Sustainable transportation refers to not only vehicles, but also includes fuels, infrastructure to deliver distribute these fuels (pipelines, stations), road networks and railways. Assessment of the transportation system needs to address the system effectiveness to meet society needs and environmental load associated with employed vehicles and infrastructures. This lesson overviews three important topics: alternative fuels and their associated impacts, zero-emission vehicles and status of electric vehicle technologies, and perspectives of the mass transit in sustainable community.
By the end of this lesson, you should be able to:
Report: Boutwell, M., Hackett, D.J., Soares, M.L., Petroleum and Renewable Fuel Supply Chain [1], Stillwater Associates, 2014.
Book: National Research Council. Transitions to Alternative Vehicles and Fuels. Washington, DC: The National Academies Press, 2013. Sections 2.5 and 2.6.
Web article: Penalosa, E., Role of Transport in Urban Development Policy [2], Federal Ministry for Economic Cooperation and Development, 2005.
If you have any questions while working through this Lesson, please post them to our Message Board forum in Canvas. You can use that space any time to chat about course topics or to ask questions. While you are there, please feel free to post your own responses if you are able to help out a classmate.
Let us start with some facts (Source: Sierra Club, 2014):
While the demand for transportation fuels is increasing, the continuing dependency of the U.S. economy on the foreign oil has put the country in an extremely vulnerable position with respect to meeting its transportation energy needs. This vulnerability is the critical motivator in searching for alternative fuels for vehicles and looking for alternative types of transportation as well. Sustainability of transportation basically means the flexibility and ability to provide for your own needs using the resources that are local, widely available, or renewable. What are the options there?
A number of alternatives (including both liquid and gaseous transportation fuels) have been a subject of research and implementation for the last few decades. Let us review the background behind those options. Click on the following links to read about the various classes of alternative fuels considered for transportation purposes:
All of the alternative fuels have their current advantages and disadvantages, which are briefly summarized in US DOE Data Table [10] (U.S. DOE, 2007).
Please note, the second row of this table shows an important metric used to characterize fuels (not only transportation fuels) - energy content or energy density. It is measured in energy units per unit volume or unit mass of the fuel. For example, from the data in the table, we can see that diesel and biodiesel fuels provide the highest amount of energy compared to other liquid fuels.
Viability of certain types of transportation fuels is closely related to the processing, supply, and distribution infrastructure. This is especially critical in the U.S. society and economy, which are heavily reliant on the usage of road vehicles for personal and industrial needs.
The following reading will introduce you to the strategies and facts associated to the transportation liquid fuel supply chains. This covers both existing renewable and non-renewable fuel infrastructures:
Report: Boutwell, M., Hackett, D.J., Soares, M.L., Petroleum and Renewable Fuel Supply Chain [1], Stillwater Associates, 2014.
While reading, try to find answers to the following self-study questions:
Strong motivators for developing alternative vehicle technologies and fuels are growing emissions and alarming urban air pollution levels. According to US EPA, in 2017, CO2 emissions from transportation sector surpassed the long-time leader – electric power sector – in the total national emissions budget. This change in “leadership” in part happened due to increasing addition of natural gas and renewable sources to the power generation mix while retiring older coal power plants in a number of states. Here is how the last half-decade of CO2 data looks like:
It is also estimated by EPA that nearly 60% of those transportations emissions in the United States come from passenger vehicles – cars, SUVs, and pickup trucks. There are economic reasons for that growth. In the late 2000s, the automobile emissions were moderated by the policies adopted by the Obama administration, which limited the amounts of gasoline the vehicles were supposed to use per mile. The Trump administration initially aimed at elimination of those fuel efficiency standards, which would most likely push future transportation emissions up. However, the proposal was recently revised, and after receiving comments from industry and public, the government did not eliminate the Obama standards, but adjusted them, to enforce only 1.5% annual MPG increase for passenger vehicles (as opposed to 5% under Obama regulation). The main argument for this change was that less stringent standards would make new cars more affordable, and thus increase driving safety for the families who would be otherwise be forced to drive older cars (USA Today [11]).
