Mass transit options are more eco-friendly overall than large numbers of private vehicles, and, as mass transit options grow, they have revolutionized travel habits and continue to reduce single-occupancy commuting. Shuttle services in and out of large cities can help reduce peak-hour congestion, parking problems, and air pollution. Shuttles such as a Houston airport shuttle bus even help to decrease traffic congestion and delays at airports, large resorts, and convention centers.
Using data from the U.S. Environmental Protection Agency and the U.S. Department of Energy, one can see the CO2 emissions and average fuel mileage of shuttle buses and cars. If you divide those on a per-passenger basis, you can see that shuttles for group transportation cause far less pollution than single commuters or even ridesharing options.
It is also becoming more common for travelers to reduce their carbon footprint when traveling for vacations. Using options like a Houston airport shuttle bus is one of many options for helping to reduce CO2 emissions while traveling for leisure. All in all, no one disputes that a single car is better for the environment than a shuttle bus; however, when multi-user transportation is involved, shuttle buses are the greener option by far.