Thursday, June 25, 2009

Plugging the Tail Pipe – Reducing Emissions from Transportation

In a previous post an analysis was conducted to investigate what steps would be required to meet the current emission cap provided by the ACES. In the analysis three scenarios were outlined with regards to emission reduction from the transportation sector. These scenarios were merely markers regarding how to view certain reduction percentages. The recent establishment of new mileage standards for cars and trucks is expected to be a critical driving (ha, ha) factor in the reduction of transportation originating emissions. However, how many tons of emissions will be saved under these new milage standards and what scenario of reduction will these new standards attain? The following analysis aims to answer those questions.

In 2007 the transportation sector accounted for 2,014,365,849 tons of carbon dioxide (CO2) emissions.1 These emissions arise largely from the combustion of gasoline. The amount of emissions that are released due to the combustion of gasoline are calculated as followed:

40 Code of Federal Regulations (CFR) 600.113-78 assigns a carbon content of 2,421 grams to every gallon of gasoline, which translates to 8,877 grams (19.6 lb) of CO2.2 This value is where most calculations stop, however, typically only 99% of the carbon is oxidized therefore, only 8,788 grams (19.4 lb) of CO2 are actually released.3 For the purpose of this analysis 19.4 lb or 0.0097 tons of CO2 are released for gallon of gas burned during travel. Divide this value by the average mpg of the vehicle to calculate the average CO2 generated per mile driven.

CO2 is not the only GHG that is emitted when burning gasoline. CH4, N2O and HFC are also released. However, calculating the exact amounts for these other gases is difficult. The EPA uses a simplified method of calculation where the CO2 estimate is multiplied by 100/95 to account for the 5% compilation of non CO2 GHG emissions.3

Most of the critical details regarding President Obama’s plan to increase fuel economy standards have yet to be determined or announced. Currently the major talking point is an average fuel economy for passenger cars of 39 miles per gallon and an average fuel economy for trucks of 30 miles per gallon.4 However, few details have been released regarding whether or not electrical and hybrid models will be factored into this average or whether or not light duty vehicles are included in the truck section along with other critical issues.

In 2006 the US Bureau of Transit Statistics reported that there are 250,851,833 registered vehicles in the United States. 135,399,945 (53.98%) of these vehicles are automobiles and another 99,124,775 (39.515%) are classified ‘other 2 axle, 4 tire vehicles’.5 For the purposes of this analysis 70% of these ‘other 2 axle, 4 tire vehicles’ will be classified as light trucks and the others will be classified as others types that do not fall under the new fuel economy standards put forth by President Obama (light duty vehicles etc.). The remaining 6.505% of registered vehicles will not be regarded as passenger fleet vehicles. Note that passenger fleet in this particular sense refer to vehicles that are affected by President Obama’s new fuel efficiency standards.

Estimating an average miles driven per year is a little tricky because all of the rating sources include all fleet vehicles even those that are over 10 years old as long as they are still officially registered. However, in most situations it is unlikely that most of these vehicles actually drive the average of younger vehicles. MOBILE6 calculated an annual average mileage of approximately 12,000 for passenger cars and 15,000 miles per year for light trucks.3

The analysis was carried out under two time periods one from 2006 to 2016 when the mileage standards are supposed to be officially met and one continuing to 2020.

The assumptions used in the analysis are as followed:

The age of a vehicle will be tracked and assigined their respective fuel economy based on the year it was purchased. Vehicles will be replaced after a lifecycle of 12 years.

This assumption basically removes a level of equality from the car fleet. Each group of cars have their own fuel economy, but a constant rate of replacement. Assuming a wide variety of car ages on the road represents reality much more accurately than assuming all of the cars are from a particular year.

A balloon increase is applied for fuel economy increases between 2009 and 2016.

Although the Obama administration has assigned target goals for the year 2016, no checkpoint goals were assigned for the years leading up to 2016. Some report indictate that there will be markers from 2012 to 2016, but these markers have apparently not be identified. Therefore, it was assumed that for both cars and light trucks initial gains in fuel economy would be slower than gains made later due to the possibility of new technology emerging and pressures to met the 2016 deadline.

An average growth of cars and light trucks on the road of a net +1% from 2006 to 2011 and a net +2.5% from 2012 to 2016 (2020).

Due to influences of the economic recession and credit crunch it makes sense to assume a low growth rate on the purchase of new automobiles over a short-time period. However, with new mileage standards developed in the mid part of the next decade it seems reasonable that individuals will be looking to invest in a new car to save money on rising gas prices suggesting a higher rate of growth.

Fuel Economy Standards do not include the use of hybrids or electric cars in their computation.

