The addition of gasoline to diesel could improve diesel engine efficiency.
Atlanta leads the nation.
European Union criticizes Germany for evading environmental rule.
Stricter emissions standards have created a new market, but questions remain about alternative fuels.
Some key differences in maintenance practices between CNG- and diesel-powered heavy trucks.
Test driving a CNG-powered tractor pulling a loaded trailer.
The Tesla S all-electric sports sedan is in many ways ahead of its time.