defects and cleaned of any grime. “The blank is then degreased by immersion in a bath of trichloroethylene or percholorethylene vapor. Certain alkaline solutions can be used instead of the vapors in the bath” (How Products are Made”). No information could be found as to how the chemical bath was maintained, if it was powered by electrical sources, or how the workers immerse the blanks. It is thus assumed that there is an extensive amount of chemical energy in the vapor process, as it is referred to as bath. Furthermore, it is also noted that a great deal of energy is lost to the waste of the chemical baths, as it cannot be reused or recycled.

The Road Sign

At last, the retroreflective sheeting and the blank meet. Prior to being stored and sent out for outside use, the road sign production embark on a few more processes, which include application of the sheeting and heating of the sign. During the process of applying the reflective sheeting to the blank, a squeeze-roller applicator is utilized. An applicator requires electrical energy input, a common secondary energy source. The typical applicator requires about 220V. Not only does the applicator require electrical energy, but also produces heat at around 120°F, which means that thermal energy is also lost in the open space of the factory. After the sign has been cranked through the applicator to remove air bubbles, it is then transferred to the heat lamp vacuum applicator. The heat lamp vacuum applicator lamp bank contains 35 infrared lamps, each requiring 375 watts of electrical energy. Installation power alone requires 460V. Furthermore, none of these machines are to be operated on without worker supervision, thus always needing an operator for the machinery. Once the sign has been heated, it is cooled, and heated once more before the completion of the sign and ready for use.

Despite the rarity, road signs have the potential to conserve and recycle more energy. Sign recyclers sustain the life cycle of road signs by furthering its use. Signs that have been outdated and weathered are taken in, cleaned, and reused. Many companies accomplish this by hydrostriping old laminates on aluminum blanks. The blanks are then once more refaced and placed back into service among the streets (Street Division). It is when the retroreflective sheeting cannot removed that the aluminum cannot be repurposed. Since retroreflective sheeting goes through a chemical process for perseveration, not all blanks can be reused. In order to recycle aluminum, any preexisting material must be removed. Though the overall average production of road signs is executed using the primary production, there is still some effort being made by major companies to reduce the use of energy. According to 3M, a major supplier of the sheeting rolls, effort has been made to use “greener” forms of energy supply to help reduce the release of greenhouse gases. Since 2001, 3M have used alternative energy from purchased wind energy based in a facility in Austin, Texas; 30% of their energy use is from wind. Furthermore, cities also partake in the attempts of reducing energy use by upcycling the aluminum blanks, and even having them refaced and re-serviced.

Prior to research, road signs never came across as this complex process, much less a life cycle. It was always only looked at as its final finish. Having done this research, it has become undoubtedly evident that a road sign is not just a product, yet rather an extensive process that begins with the raw material and both primary and secondary energy along with it. It is extraordinary to discover so much use in energy consumption, yet a great deal to still to be uncovered. What seemed once so simple is now an intricate and intensive embodiment of energy in the production of road signs.

 Works Cited 

3M. Heat-Lamp Vacuum Applicator. N.p.: 3M, n.d. Welcome to PMBlack Co. Web. 1 Mar. 2014. <http://pmblackco.com/>.

"3M Production Standards Manual for the Manufacture of Permanent Prismatic Road Signs." 3M Production Standards Manual for Permanent Prismatic Signs. 3M, n.d. Web <https://solutions.3m.com/3MContentRetrievalAPI/BlobServlet?lmd=1371055889000&locale=en_GB&assetType=MMM_Image&assetId=1361623982260&blobAttribute=ImageFile>.

"About Aluminium." Hydro. Norsk Hydro ASA, n.d. Web. 1 Mar. 2014. <http://www.hydro.com/en/About-aluminium/>.

The Aluminum Association. "News & Statistics." Aluminum. The Aluminum Association, 2008. Web. 1 Mar. 2014 <http://www.aluminum.org/AM/Template.cfm?Section=News_Statistics>.

"Climate Change." 3M. 3M, n.d. Web. 1 Mar. 2014.   <http://solutions.3m.com/wps/portal/3M/en_US/3MSustainability/Global/Environment/ClimateChange/. 

"How Products Are Made." How Road Sign Is Made. N.p., n.d. Web. 28 Feb. 2014. http://www.madehow.com/Volume-2/Road-Sign.html#b

Llyod, John. "A Brief History of Retroreflective Sign Face Sheet Materials." A Brief History of Retroreflective Sign Face Sheet Materials. John Lloyd, 2008. Web. 1 Mar. 2014. <http://webcache.googleusercontent.com/search?q=cache:kw_8gNilmbgJ:www.rema.org.uk/pub/pdf/history-retroreflective-materials.pdf+&cd=10&hl=en&ct=clnk&gl=us>.

Liu, Gang, and Daniel Muller. "Addressing Sustainability in the Aluminum Industry: A Critical Review of Life Cycle Assessments." Journal of Cleaner Production 35 (2012): 108-17. Web. 1 Mar. 2014.

Mardikar, Yogesh. Establishing Baseline Electrical Energy Consumption in Wood Processing Sawmills: A Model Based on Energy Analysis and Diagnostics. N.p.: n.p., 2007. Web. <http://books.google.com/books?id=yX_UrgPZmd4C&printsec=frontcover#v=twopage&q&f=false>.

Moeur, Richard C. "Retroreflective Sheetings Used for Sign Faces." Manual of Traffic Signs. Richard C. Moeur., 15 Sept. 2010. Web. 1 Mar. 2014. <http://www.trafficsign.us/signsheet.html>.

"Recycling Service Transforms Aluminum Road Signs." Green Manufacturer. FMA Communications, Inc., 1 Aug. 2013. Web. 1 Mar. 2014. <http://www.greenmanufacturer.net/product/materials/recycling-service-transforms-aluminum-road-signs>.

Streamline. "Aluminum: How Sustainable Is It?" Streamline. Streamline, 2010. Web. 12 Mar. 2013. <http://www.streamlinemr.com/articles/aluminum-how-sustainable-is-it>.

Street Division. City of San Diego, n.d. Web. 1 Mar. 2014.

<https://www.sandiego.gov/street-div/services/trafficcontrol/traffic.shtml>.

 Treacy, Megean. "Energy-harvesting Cranes Cut Down on Fuel Used at Ports." Energy-harvesting Cranes Cut Down on Fuel Used at Ports. N.p., 8 Dec. 09. Web. 1 Mar. 2014. <http://www.ecogeek.org/preventing-pollution/2905-energy-harvesting-cranes-cut-down-on-fuel-used-at->.

EIA." Energy Needed to Produce Aluminum.” U.S. Department of Energy, n.d. Web. 1 Mar. 2014. <http://www.eia.gov/todayinenergy/detail.cfm?id=7570>.