NASA recently completed the N+3 program for advanced concepts and technologies for airliners that would go into service in the 2030-35 timeframe. The program studied both subsonic and supersonic airliners. The goal of the subsonic program was to reduce fuel burn by 70%, NOx emissions 75% and airport noise 71dB by 2030-35. Four teams participated in the study: Boeing, Northrop Grumman, The Massachusetts Institute of Technology, and General Electric/Cessna.
Source: http://www.aviationweek.com/aw/blogs/aviation_week/on_space_and_technology/index.jsp?plckController=Blog&plckBlogPage=BlogViewPost&newspaperUserId=a68cb417-3364-4fbf-a9dd-4feda680ec9c&plckPostId=Blog%3Aa68cb417-3364-4fbf-a9dd-4feda680ec9cPost%3Ac906b912-4f2d-4e83-8331-ed59fa188034&plckScript=blogScript&plckElementId=blogDest
Source: http://www.aviationweek.com/aw/blogs/aviation_week/on_space_and_technology/index.jsp?plckController=Blog&plckBlogPage=BlogViewPost&newspaperUserId=a68cb417-3364-4fbf-a9dd-4feda680ec9c&plckPostId=Blog%3Aa68cb417-3364-4fbf-a9dd-4feda680ec9cPost%3Ac906b912-4f2d-4e83-8331-ed59fa188034&plckScript=blogScript&plckElementId=blogDest