Low gas prices have also been contributing to the trend, tempting Americans to drive more miles and purchase larger personal vehicles (SUVs and such), which typically have lower gas mileage.
Click on the image to access the interactive map showing the transportation emissions in America. Mouse over a city area to display the emission metrics. Note the difference between the total emissions and emissions per person. While New York City leads the way among US cities in total emissions, if those emissions are normalized by population, contribution per person appears rather moderate (Popovich and Lu, 2019).
From these data, we see two drivers behind increasing emissions: population growth in metropolitan areas and increasing time behind the wheel. Some areas do better than others in terms of limiting driving through encouraging alternative mobility options. One example is DC Metro area, which shows the drop in emissions per person. In spite of increasing total population and total emissions, people appear to drive less than in other urban regions with high reliance on suburban commute.
Curbing vehicle emissions will require several factors working in synch: more efficient cars, developing alternative engine technologies (e.g., electric, hydrogen, natural gas), and changing in human lifestyle. Cities and states look for expanding transit options, such as rail, bus, and subway services, as well as encouraging carpooling and vehicle sharing programs. It is also anticipated that in 2021, New York will become the first city in the US to adopt a congestion pricing plan [13] to discourage drivers from entering the busiest areas of the city.
The concept of zero-emission vehicles is typically attributed to the transportation options that do not result in any harmful emissions during vehicle operation. Harmful emissions are defined as those known to have a negative impact on the environment or human health. They can include carbon dioxide, carbon monoxide, nitrogen and sulfur oxides, ozone, various hydrocarbons, volatile organic compounds (VOC), heavy metals in volatile forms (e.g., lead, mercury, etc.), and particulate matter.
Typical examples of zero-emission vehicles are electric (battery-powered) cars, electric trains, hydrogen-fueled vehicles, and human / animal powered transportation (e.g., bicycles, velomobiles, carriages, etc.). The battery technology for electric vehicles is based on charge/discharge cycles, meaning that the battery is charged beforehand using an electricity source and is discharged during vehicle operation. Because electricity production may involve some emissions, there is also a concept of well-to-wheel emissions, which includes not only operating emissions, but also those associated with the fuel source and other stages of the vehicle operating cycle. So, the "zero-emission" term is conditional in that sense.
The hydrogen-fueled vehicles are typically based on fuel cell technology, which imply electrochemical conversion of the fuel energy into electricity (as opposed to combustion). As a result, the only emissions of fuel cell operation are water and heat, which are not classified as harmful and therefore allow placing the fuel cell transport vehicles in the zero-emission category. The same as electric vehicles, fuel cell vehicles shift the emissions to the stage of fuel production. Thus, manufacturing of hydrogen gas via reforming of natural gas results in CO2 emissions, which must be taken into account in the life cycle assessment.
However, there is a possibility of designing a sustainable zero-emission lifecycle for electric and hydrogen vehicles, if electricity for recharging the batteries is supplied from renewable sources such as wind, solar, hydro-power converters, and the hydrogen to power fuel cells is produced via electrolysis or other emission-free technologies.
The energy conversion technologies that support the electric vehicles rely heavily on special chemistry and materials necessary to facilitate the efficient charge transfer processes. Understanding the components and principle of those technologies is important to foresee potential barriers on the way to their wide implementation and commercialization. The following learning materials will provide you with the basic knowledge on how the battery and fuel cell systems work.
A schematic representation of a generic Li-ion battery is given in Figure 10.1. Roughly, Li-ion cell consists of three layers: electrode 1 (cathode) plate (usually lithium cobalt oxide), electrode 2 (anode) plate (usually carbon), and a separator. The electrodes inside the battery are submerged in an electrolyte, which provides for Li+ ion transfer between the anode and cathode. The electrolyte is typically a lithium salt in an organic solvent.
