Kiera Jefferson
The transportation sector is a significant contributor to greenhouse gas emissions, with GHG emissions from transportation accounting for about 28% of total US greenhouse gas emissions. Buses, as a form of public transportation, play a role in reducing these emissions by offering an alternative to private car usage. The impact of buses on pollution levels is a topic of ongoing debate, with some arguing that bus transit reduces greenhouse gas emissions, while others claim that it is not a greener choice than driving a car. Various factors, such as occupancy levels and fuel type, influence the environmental impact of bus transportation.
What You'll Learn
Public transport saves fuel
Firstly, public transport is more energy-efficient than private transport. Trains, for example, are around 20 times more energy-efficient than cars. This is because their efficiency increases with the number of passengers they carry. A tube train during rush hour, carrying 1000 people, uses very little energy per passenger. Similarly, buses are well-suited for alternative fuels, with nearly 60% running on lower-emission, cost-saving options. They can also carry more passengers, achieving a higher passenger-mile per gallon.
Public transport also saves fuel by reducing congestion. The latest research shows that in 2011, US public transportation saved 865 million hours in travel time. Without it, congestion costs in 2011 would have risen by nearly $21 billion from $121 billion to $142 billion in 498 urban areas. This reduction in congestion leads to a reduction in the fuel used by private vehicles.
The impact of public transport is also seen in the savings it creates. Public transportation in the US saves the equivalent of 4.2 billion gallons of gasoline annually and more than 11 million gallons of gasoline per day. This is the equivalent of 300,000 fewer automobile fill-ups every day.
Additionally, public transport saves fuel by reducing the number of cars on the road. A single person switching from a 20-mile solo commute by car to public transportation can reduce their annual CO2 emissions by 20 pounds per day, or 48,000 pounds in a year. This is equal to a 10% reduction in greenhouse gases produced by a typical two-adult, two-car household.
To encourage the use of public transport, agencies are improving convenience by helping passengers link multiple transportation modes. For example, by making bicycle or scooter storage available on buses, travellers can easily move between transportation modes.
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CO2 emissions per passenger
The CO2 emissions per passenger for a bus journey depend on several factors, including the number of passengers on the bus, the distance travelled, and the type of fuel used.
According to one source, a bus emits 299 grams of CO2 per passenger mile, which is the second-worst only to cars, which emit 371 grams per mile. Another source gives a lower estimate of 22-92 gCO2-eq/pkm (grams of CO2 equivalent per passenger kilometre) for buses. This source also states that the emissions per passenger decrease as the number of passengers increases. For example, a full bus (with 50 to 80 passengers) can carry as many people as 50 to 60 cars, which typically have fewer than 2 occupants. This means that, in addition to being more fuel-efficient than cars, buses can significantly reduce emissions by transporting more people.
When compared to other modes of transport, buses generally emit less CO2 per passenger than short-haul flights, especially for shorter distances. For example, a 200-mile trip on a plane would emit around 109 pounds of CO2 per passenger, while the same trip on a bus would emit 19 pounds of CO2 per passenger. Similarly, a domestic flight emits 246 grams of CO2 per kilometre, while a bus emits significantly less. Trains are also a more environmentally friendly option than buses, with electric trains emitting around 4 grams of CO2 per passenger kilometre, and trains in general emitting 177 grams of CO2 per passenger mile.
In terms of overall environmental impact, public transportation, including buses, has been shown to have significant benefits. For example, the use of public transportation in the US saves the equivalent of 4.2 billion gallons of gasoline annually and reduces greenhouse gas emissions. Additionally, public transportation helps to reduce congestion and can lower an individual's carbon footprint by up to 6,000 pounds of CO2 annually.
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Fuel economy and costs
The fuel economy of a bus is influenced by several factors, including road parameters, driver behaviour, weather conditions, and vehicle parameters. For example, a diesel school bus that achieves 8.5 miles per gallon will cost approximately $4,328.70 to fuel for a year, assuming 12,000 miles are driven. However, this figure can be affected by driving style, weather, and road conditions.
Diesel engines have traditionally been the most fuel-efficient, offering nearly 90% better fuel economy than similar-sized gasoline, propane, or compressed natural gas (CNG) engines. However, newer technologies, such as the Detroit DD5 engine, can further improve fuel economy and lower fuel costs.
To calculate the fuel costs for a bus fleet, it is important to consider both the face value of fuel and fuel economy. The first step is to determine the fuel economy by dividing the number of gallons used by the mileage obtained. The second step is to calculate the total fuel cost by taking the total mileage per year and dividing it by the fuel economy to determine the number of gallons of fuel needed per year.
By improving the efficiency of public transit, such as through dedicated bus lanes, the ridership of buses can be increased, leading to a reduction in vehicle miles travelled (VMT), congestion, and fuel used by private vehicles. This, in turn, can help to reduce overall fuel costs and environmental impact.
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Fossil fuels and greenhouse gases
Fossil fuels, such as coal, oil, and natural gas, are the largest contributor to global climate change. When these fuels are burned to generate electricity and heat, they release carbon dioxide (CO2) and other greenhouse gases like methane (CH4), nitrous oxide (N2O), and hydrofluorocarbons (HFCs). These gases accumulate in the Earth's atmosphere, trapping the sun's heat and causing the planet to warm, leading to climate change.
