The Valley Transportation Authority and SamTrans on Monday will begin a three-year program to test the viability of zero-emission fuel-cell bus technology. The agencies will operate three buses powered solely by hydrogen to comply with new regulations by the California Air Resources Board to reduce nitrogen oxide and particulate matter.

The agencies are the first in the Bay Area to test the new fuel technology. The tailpipes from these buses will emit wisps of water vapor instead of plumes of diesel exhaust, which is linked to numerous respiratory ailments. The change may reduce soot emissions by 90 percent.

The VTA's goal is to convert 15 percent of its buses from diesel to zero-emission buses over several years.

The exact technology to reach zero-emission levels can vary, and federal officials are not ready to commit to one method. The program will test whether a $3 million bus operated by fuel cells can withstand the daily pounding of traffic and loading of thousands of passengers a day.