During the charging process, a DC current is used to withdraw Li+ ions from the cathode and to partially oxidize the cathode compound:
LiCoO2 → Li1-xCoO2 + xLi+ + xe-
The released Li+ ions migrate through electrolyte towards the anode, where they become absorbed in the porous carbon structure:
xLi+ + xe- + C6 → xLiC6
At the same time, electrons travel through the external circuit (electrolyte is not electron conductive).
During the battery discharge, the reverse process takes place. Li+ ions spontaneously return to the cathode, where electrochemical reduction occurs.
Please watch this short video for an animated illustration of the Li-ion battery principle:
If we compare the energy densities of the typical rechargeable Li-ion battery (~ 0.875 MJ/kg weight) and regular gasoline fuel (~46 MJ/kg), we can see that the gasoline beat battery electricity in potential to deliver power at least by a factor of 50. Thinking that typical engine is normally used at ~50% capacity, to match the capabilities of the internal combustion engine, the Li-ion battery has to be made at least 20 times more efficient, or the size of the on-board battery should be increased 20 times, which is a prohibitive option.
Limitations of the Li-ion batteries are rooted in the material properties.
For example, the LiCoO2 ⇔ Li1-xCoO2 conversion is only reversible with x<0.5, which limits the depth of the charge-discharge cycle. But, with a wider variety of materials available, research is underway to develop new generations of Li-ion batteries.
For example, take a look at Sigma Aldrich website [19], which lists multiple alternatives for cathode, anode, electrolyte, and solvents.
Advantages | Limitations |
---|---|
Relatively high energy density and potential of finding even better formulations | Circuit protection needed to avoid damaging high voltage / current |
No need for priming - new battery is ready to operate | Aging - battery gradually loses its capacity even if not in use |
Low self-discharge (compared to other types of batteries) | Toxic chemicals are subject to regulations |
Low maintenance | High cost of materials and manufacturing process |
Capability to generate high current / power | Technology is not fully mature; varying components and chemicals |
Fuel cell is similar to a battery in the electrochemical principle of energy conversion, but different in operational design. Instead of storing the reagents and products of chemical reactions inside, like batteries do, fuel cells operate on continuous inflows/outflows of reagents and products. In that sense, they are not limited by discharge time and can generate electricity non-stop as long as fuel is supplied. Hydrogen is the best-proven fuel for fuel cells, although its storage and supply imposes some constraints on this technology.
A schematic representation of a hydrogen/oxygen fuel cell is given in Figure 10.2. The main components of the fuel cell include: membrane electrode assembly, which consists of a proton-exchange membrane and electrodes (anode and cathode) attached to the membrane on each side, gas diffusion layers, bipolar plates, and supporting structure. The fuel cell electrodes contain dispersed catalyst particles (usually platinum), which are necessary to promote electrochemical reaction.
A hydrogen-powered fuel cell combines hydrogen with oxygen in the electrochemical reaction to produce water and electricity. In case of direct contact of these gases, the reaction H2 + ½ O2 = H2O is very active and generate significant amount energy (under certain conditions – explosion). In a fuel cell, hydrogen is separated from oxygen by a proton conductive membrane, so, in order to react, it is forced to transform into ionic form by losing electrons:
H2 -> 2H+ + 2e- - this reaction occurs on the cell anode.
Further, the formed hydrogen ions (protons) are transferred through the proton-exchange membrane, while electrons are transferred through the external circuit, where they can be harvested as electric current. Once reaching the cathode, protons (H+) react with oxygen molecules, consuming electrons from circuit and producing water:
2H+ + ½O2 + 2e- -> H2O - this reaction occurs on the cell cathode.
As long as the supply of reagents, hydrogen and oxygen gases is maintained, the process continuously generates electric energy and water.
Please watch the animated illustration of this process in the following video:
The productivity of this simple process, i.e., how much electricity a single fuel cell can produce, is limited by a few factors. First is the proton conductivity of the membrane. The membrane consists of a special polymer (for example, sulfonated tetrafluoroethylene, Nafion®) which performs as an ionic conductor only under specially controlled temperature and humidity regime. This and other polymers produced for such applications are quite expensive. Second, the platinum (Pt) catalyst is necessary to provide sufficiently fast kinetics of the electrochemical reactions. Platinum is a noble metal, which has high cost and limited availability.