The transportation sector is a significant contributor to greenhouse gas emissions, particularly from road vehicles that combust petroleum-based products like gasoline and diesel. In the United States, transportation accounts for about 28% of total greenhouse gas emissions, with emissions from buses, cars, trucks, ships, and planes all playing a role. Buses, for example, averaged 0.39 pounds of CO2 per passenger-mile in 2019, but this figure varies depending on the type of bus and its occupancy rate.
To reduce greenhouse gas emissions from transportation, several strategies are being implemented. These include the development of international carbon dioxide emissions standards for aircraft and the promotion of renewable fuels produced from plants, crops, and biomass. Additionally, the EPA and DOT have set emissions and fuel economy standards for vehicles, and programs like SmartWay help improve supply chain efficiency and reduce greenhouse gases in the freight transportation sector.
Public transportation, such as buses and trains, plays a crucial role in reducing greenhouse gas emissions. These modes of transport are more efficient than private cars as they can carry a larger number of people, resulting in lower emissions per passenger-kilometer. Upgrading bus fleets to run on clean electricity instead of fossil fuels can also significantly reduce emissions and improve air quality.
While fossil fuels are a major contributor to greenhouse gas emissions, it's important to recognize that other sectors, such as manufacturing, industry, and agriculture, also play a significant role in emitting these gases. The production of cement, iron, steel, electronics, plastics, and clothing, often using machines powered by fossil fuels, contributes to global emissions. Additionally, deforestation and land clearing for agriculture release stored carbon, further adding to the accumulation of greenhouse gases in the atmosphere.
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Energy usage and emissions
Fuel Choices and Their Impact:
The type of fuel used by buses has a significant impact on their energy usage and emissions. Traditionally, buses have relied on diesel fuel, which is a fossil fuel. Burning diesel releases carbon dioxide (CO2) and other greenhouse gases, contributing to climate change. However, there has been a growing trend to adopt cleaner alternatives, such as compressed natural gas (CNG). For instance, the KCATA (Kansas City Area Transportation Authority) has made strides in this direction, reducing their greenhouse gas emissions by 1,870 metric tons by switching to CNG. This move is equivalent to taking 395 passenger cars off the road for an entire year.
Passenger Load and Efficiency:
The energy efficiency of a bus is closely tied to its passenger load. A well-occupied bus can significantly reduce energy usage and emissions per passenger. For example, the average passenger load for a conventional bus in the US in 2006 was 9.22, resulting in 21.4 passenger-miles per gallon. In contrast, a typical passenger car with an average load of 1.58 passengers achieved 39.5 passenger-miles per gallon. However, it's important to note that bus occupancy rates can vary, with less popular routes and off-peak services having lower occupancy levels.
Calculating Emissions:
Calculating bus emissions can be complex, and various methods exist. One approach is to use a factor of 100g CO2 per person per mile for bus travel. The UK's Defra document calculates the average CO2 emission from buses as 0.089 kg per passenger km. Another calculation considers the total UK vehicle km by buses, resulting in a total CO2 emission of 4.3 million tonnes, or 0.07 tonnes per person per year. These calculations help put bus emissions into perspective.
Emissions in Context:
When discussing bus emissions, it's essential to compare them to other modes of transportation. Public transit buses are argued to dramatically reduce greenhouse gas emissions compared to private cars. The American Public Transit Association claims that public transit saves an estimated 1.4 billion gallons of gas annually, translating to about 14 million tons of CO2 reduction. However, critics like Thomas Rubin argue that such analyses may be distorted, and the environmental benefits of bus transit may not be as significant as claimed.
Overall, the energy usage and emissions of buses depend on a variety of factors, and continuous efforts are being made to improve their environmental footprint. Transitioning to alternative fuels, optimizing passenger loads, and implementing efficient technologies are all strategies to reduce the carbon footprint of bus transportation.
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Frequently asked questions
The amount of pollution caused by a bus depends on several factors, such as the type of fuel used, the number of passengers, and the distance travelled. On average, a typical bus in the US emits 21.4 passenger-miles of CO2 per gallon of fuel. In the UK, the average is 100g of CO2 emissions per person per mile for bus and coach travel.
Yes, taking the bus can help reduce pollution. Public transit saves an estimated 1.4 billion gallons of gas annually in the United States, which translates to about 14 million tons of CO2 emissions saved. This is because buses can carry more passengers than a typical car, so fewer vehicles are needed on the road.
According to a study, the average load in a typical passenger car in the US in 2006 was 1.58 passengers, resulting in 39.5 passenger-miles per gallon. In comparison, the average passenger load in a conventional bus during the same year was 9.22 passengers, resulting in 21.4 passenger-miles per gallon. This shows that buses can be more efficient in terms of emissions per passenger-mile.
Some bus systems are transitioning from diesel to compressed natural gas (CNG), which has environmental benefits. For example, KCATA in the US reduced its greenhouse gas emissions by 1,870 metric tons by switching to CNG fuel, which is equivalent to taking 395 passenger cars off the road for a year.
To calculate the carbon emissions of a bus, we need to consider the fuel consumption and the number of passengers. We can use the formula: Carbon emissions = Fuel consumption x Number of passengers x Emissions factor. The emissions factor is typically given in g of CO2 per person per mile or km.
