根據美國國家研究委員會在18日所發布的報告指出，在2050年以前，也就是在37年內，美國小型車的溫室氣體排放量與汽油消耗量可以減少達80%。
撰寫報告的委員會主席蔡平（Douglas Chapin）表示，轉變並非一蹴可及，但結合高效能車輛；改用生質能、電能與氫氣以及強有力的政策等方式，可以克服高成本問題，並且影響消費者的決定。
蔡平是維吉尼亞MPR聯營公司首席政策分析與研究顧問，他表示，要達成這80%的目標「很困難，但並非不可能，只是需要有國家政策的強力支持。」他18日在電視記者會中表示，「即使目標沒有完全達成，部分的成功也可帶來好處。社會整體性的節約能源也是社會的福利。」
不過他也說，單純提高能源效率並無法在2050年以前達成目標。道路車輛的燃油效率必須達到每加侖180英里，根據報告中的說法，這是「現有科技下絕不可能的事情」。
因此，研究委員會也考慮了其他方案，像是油電混合動力車、插電式油電車、電動車、氫燃料電池電動車以及瓦斯車等。
委員會表示其所提出的數據是「探索與高度不確定性」的，但也同時指出，他們提出的節省能源成本、提升車輛科技、更佳的燃油經濟性以及溫室氣體減量等改變，都是值得市場投資，且效益高於市場本身的意願。
減少所有燃料的溫室氣體排放意味著在生產與使用這些燃料的時候，不能產生大量二氧化碳。委員會同時提出警告，要延長這類利用石化資源產生的電力，「就必須要成功的應用碳捕捉與儲存技術。」
雖然目前玉米酒精以及生質柴油是目前美國市場上唯一的生質燃料，研究委員會發現了一些源自木質纖維素的生質燃料是「更有具有潛力的」，包括一些農業廢棄物如麥桿、柳枝稷、整棵樹以及木材廢料。
委員會表示，這類來自「副產物」的生質燃料是設計用來替代汽油的，可以大量減少石油的使用以及溫室氣體排放量。導入使用這些燃料對現有輸送系統以及車輛並不會有重大影響。
報告中表示，結合使用高效能車輛以及足夠的纖維素生質燃油，可以在2050年以前達成減少石油消耗80%的目標。
當然，電動車不會排放任何溫室氣體，但也有其他無法推廣的阻礙。
委員會指出，電力的生產以及電網額外的負擔都是必須考量的因素。
至於到氫燃料電池車，委員會承認其唯一的排放物是水，並且表示這類車輛在2050年時應該會比先進的汽油車便宜。
但仍然會有問題。委員會警告說，協調發展氫氣基礎建設以及伴隨而來更多的燃料電池車輛將是「昂貴且困難」的。
委員會的報告表示，產生氫氣的過程中會排放溫室氣體，而低溫室氣體排放的製氫法過於昂貴，且需要進一步發展以提高競爭力。
報告表示，我們無法知道哪一個技術方法最後會獲得成功，這涉及了許多不確定因素。委員會相信，最好的辦法就是政府與業界共同促進對車輛與燃料研究的投資與發展，針對各項主要技術的問題，找出解決之道。
By the year 2050 – in less than 37 years – the United States could cut petroleum consumption and greenhouse gas emissions by 80 percent for cars and small trucks, finds a new National Research Council report released Monday.
There is no single "silver bullet," said chair of the committee that wrote the report, Douglas Chapin, but the shift can be made with a winning combination of more efficient vehicles; alternatives like biofuels, electricity, and hydrogen; and strong government policies to overcome high costs and influence consumer choices.
Chapin, who is a principal of the policy analysis and research consultancy MPR Associates of Alexandria, Virginia, said the 80 percent goal is "difficult but not impossible to meet if supported by strong national policy."
"Even if the goals are not completely met, partial success also produces benefits," Chapin told reporters on a telebriefing Monday. "Societal benefits mean energy saving for the community as a whole."
But improved efficiency alone will not meet the 2050 goals, he said. The average fuel economy of vehicles on the road would have to exceed 180 miles per gallon, which, the report says, is "extremely unlikely with current technologies."
So, the study committee also considered other alternatives such as hybrid electric vehicles, plug-in hybrids, battery electric vehicles, hydrogen fuel cell electric vehicles, compressed natural gas vehicles.
The committee calls its calculations "exploratory and highly uncertain," but says they indicate that the energy cost savings, improved vehicle technologies, better fuel economy and reduced greenhouse gas emissions are worth more than the costs of the transition over and above what the market is willing to do on its own.
Reducing greenhouse gas emissions for all fuels means they must be produced and used without large emissions of carbon dioxide. And, warned the committee, to the extent that fossil resources are used to generate electricity, "the successful implementation of carbon capture and storage will be essential."
While corn-grain ethanol and biodiesel are the only biofuels to have been produced in commercial quantities in the U.S. to date, the study committee found "much greater potential" in biofuels made from lignocellulosic biomass – which includes crop residues like wheat straw, as well as switchgrass, whole trees, and wood waste.
This "drop-in" biofuel is designed to be a direct replacement for gasoline and could lead to large reductions in both petroleum use and greenhouse gas emissions, the committee states. It can also be introduced without major changes in fuel delivery infrastructure or vehicles.
The report finds that enough cellulosic biomass could be produced by 2050 to meet the goal of an 80 percent reduction in petroleum use when combined with highly efficient vehicles.
Electric vehicles, of course, do not emit any greenhouse gases, but there are other barriers to their wider adoption.
The production of electricity and the additional load on the electric power grid are factors that must be considered, the committee points out.
Considering hydrogen fuel cell vehicles, the committee acknowledged that the only emission is water and said they could become less costly than advanced petrol-powered vehicles of 2050.
But there are problems here too. The committee warned that developing a hydrogen infrastructure in concert with a growing number of fuel cell vehicles will be "difficult and expensive."
Greenhouse gases are emitted during hydrogen production, and the low-greenhouse gas methods of making hydrogen are more expensive and will need further development to become competitive, the committee reports.
It is impossible to know which technologies will ultimately succeed, the report says, because all involve uncertainty. The committee believes that the best approach is to promote a portfolio of vehicle and fuel research and development, supported by both government and industry, designed to solve the critical challenges in each major candidate technology.
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