When it works, the fuel cell process is very efficient (80-90% efficiency) and can generate electricity pollution free and with no mechanical degradation to the cell components.
Advantages | Limitations |
---|---|
No recharging required, so the power can be generated away from electricity sources | Costly components, especially platinum catalysts |
Hydrogen-fueled fuel cells do not pollute: the only exhaust is water | High sensitivity to temperature (slow start-up when cold, degrade when hot) |
Compact cell size and possibility of stacking to fit applications of various scale | High sensitivity to impurities in fuel; catalyst is easily poisoned |
High efficiency even at low power levels | Hydrogen supply infrastructure is not developed |
No noise | On-board hydrogen storage is a challenge |
Low toxicity (compared to batteries) |
For quite a while, battery- and fuel-cell-operated cars were parallel track for future implementation of electric automotive engines, and the advancement of one or the other depended on breakthroughs in materials and device efficiency.
To overview the current status and trends in these technologies, please refer to the following reading.
Book: National Research Council. Transitions to Alternative Vehicles and Fuels. Washington, DC: The National Academies Press, 2013. Sections 2.5 and 2.6. (See E-Reserves in Canvas.)
Please read Section 2.5 to learn about the status and promise of the battery-powered vehicles.
Please read Section 2.6, "Hydrogen Fuel Cell Electric Vehicles to learn about the status and promise of the hydrogen engines for cars.
Based on the above reading, try to shape your opinion on the following question: Which type of electric vehicles in your opinion may have a better future – fuel cell or battery? Find specific arguments, pros and cons, to support it. In this lesson activity, you will be asked to perform an investigation to compare these technologies based on some common metrics. For more details, see Summary and Activity section.
Sustainable community is a term usually applied to a certain inhabited entity, a neighborhood, a town, or a city that is economically, socially, and environmentally healthy and resilient. The typical feature of a sustainably developing community is a holistic approach to meeting the local society needs, as opposed to fragmented efforts, which focus on one specific need and ignore others. Ideally, a sustainable community should have a better quality of life, which is built upon responsible and organized citizenship of its members (not on businesses compromising well-being of other communities. A sustainable community also provides economic security through reinvestments in the local economy, diverse and financially viable economic base, sustainable business (PCSD, 1997). The National Partnership for Sustainable Communities defined six principles of livability that make a community sustainable (PSC, 2014):
Availability of transportation choices is the number one factor mentioned on this list. It is interesting that transportation is one thing that becomes worse with economic growth. Other important parts of society development, like information, sanitation, manufacturing, and energy efficiency typically improve with economic development, but not transport. And now, especially, development of new mass transit options become a significant part of plans of orienting communities towards sustainable development.
Urban communities are essentially shaped by their transportation systems. Mainstream city planning in the U.S. has been based on the networks of motor roadways and personal car use, with public transit as second priority. In the second half of the 20th century, the car use and automotive fuel consumption steeply increased, as did greenhouse gas emissions from the transportation sector (~20-25% of world energy consumption). The sustainability of the current communities that are heavily reliant on car transportation becomes questionable for at least two reasons:
Development trends were slightly different in Asia and Europe, where planning was influenced by lower availability of resources or land required for automotive culture. Traditionally, European culture is more reliant on mass transit and has invested more into it. Thus, the International Association of Public Transport (UITP) based in Brussels, Belgium, supports a holistic approach to urban transportation and advocates public transportation development in 92 countries worldwide [Source: Wikipedia / International Association of Public Transport [23]]. On the average, transport emissions of a U.S. city are about 4 times higher than that in Europe and about 24 times higher than that in Asia (UITP, 2014).
Recent trends, however, show that public transit may be re-establishing its role in American metropolitan areas, as several factors suggest that transit may be a more sustainable transportation option (Rutsch, 2008). Incentives that may affect people's choice of public transit versus private cars may include economic benefits, convenience, and speed. Strategies to enhance these factors via new technologies, policies, and business models raise competitiveness of the mass transit.