This assumption is similar to a mathematician making the assumption that x object is like a sphere. It makes the calculations a lot simplier, by removing the headache of calculating what gas mileage hybrids will receive based on pattern driving and average drive time. The goal of this analysis is to investigate more optimistic than pessemistic outcomes and gauge whether or not those optimistic results will accomplish what is needed. Not including hybrids or other electrical vehicles in the fuel economy standard implies a dramatic increase in fuel economy efficiency and the ideal situation for emission reduction.

To avoid significant complications regarding car age vs. emissions, when vehicles enter the passenger fleet they will be new, i.e. no used vehicles are ever purchased.

Fairly self-explanatory, albeit somewhat unrealistic.

Each year when new cars are purchased, the average fuel economy anticipated for the given year is translated to the average fuel economy between the new vehicles purchased.

Basically if the average fuel economy for all vehicles that can be purchased in 2015 is 30 miles per gallon, consumer purchase of new vehicles in 2015 will have an average fuel economy of 30 miles per gallon.

Biofuel blends were not included in the analysis of emission reduction due to fuel replacement questions.

Overall biofuel production from non-food derived sources is not nearly significant enough to warrant its inclusion in this analysis. In addition currently there is not a clear plan for the rapid incorporation of biofuel into the automobile infrastructure (widespread biofuel gas pumps, biofuel based car dealerships etc.) to properly generate a map of inclusion. Perhaps an updated analysis will include biofuel blends.

The analysis first assigned ages to the current registered pool of cars and trucks using information from the 2001 study on car age by the National Automobile Dealers Association and assuming an equal percentage between age ranges. Due to the average vehicle age being a little over 8 years the ratio was generally assumed constant over the last half decade. The percentage breakdown was as followed: (10-12 years = 38.3%; 7-9 years = 22.3%; 3-6 years = 25.8%; 0-2 years = 13.6%)

The results of the assignment are shown in the table below.

* = purchased within the last year;

Mileage data for other passenger cars and light trucks for use in this analysis were taken from EPA information.6 Due to the maximum vehicle age of 12 years and the initial starting year of 2006, fuel economy history starts at 1994 and proceeds linearily corresponding to vehicle age. The average fuel economy used for various past years is shown in the table below.


Two different scenarios were investigated for the progression of fuel economy standards, one under President Obama’s plan and one excluding a direct goal (this growth will be referred to as standard growth). The growth of fuel economy under standard growth consisted of a constant 0.2 miles per gallon increase per year for cars and 0.15 miles per gallon increase per year for light trucks. This increase was necessary because realistically with the advent of the electric car as well as the continuing threat of higher gas prices it would be na├»ve to assume that mileage standards on vehicles would stagnate even without a directive from the White House or Congress and that consumers would not elect to purchase more fuel-efficient vehicles. It would behoove automobile companies to increase fuel economy as a means to increase sales; however, increases would be slow to keep down costs. The table below outlines the estimated fuel economy growth for both President Obama’s plan and under the standard growth model for cars and light trucks. Any growth beyond 2016 was assumed to follow the standard growth model.

* % difference is related to the size difference between the two plans relative to the standard growth model;
Emissions were calculated by totaling all of the emissions produced by vehicles at their various ages. Individual emissions per year from age groups were calculated via the following formula:

Dave/MPGm * Vehiclen * CO2 * (100/95) (1)
where Dave = average miles driven per year; MPGm = fuel economy for the given vehicle in year m; Vehiclen = number of vehicles of n years of age; CO2 = CO2 emissions per gallon of gas consumed;
Based on the outcome of this analysis the total tons of CO2e saved for passenger cars from 2006-2016 is 323,546,844 and light trucks is 292,406,997 for a total reduction of 615,953,841 tons of CO2e. The table below documents all of the yearly reductions.

Note that there is no reduction in emissions between 2006 and 2008 because the analysis utilizes passenger vehicle registry information from 2006, so the analysis need to begin in 2006, but the fuel economy information is relevant up to 2008. Therefore, there is no difference in fuel economy between President Obama’s plan and the standard growth model between that time period as shown in a previous table.

Two issues can be immediately drawn from the results of the analysis. First, the results for the 2006-2016 time period are not encouraging with regards to the emission reductions demanded by the three transportation emission reduction scenarios outlined in the previous post discussing the energy gap. The table below outlines the difference in emissions that the White House program will develop vs. the emission reduction required for each of the three scenarios.

* the % difference is with respect to the emissions demanded by the given scenario;

These new emissions standards, although abmitious, do not even reach the poor level of expectations. Recalling the results from the energy gap analysis, only one of the possible nine investigations was successful using the poor result for emission reduction and that investigation required the optimistic outcome from all other scenarios, clearly not an outcome that is probable and still that result failed the secondary tests for success. The problem is that most of the reductions from the new emission standard is spent neutralizing what will occur, thus there is little left to work against what needs to be reduced from 2007.

