Mineta Report Says Car Sharing Does Lower GHG Emission Impacts

The Mineta Transportation Institute (MTI) has released "Greenhouse Gas Emission Impacts of Car Sharing in North America," the results of a study that evaluated the greenhouse gas (GHG) emission changes that can occur when people participate in car-sharing organizations.

Principal investigators were Elliot W. Martin, Ph.D., and Susan A. Shaheen, Ph.D.

The research showed that, while car sharing does facilitate lower emissions, the reduction cannot be generalized across all participating individuals or even a majority of those individuals. Rather, car sharing as a system facilitates large reductions in the annual emissions of some households, which compensates for the collective small emission increases of other households. The results also show that respondent households significantly reduced vehicle ownership after joining car sharing.

“Car sharing is a simple concept,” said Martin. “People typically access vehicles by joining an organization that maintains a fleet of cars and light trucks deployed in lots located within neighborhoods, public transit stations, employment centers, and colleges or universities. They benefit from private vehicle use without the costs and responsibilities of ownership. Car sharing is most common in major urban areas where transportation alternatives are easily accessible.”

In this study, the authors surveyed car sharing members in the United States and Canada to develop a robust estimate of GHG emission impacts from car sharing. The research results illustrate the annualized change in GHG emissions among members within the largest car sharing organizations. These emissions are lower due to car sharing. The average change in emissions across all respondents is -0.58 t GHG per household per year for the observed impact, and -0.84 t GHG per household per year for the full impact.

While it may seem logical that car sharing reduces emissions, it also can increase them because it provides automotive access to people who were previously car-less. These households drive more than before they joined car sharing. The researchers took these factors into account when coming to a “net effect” conclusion across the 6,281 respondents that were applied in the final analysis. They also included less-obvious “full impact” factors, such as people who would have purchased a car but joined a car sharing group instead.

The authors found that on balance, net car sharing emissions are negative and statistically significant for both the observed impact and full impact. Hence, GHG emissions from transportation are lower due to car sharing.
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