A group sponsoring the development of alternative power sources for commercial vehicles believes diesel engines will start to lose their dominant position in the heavy-truck market in seven years. According to a market forecast developed during the Third Annual Clean Heavy-Duty Vehicles Conference in Arizona last month, diesel engines will power less than 80% of new heavy-duty vehicles sold by the year 2010 from near 100% today. By 2020, only 66% of the new heavy-duty trucks may be powered by diesel engines, according to opinions gathered by WestStart-CALSTART, the conference's organizer. The group also forecast that by 2010, natural gas engine systems are projected to account for 10% of the market, hybrid systems for another roughly 10%, with fuel cell systems somewhere under 2%. By 2020, natural gas is projected to power over 11% of new heavy trucks, with hybrids projected to power another 17% and fuel cell systems to as much as 6% of the new heavy trucks. According to experts polled by WestStart-CALSTART at the conference, emission requirements and fuel costs are the top reasons why heavy-duty truck buyers will move away from diesel engines by 2010, followed by energy security issues and global warming. By 2020, respondents believe fuel costs will emerge as the primary issue motivating change, WestStart-CALSTART said. The fleets most likely to adopt natural gas and hybrid systems in 2010, the group added, are urban refuse trucks, urban delivery trucks and transit buses. Also, on the fuel side, respondents projected that gas-to-liquid or synthetic diesel formulations would make up 5-10% of the 2010 market for diesel fuels, with biodiesel representing less than 5%. By 2020, the market share for each of these is expected to rise to near 10%.