Trains are generally considered to be the most environmentally friendly mode of transportation because they produce less emissions per passenger than cars, buses, and airplanes.

Carbon dioxide is the primary greenhouse gas emitted by transportation, accounting for over 70% of total emissions.

Noise pollution is not a negative environmental impact of transportation, as it does not directly harm the environment.

Transportation sustainability is the term for the process of reducing the environmental impact of transportation.

Building more roads is not a strategy for reducing the environmental impact of transportation, as it can lead to increased traffic and emissions.

Urban sprawl is the term for the phenomenon of urban areas becoming more spread out and less dense.

Increased biodiversity is not a negative environmental impact of urban sprawl, as it can lead to a more diverse and resilient ecosystem.

Exurbanization is the term for the phenomenon of people moving from urban areas to rural areas.

Reduced traffic congestion is not a positive environmental impact of exurbanization, as it can lead to increased air pollution and greenhouse gas emissions.

Exurban commuting is the term for the phenomenon of people living in rural areas but commuting to urban areas for work.

Increased land pollution is not a negative environmental impact of exurban commuting, as it does not directly harm the environment.

Urban-rural commuting is the term for the phenomenon of people living in urban areas but working in rural areas.

Reduced land pollution is not a positive environmental impact of urban-rural commuting, as it does not directly benefit the environment.

Suburban commuting is the term for the phenomenon of people living in suburban areas but commuting to urban areas for work.

Increased water pollution is not a negative environmental impact of suburban commuting, as it does not directly harm the environment.