Abstract
Public or private transportation is a big issue in trying to cut and maintain low CO2 emissions. This issue has become controversial in some circles so this paper uses math to determine which choice is better for me. Data from the Australian Greenhouse Office, the Australian Bureau of Statistics and the United States Energy Department is used. These government offices have reported transport emissions as compared to the emissions of other public sectors. Also different modes of transportation and their fuel types are reported upon as compared to passenger activity and energy use. According to the calculations the use of cars or motorcycles regardless of the type of fuel is not good for the environment. Other modes of public travel use energy more efficiently based on per passenger activity. The results demonstrate that city coordination to continue to make public transportation more efficient will help cut CO2 emissions. The conclusion is the public city buses system is the most efficient use of energy per passenger; therefore it adds the least to CO2 emissions. Using public transport makes good sense.
(public transport, private transport, CO2 emissions, greenhouse gases, transport modes, passenger activity)
Public or Private Transportation
There are so many variables to consider economic and environmental that making a decision about whether to use public or private transportation can be confusing. Walking is the best choice for the environment and the easiest because of the availability of sidewalks and safe crosswalks. Bicycling is the next best choice because no CO2 is emitted. When bike trails are available or bike racks on buses and trains are available then bicycling is a good choice.
Using information collected from the Australian and the USA government I have used math to look at some of the data to help me decide which is better. The Australian Greenhouse Office (2002) has reported greenhouse emissions in tonnes per year and percent per year listed by application shown in Table 1. Transport produces the highest percentage of greenhouse emissions.
Source: Australian Greenhouse Office CSIRO: National Kilowatt Count of Household
Energy Use, 2002)
Here is how the 49.6% of greenhouse emissions in the transport sector was calculated. The amount of tonnes per year greenhouse admissions per application is the sum of the first column. 13.6 + 3.3 + 4.2 + 0.3 + 2.1 + 1.1 + 0.8 + 0.5 + 0.5 + 1.0 = 27.4 tons/yr Total
Since 13.6 tonnes per year are due to transport we need to divide 13.6 by the total and obtain the percent per transport mode.
13.6/ 27.4 * 100 = 49.6350 which can be rounded off to 49.6%.
The average of the tonnes per year for the ten applications is 27.4 tons/yr divided by10 which equals 2.7. The median is 1.0 + 1.1 = 2.1/2 = 1.05. Both the average and the median are misleading in this example because the range of tonnes per year from 13.6 to 0.5 is heavily weighted to the emissions of transport because the account for almost 50% of the total tonnes per year greenhouse emissions.
Figure 1 and Figure 2 are better at giving a true picture visually of how transport is responsible for the largest amount of greenhouse emissions in the applications compared.
Figure 1 Tonnes per year = the y-axis and Mode of emissions = x-axis
(Source: Australian Greenhouse Office / CSIRO: National Kilowatt Count of Household Energy Use, 2002)
These bar graphs have the same size and shape although one is the graph of tonnes/yr and one is the graph of emissions per year in per cent.
Figure 2 Percentage for 0 to 60 = y-axis and the Mode of emissions = x-axis
(Source: Australian Greenhouse Office / CSIRO: National Kilowatt Count of Household Energy Use, 2002)
For those modes of transportation needing fuel the Australian Greenhouse Office has made Table 2 to present the amounts of energy use and emissions use per passenger kilometer traveled. Cars, the most popular mode of private transportation, are rated the highest in both regardless of fuel (regular petrol gas, light petrol gas or ethanol). Interestingly buses show no change in energy use regardless of type of fuel.
Table 2 Energy use (MJoules per passenger kilometers)
and CO2 emissions (g per passenger-km).
(Source: Australian Greenhouse Office /
CSIRO: National Kilowatt Count of Household
Energy Use, 2002)
The average emission for the car passengers is (286+256+253)/3= 265 g/km; for the tram there is one type, electric which measures 253 g/km; for the buses (19+18+16)/3=17.7 g/km; for the two types of trains (16+14)/2= 15 g/km; and the average of the two engine sized motorcycles is (124+178)/2= 151 g/km.
Average emissions per transport type.
Cars - 265 g CO2/passenger km
Tram - 253 g CO2/passenger km
Buses - 17.7 g CO2/passenger km
Trains - 15 g CO2/passenger km
Motorcycles - 151 g CO2/passenger km
Buses and trains are best for the environment according to this data. If a student has to ride 10.5 kilometers to school every day she will cause 2597 g less CO2 emissions to the air by taking the buses than by having her parents drop her off at school.
265 g CO2/passenger km * 10.5 passenger km = 2783 g CO2
17.7 g CO2/passenger km * 10.5 passenger km = 186 g CO2
2783 g CO2 - 186 g CO2 = 2597 g CO2
The bar graph in Figure 3 shows the large difference in emissions caused by cars and motorcycles compared to the other transport modes.
