National Renewable Energy Laboratory (NREL):

February 18, 2014, 10am PST
So much for switching from diesel fuel to natural gas to protect the environment. A new report concludes that it is best to stick with oil-based fuels because methane leakage from natural gas is much greater than currently estimated.
The New York Times - U.S.
March 3, 2008, 11am PST
<p>In the San Francisco Bay Area, two public transit agencies are conducting trials with "Zero Emission Buses", or ZEBs. They are using different types of hydrogen fuel cell technologies, with very different results.</p>
San Jose Mercury News