Second, early sound bites report that the administration claims that 900 million tons of CO2e will be saved by this program.7 This claim falls far short of the reduction seen in this analysis (only 68.44% of that estimation). This difference highlights a critical issue with statements taken from the media, rarely do they cite any assumptions that go into the claim. The above analysis tries to be as fair and realistic as possible, yet the result is considerably smaller than anything President Obama’s administration predicts. It is difficult to respect the validity of the White House prognostication because there are no assumptions presented to how it was derived. This information gap is exactly why public statements need to be backed up by cited analysis and/or assumptions so the validity of the statement can be directly addressed.
When looking at extending the emission analysis to 2020, the relevant year pertaining to the energy gap, the total tons of CO2e saved for passenger cars from 2006-2020 is 893,036,956 and light trucks is 803,450,943 for a total reduction of 1,696,487,899 tons of CO2e. The change is much more significant than one might originally anticipate. Overall the additional four years leads to an additional saving of 1,080,534,058 tons of CO2e. The table below documents all of the yearly reductions for the 2006-2020 analysis.

The primary reason for such a dramatic increase in emission reduction is the separation of fuel economy between President Obama’s plan and the standard growth model. Early in the analysis most of the active cars are those that have fuel economies prior to the new targets set by President Obama. However, as those cars age and are replaced with newer models the fuel economy difference between the two models expands. The additional four years between ending at 2016 and 2020 creates further separation whereby 2020 only the 12-year old cars (2008 purchase) still equate a fuel economy between the two models. When expanding the program to 2020, how well do these new targets do at meeting the proposed emission scenarios?

Expansion to 2020 does a better job of trying to attain the poor scenario, but still fails.

Although the President Obama’s fuel economy goal does significantly reduce emissions, the result is still lacking according to the energy gap analysis. However, this first part of the analysis leaves out an important element in the reduction of transportation emissions, electric vehicles. Although the previous energy gap analysis assumed that electric vehicles would not be responsible for any reductions in the transportation sector due to a lack of infrastructure, what would be the result if they were included in some respect?

For the purpose of this analysis a simplistic model of the electric car was utilized where charge only flows one way from the outlet to the car, the car was not able to return surplus to the grid. A value of 0.225 kW-h per mile was utilized to describe the emission potential of the electric car used in this analysis. The same yearly mileage expectations were utilized for electric cars.
The establishment of the grid is a little tricky. Due to the ideal of reducing energy generating emissions over time the grid providing electricity to the car will be in a state of flux. Based on the previous analysis of the energy gap, it is highly probable that the shift in energy generation will move from coal to natural gas with a small addition made by zero emission renewables (in this analysis a 2.5% increase in total energy generated is supplied by renewables). The flux of the grid is shown in the table below with 2006-2016 in the second and third column and 2006-2020 in the fourth and fifth.

With this information each portion of the emissions can be calculated for any electric car fleet via the following equation:

Vehicle # * [Dave * Euse / Emissionratio * %Power Type]n (2)

where Euse = Energy used per mile; Vehicle # = Number of Electrical Vehicles; Emissionratio = MW-h per ton of CO2; % Power Type = Mode of Energy Generation [Coal, Natural Gas or Renewable];

The final issue with regards to electric vehicles was their incorporation into the fleet. Overall it would unrealistic to expect any serious change in electric car ownship until at least late 2010 when serious models are introduced like the Volt (sorry Tesla). Add another year to create a reasonable infrastructure and expand plug-in assessories. Therefore, 2012 was assumed to be the start year for significant incorporation of electrical vehicles into the fleet. Electric car purchasing was thought to increase by 3% per year from the start year of 2012 until acquiring the requisite 10 or 20% at the end year of the analysis (2016 or 2020).
Based on the emission saving potential of an electric vehicle the previous standard of car replacement only after 12 years was dismissed and instead a new replacement procedure was designed for electric cars. It was hypothesized that the older the car the more likely the owner was to replace it with an electric car. The table below outlines the replacement probability.

The total tons of CO2e saved for passenger cars from 2006-2016 is 530,675,840 and 737,789,372 tons of CO2e when replacing 10% and 20% of the fleet with electric cars respectively.

The total tons of CO2e saved for passenger cars from 2006-2020 is 1,237,952,164 and 1,593,326,221 for 10% and 20% electric car incorporation respectively. Note that more of that reduction actually comes from the increase in fuel economy extension from 2016-2020 than conversion to electric cars.
The table below documents all of the yearly reductions from electric car incorporation for 2006-2016.

* Compared against the Obama plan, a positive number indicates a percent greater reduction from electric, a negative number indicates a percent greater reduction in Obama plan;

From the data there is no change between 2006-2011 because electric cars are not incorporated into the fleet until 2012. However, it must be noted that the emission reduction values estimated in this analysis for electric cars are probably inflated by 1-3% because when computing the emissions from electrical sources only CO2 was considered and not other GHGs, whereas all GHGs produced from the combustion of gasoline were considered. Also electric car incorporation requires an additional 43,473,510 MW-h and 86,947,021 MW-h of energy for 10% and 20% respectively.
The results on electrical car incorporation and how it compares to the three transportation emission reduction scenarios are shown in the tables below, the first being for 2006-2016 and the second 2006-2020. Note that no trucks were estimated to be electrical in the analysis, thus the truck emission reduction data is the same as the first part of the analysis.

