Advancements in technologies enabling greater use of electric or alternative fuel vehicles will continue to impact gas tax revenues. The U.S. Energy Information Agency estimates that fuel efficiency for all light-duty vehicles (cars and light trucks) will steadily increase, from an average weighted MPG of just over 20 in 2010 to over 36 in 2040. The fuel efficiency of freight trucks also is expected to improve, although at a slower rate, from an average weighted MPG of over 6 in 2010 to over 8 in 2040. This projection assumes there is not a major paradigm shift in vehicle fuel technology, such as affordable electric cars or hybrid heavy-duty trucks. It also assumes no shift will occur in public policy or public attitudes that encourage people to reduce their long-term travel habits or shift to more efficient vehicles more quickly. Given the growing concern about climate protection and fuel price volatility, however, such changes are likely, which would lead to a more rapid deterioration in the long-term viability of the current fuel tax.