Please refer to the following reading to learn about possible measures and strategies to make the public transportation more attractive in urban settings.
Penalosa, E., Role of Transport in Urban Development Policy [2], Federal Ministry for Economic Cooperation and Development, 2005.
This paper examines a range of social impacts of urban development, and especially addresses alternatives to transportation models. It also features a number of real-world examples of how transformation of mobility systems in cities contributed to the well-being of their inhabitants.
Based on this reading, try to formulate your vision of the sustainable urban community and share it on this lesson discussion forum. What are your most favorite and least favorite measures to undertake? If you had a power of policy making, what transportation model would you choose?
According to experts, modification of public transit systems through introducing new technologies would be a critical step in meeting the world's future mobility needs. The future urban transportation networks should help cities lower their per capita carbon footprint, make cities more livable by easing commute, and increase accessibility and safety. The Sustainable Cities Institute [24] names “holistic transportation” one of the key principles for urban sustainability. Holistic transportation planning with environment in mind means that besides vehicles themselves, planning should include such elements as streets, sidewalks, pedestrian spaces, bicycle routes, and enabling technologies for private and public fleets.
The following video features a few innovations related to long-distance and short-distance transit, which are discussed in the context of sustainable city planning. Although some technologies and ideas sound and look somewhat futuristic, others started their way up the TRL scale and get much closer to commercialization.
A couple of points / questions to focus on while watching the video:
As 95% of transportation energy currently comes from petroleum, significant restructuring of the transportation sector would be required to reach sustainable operation in the future society. This is one of the areas where breakthrough in technologies are in the highest need, and success in research and implementation of those technologies in the nearest ten to fifteen years would dictate what vehicles the next generations will be driving. Strong reliance of vehicles on infrastructure of fuel supply makes the problem of transition to new transportation technologies even more complex. The activity in the end of this lesson touches upon some key technologies employed in zero-emission vehicles, which may or may not become a significant part of the future transportation system. You get a chance to explore this question on your own and make your prediction.
Type | Assignment Directions | Submit To |
---|---|---|
Reading | Complete all necessary reading assigned in this lesson. | |
Discussion |
Based on reading Penalosa, E., Role of Transport in Urban Development Policy [2], Federal Ministry for Economic Cooperation and Development, 2005 (see page 10.3). Formulate your vision of the sustainable urban community and share it on this lesson discussion forum. What are your most favorite and least favorite measures to undertake in order to modify the current transportation system? If you had a power of policymaking, what transportation model would you choose? Comment on at least one other post on the forum. Response to any questions asked to your posts. Deadline for initial posting: this Sunday, for comments: Wednesday. |
Canvas: Lesson 10 Discussion |
Activity |
After reading sections 2.5 and 2.6 of the book, "Transitions to Alternative Vehicles and Fuels". Washington, DC: The National Academies Press, 2013. (see page 10.2 of this lesson), perform independent investigation and compare three transportation options listed below:
Imagine that you need to take a road trip from New York to Chicago (~800 miles), and based on that scenario, evaluate the above transportation options by the following metrics:
For this hypothetical case, you can assume that no maintenance is required to the cars during the trip (except for re-fueling/ re-charging). You can use approximated data as needed, but explain your assumptions. Present your numerical results in the table. Show your calculations. Provide a discussion to address the following question: Which type of electric vehicle in your opinion may have a better future – fuel cell or battery? Support your argument with some listed pros and cons and numbers. You can also say “both” or “neither” but provide proper argument. Make sure to provide proper citations for data sources. Please see more details in the Lesson 10 Activity Sheet posted on Canvas Deadline: Wednesday (before midnight). |
Canvas: Lesson 10 Activity |
Battery University, Is Lithium-ion the Ideal Battery?, 2010, URL [28], accessed 2014.
PCSD, President's Council on Sustainable Development, Sustainable Communities, Task Force Report, 1997.