Figure 3 Energy use per transport fuel type and vehicle stated it as Energy Use in MJ/ passenger-km.
Source: Emissions intensity figures from Australian Greenhouse Office, AGO Factors and
Methods Workbook 2006.
Figure 4 has the litres/100 km used by passenger cars in respect to time (1960 to almost 2010). The shape of the curve demonstrates that the trend for fuel efficiency has been improving overall during the decades. In Australia increasing until mid 70s avg increase in efficiency went from 12.4 to 11.6 in about 30 years. This demonstrates that this was not a governmental priority to increase fuel efficiency.
Figure 4 Average Fuel Efficiency of Passenger Vehicles for 5 Decades.
Litres/100km on the y- axis and Years on the x-axis.(Source: Australian
Bureau of Statistics (ABS) has conducted a Survey of Motor Vehicle Usage)
Figure 5 depicts the range of total energy use per transport mode. For example, the car at the low side of the range consumes approximately 3 MJ/passengers-km. At the highest end of the range the car consumes approximately 4.8 MJ/passengers-km. total energy use per Million Joules/passenger kilometer. The total range of low to high in energy use is higher in the cars than in any of the other transport modes; demonstrating that cars are not an efficient way to use energy. The energy consumed for manufacturing and operation are included in the energy use totals.
Figure 5 Life-Cycle Efficiency of Passenger Vehicle per Total energy use Range of energy use
Bureau of Statistics (ABS) has conducted a Survey of Motor Vehicle Usage)
Figure 6 presents a comparison of Highway Passenger Activity between busses versus cars and trucks overtime. The statistics in Table 3 lists the differences in activity between
Figure 6 Highway Passenger Activity graphed as Million Passenger Miles over time.
(Source: USA Dept of Energy. Transportation Sector. Energy Intensity Indicators. Accessed from <www.eere.energy.gov/intensityindicators>.)
the two modes of transportation. The activity has been increasing linearly since the 1970s and the correlation coefficient is 0.9 for the busses and 0.98 for the cars and trucks indicating strong linearity.
In Table 3 for the above Figure 6 columns the highway passenger activity for cars and trucks averaged for the past ten years 4,059,596 P-M; while for the busses it averaged 143,137 P-M. The past ten years growth for the cars and trucks was 25.1% and for the buses was 0.6%. The table also presents the past twenty year growth and the past thirty years growth for the two modes of transportation. Overall there was a 91.7& increase in passenger cars and trucks and a 65.8% increase in busses.
Figure 7 depicts the trend in personal passenger activity in cars and light trucks. The activity has been increasing linearly since the 1970s and the correlation coefficient is 0.9 for the cars and 0.98 for the light trucks indicating strong linearity.
In Table 3 for Figure 7 the personal passenger activity average for cars averaged for the past ten years 2,542976 P-M; while for the light trucks it averaged 1,516,622 P-M. The past ten years growth for the cars was 18.4% and for the light trucks was 37.2%. The table also presents the past twenty year growth and the past thirty years growth for the two modes of transportation. Overall there was a 38.9% increase in passenger cars and a 326.7% increase in light trucks.
Figure 8 depicts the Buses Passenger Activity including three different types of busses: the urban buses, the intercity buses and the school buses. Table 3 reports the mean for the ten-year-periods as follows: for the urban buses – 20, 623 P-M, for the Inter City buses – 35, 213 P-M and for the School busses – 87,300 P-M. For the past ten years activity for the urban buses rose 13%, for the Inter City buses rose 38.5% but for the School buses declined -13.1%. The 30 year growth for Urban buses is 16.2%, for Inter City buses is 55.1% and for School buses is 96.1%. This demonstrates that the school buses activity growth rose more in the two prior decades than in the contemporary decade. Figure 8 Buses Passenger Activity graphed as Passenger Miles over time and depicting the average with the standard deviations.
(Source: USA Dept of Energy. Transportation Sector. Energy Intensity Indicators. Accessed from <www.eere.energy.gov/intensityindicators>.)
According to the calculations the use of cars or motorcycles regardless of the type of fuel is not good for the environment. Other modes of public travel use energy more efficiently based on per passenger activity. The results demonstrate that city coordination to continue to make public buses transportation more efficient will help cut CO2 emissions. I would suggest coupling more passenger- friendly services such as bicycle racks on the front of buses and staying on a consistent schedule to help encourage buses use. I will choose public transport over the other transportation methods which also use fuel.
Source: Australian Greenhouse Office. National Greenhouse Gas Inventory: Analysis of Recent Trends and Greenhouse Indicators 1990 to 2002, and Australian Methodology for the Estimation of Greenhouse Gas Emissions and Sinks 2002: Energy (Transport). Industry figures for public transport power consumption and PTUA calculations.
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