Inclusion of electric cars generates a significant improvement in the ability to meet the poor transportation reduction scenario (for 2020). However, estimating a 20% conversion within the entire passenger car portion of the vehicle fleet in only approximately 5-10 years seems rather optimistic to the point where it is unrealistic. The problem is when electric cars are introduced in late 2010, it is probable that they will be more expensive than a combustion engine vehicle which may reduce probability of purchase. Also it may take longer to set up an appropriate electrical car infrastructure, where the electric car is the one that a commuter takes for that 10-20 mile drive to and from work instead of the combustion engine, than the year estimated here. Finally if anything ever goes wrong with an electric car that cannot be explained away as an isolated incident, say good-bye to any significant growth in purchase for 1-2 years.

Another element missing is specifics about the fuel economy targets, most notably how will the target points of 39 mpg and 30 mpg be calculated? Will automobile manufactures be allowed to average all available for purchase vehicles to determine their average fuel economy (combustion, hybrids, plug-ins and 100% electrical)? That scenario seems to be the most probable which then will further reduce the total emissions reduced from the program vs. the assumption made for this analysis in that all combustion vehciles averaged the target point. In this analysis the fleet average for passenger cars for a given manufacture that included electrical, hybrids and others was actually higher than 39 mpg. Also there is the aforementioned problem of consumer behavior. Just because a fleet averages 39 mpg it does not mean that consumers will purchase vehicles which those fuel economy standards despite the assumption to the contrary in this analysis.

For example suppose that manufacture A includes enough hybrids etc. so that their non electrical models only have to average 34.5 mpg. Using 34.5 mpg instead of 39 mpg on a 10% electrical cars purchase model reduces the emission reduction for cars from 2006-2016 from 530,675,840 tons of CO2e to 435,684,982 tons of CO2e or 17.9%. Clearly it is important to assign clear and binding guidelines to how the fleet average fuel economy for a given car manufacture will be calculated.

Finally when talking about emission reductions in the transportation sector, the media likes to flash around the equavlent number of cars that a certain policy or piece of legislation would remove from the road. In this analysis a press statement could be made that through the course of the program, President Obama’s target would take the equvalent of 121 million cars off the road. That sounds like a big number (lower than the 177 million that the White House throws around), but when crunching the real numbers and applying meaning to the ‘cars off the road’ number, it loses a lot of its power. The ‘removed’ stat can be very misleading in that in actuality it only refers to one year not permanently. So when someone states that such-and-such an action is like removing 100 million cars from the road, it actually means that such-and-such an action is like removing 100 million cars from the road for one year. Therefore, it is important not to get caught up in the sound bites and look for the real information. Overall based on this analysis President Obama’s fuel economy target will reduce CO2 emissions from the transportation sector and is a good start, but much more needs to be done if the appropriate transportation reductions are going to be met by 2020.
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1. “Emissions of Greenhouse Gases Report” Table 5. U.S. Carbon Dioxide Emissions from Energy and Industry, 1990, 1995, 2000-2007. Energy Information Administration. Dec 2008.

2. 40 Code of Federal Regulations (CFR) 600.113-78 - Fuel economy calculations. http://cfr.vlex.com/vid/600-113-78-fuel-economy-calculations-19827802

3. Emission Facts: Greenhouse Gas Emissions from a Typical Passenger Vehicle. Environmental Protection Agency. EPA420-F-05-004 February 2005.

4. Allen, Mike and Javers, Eamon. “Obama announces new fuel standards.” May 19, 2009. http://www.politico.com/news/stories/0509/22650.html

5. Table 1-11: Number of U.S. Aircraft, Vehicles, Vessels, and Other Conveyances. US Bureau of Transit Statistics. http://www.bts.gov/publications/national_transportation_statistics/html/table_01_11.html

6. “Light-Duty Automotive Technology and Fuel Economy Trends: 1975 Through 2008.” Appendix C - Fuel Economy Distribution Data. Table C-5: Sales Weighted Percentile Distribution of Adjusted Composite Car Fuel Economy and Table C-6: Sales Weighted Percentile Distribution of Adjusted Composite Truck Fuel Economy. Environmental Protection Agency. September 2008.
7. “President Obama Announces National Fuel Efficiency Policy.” The White House - Office of the Press Secretary. May 19, 2009. http://www.whitehouse.gov/the_press_office/President-Obama-Announces-National-Fuel-Efficiency-Policy/












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