The average fuel economy of the cars and trucks on America's roads could reach 60 miles a gallon by the end of the next decade if automakers mass produced vehicles using hybrid and other advanced technologies, according to a report to be released Jan. 3 by the Union of Concerned Scientists (UCS). Using conventional technology, average fuel economy could reach 40 miles a gallon. Such vehicles would cost about $1,700 more but would save consumers $3,800 over the 15-year life of the vehicle, the UCS report found. In conjunction with the report's release, about 50,000 owners of hybrid vehicles are expected to rally outside the Los Angeles Convention Center today during the second day of media previews for the Los Angeles Auto Show.  Joined by actor and environmental activist Ed Begley Jr. and other celebrities, the participants will call on automakers to adopt hybrid technology across their product lines, according to the Detroit News.