Trains are generally more energy-efficient than other modes of transportation, and they produce fewer emissions per passenger-mile. This is because trains can carry more passengers than cars or buses, and they are powered by electricity or diesel, which are cleaner fuels than gasoline.

Carbon dioxide (CO₂) is the primary greenhouse gas emitted by transportation activities, accounting for over 70% of total transportation-related emissions. CO₂ is produced when fossil fuels, such as gasoline and diesel, are burned for transportation purposes.

All of the listed policies are considered sustainable transportation policies because they aim to reduce the environmental impact of transportation. Encouraging the use of public transportation and promoting walkability and bikeability reduce the number of vehicles on the road, which leads to lower emissions. Investing in electric vehicle infrastructure supports the transition to cleaner transportation technologies.

Technology can contribute to reducing transportation-related emissions in various ways. Developing more fuel-efficient vehicles reduces the amount of fuel consumed per mile traveled. Promoting the use of renewable energy sources for transportation, such as electric vehicles, eliminates tailpipe emissions. Improving traffic management systems can reduce congestion and idling time, which also leads to lower emissions.

Water pollution is not typically considered a direct environmental impact of transportation. However, transportation activities can contribute to water pollution indirectly through runoff from roads and parking lots, which can carry pollutants into waterways.

Transportation transition is the term used to describe the shift towards more sustainable transportation systems. This transition involves moving away from reliance on fossil fuels and towards cleaner and more efficient transportation technologies and practices.

Airplanes generally have the highest environmental impact per passenger-mile because they consume more fuel and produce more emissions than other modes of transportation. This is due to the high energy requirements of air travel and the fact that airplanes operate at high altitudes, where emissions have a greater impact on the environment.

Nitrogen oxides (NO_x) are the primary air pollutant emitted by diesel engines. NO_x emissions are formed when nitrogen and oxygen in the air react at high temperatures during combustion. These emissions contribute to the formation of ground-level ozone and smog, which can have adverse effects on human health and the environment.

Internal combustion engine vehicles are not considered sustainable transportation technologies because they rely on fossil fuels, which contribute to greenhouse gas emissions and air pollution. Electric vehicles, hybrid vehicles, and fuel cell vehicles are all considered sustainable transportation technologies because they either produce zero emissions or significantly reduce emissions compared to internal combustion engine vehicles.

Induced traffic is the term used to describe the phenomenon where traffic congestion leads to increased emissions. This occurs when the construction of new roads or the expansion of existing roads leads to an increase in traffic volume, which in turn leads to higher emissions. Induced traffic can undermine the environmental benefits of transportation infrastructure projects.

Oxygen (O₂) is not a greenhouse gas. Greenhouse gases are gases that trap heat in the atmosphere, contributing to climate change. Carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) are all greenhouse gases emitted by transportation activities.

Sulfur oxides (SO_x) are the primary source of air pollution from ships. SO_x emissions are produced when sulfur-containing fuels, such as bunker fuel, are burned. These emissions can contribute to acid rain and respiratory problems.

Increased traffic congestion is not a benefit of sustainable transportation. Sustainable transportation aims to reduce traffic congestion by promoting more efficient and environmentally friendly transportation modes.

Vehicle reduction is the term used to describe the practice of reducing the number of vehicles on the road. This can be achieved through various strategies, such as promoting public transportation, walking, and biking, and encouraging carpooling and ride-sharing.

Abundance of fossil fuels is not a challenge associated with the transition to sustainable transportation. The transition to sustainable transportation aims to reduce reliance on fossil fuels and promote cleaner and more efficient transportation technologies.