Popovich, N. and Lu, D., The Most Detailed Map of Auto Emissions in America, The New York Times, Oct. 10, 2019. URL [12], accessed 4/3/2020
Rutsch, R, The Role of Public Transit in Sustainable Communities [27], Sustainable Community Development Code Research Monologue Series, The Rocky Mountain Land Use Institute, 2008.
Sierra Club, U.S. Oil Dependence Threatens Security, Economy, Environment [29], accessed July 2014.
UITP, Advancing Public Transport [30]; accessed 2014.
U.S. DOE, Transportation Fuels: The Future is Today, NEED 2007.
Links
[1] https://www.bcuc.com/Documents/Proceedings/2019/DOC_54746_A2-19-Stillwater_Fuels_Supply_Chain.pdf
[2] http://www.sutp.org/files/contents/documents/resources/A_Sourcebook/SB1_Institutional-and-Policy-Orientation/GIZ_SUTP_SB1a_The-Role-of%20Transport-in-Urban-Development-Policy_EN.pdf
[3] https://www.pexels.com/photo/white-and-orange-gasoline-nozzle-110844/
[4] https://www.pexels.com/search/mike%20b/
[5] https://www.pexels.com/
[6] http://biofuel.org.uk/
[7] http://energyeducation.ca/encyclopedia/Natural_gas_vehicle
[8] http://www.world-nuclear.org/information-library/non-power-nuclear-applications/transport/transport-and-the-hydrogen-economy.aspx
[9] https://www.eei.org/issuesandpolicy/electrictransportation/Pages/default.aspx
[10] https://www.e-education.psu.edu/eme807/sites/www.e-education.psu.edu.eme807/files/files/lesson_10/DOE_Alternative-Fuels_p27.pdf
[11] https://www.usatoday.com/story/news/politics/2020/03/31/trump-eases-up-obama-era-fuel-efficiencies-rules-cars-trucks/5093923002/
[12] https://www.nytimes.com/interactive/2019/10/10/climate/driving-emissions-map.html?mc=aud_dev&ad-keywords=auddevgate&subid1=TAFI&ad_name=INTER_20_XXXX_XXX_1P_CD_XX_XX_SITEVISITXREM_X_XXXX_COUSA_P_X_X_EN_FBIG_OA_XXXX_00_EN_JP_NFLINKS&adset_name=https%3A%2F%2Fwww.nytimes.com%2Finteractive%2F2019%2F10%2F10%2Fclimate%2Fdriving-emissions-map.html&campaign_id=23843902735120063&fbclid=IwAR3OZgTwah3RQAbfve3igBJp0oVoNizn6A4h1PO0OR-JMpS15noupACylHI
[13] https://www.nytimes.com/2019/03/26/nyregion/what-is-congestion-pricing.html
[14] https://www.flickr.com/photos/hayano
[15] https://www.flickr.com/photos/usnavyresearch
[16] https://commons.wikimedia.org/wiki/File:Li-Ion-Zelle_(CoO2-Carbon,_Schema).svg
[17] https://www.youtube.com/c/basf
[18] https://www.youtube.com/embed/9fV-PqD0mbI
[19] https://web.archive.org/web/20120625050358/http://www.sigmaaldrich.com/materials-science/material-science-products.html?TablePage=106039040
[20] https://www.youtube.com/c/HondaVideo
[21] https://www.youtube.com/embed/8rofx6Gaz40
[22] https://www.flickr.com/search/?text=Keromi%20Keroyama
[23] http://en.wikipedia.org/wiki/UITP
[24] https://www.nlc.org/program-initiative/sustainability
[25] https://www.youtube.com/c/CNBCInternationalTV
[26] https://www.youtube.com/embed/NtQKQEIsoMk
[27] http://www.law.du.edu/images/uploads/rmlui/rmlui-sustainable-publicTransit.pdf
[28] https://batteryuniversity.com/index.php/learn/archive/is_lithium_ion_the_ideal_battery
[29] https://www.americansecurityproject.org/u-s-oil-dependence-threatens-security-economy-environment-new-joint-report-shows-the-problems-with-and-solutions-to-u-s-oil-addiction/
[30] http://www.uitp.org