Trains are the most energy-efficient mode of transportation, producing significantly less carbon dioxide emissions per passenger-mile than cars, buses, and airplanes.

Carbon dioxide (CO2) is the primary greenhouse gas emitted by transportation, accounting for over 70% of the sector's total emissions.

Fuel efficiency is a measure of how much fuel a vehicle consumes per unit of distance traveled. Higher fuel efficiency means that the vehicle emits less carbon dioxide per mile, resulting in a lower carbon footprint.

Traffic congestion is a result of inefficiencies in the transportation system, such as road design and traffic management. While it can lead to increased fuel consumption and emissions, it is not a direct contributor to the carbon footprint of transportation.

Individuals can reduce their carbon footprint from transportation by using public transportation or carpooling, walking or biking for short distances, choosing fuel-efficient vehicles, and avoiding unnecessary trips.

Carbon footprint is a term used to describe the total amount of greenhouse gases produced by a product or service over its entire life cycle, from extraction of raw materials to disposal.

Airplanes have the highest carbon footprint per passenger-mile compared to other transportation modes due to the high fuel consumption and emissions associated with air travel.

Fossil fuels, such as gasoline and diesel, are the primary source of energy for most vehicles, contributing to the majority of transportation-related carbon emissions.

Heavier vehicles require more energy to move, resulting in higher fuel consumption and carbon emissions.

Carbon intensity is a term used to describe the amount of greenhouse gases emitted per unit of distance traveled, typically measured in grams of carbon dioxide equivalent per kilometer.

Vehicle type has the greatest impact on the carbon footprint of a vehicle, as different types of vehicles have varying levels of fuel efficiency and emissions.

Governments can reduce the carbon footprint of transportation by investing in public transportation, promoting fuel-efficient vehicles, implementing carbon pricing, and encouraging walking and biking.

Diesel engines emit significant amounts of black carbon, a type of particulate matter that contributes to climate change and air pollution.

Higher speeds result in increased fuel consumption and emissions, leading to a higher carbon footprint.

Trains have the lowest carbon footprint per ton-mile compared to other transportation modes due to their high energy efficiency and ability to transport large quantities of goods.