Civil and environmental engineering

A great list of data sources, including those below.

US Dept of Transportation. Bureau of Transportation Statistics.
National overview of infrastructure, traffic, energy, environmental and economic data relating to transportation. Includes DOT and non DOT data.

US Energy Information Administration (EIS).
See topic: Transportation for all available tables. Good place for fuel data.

US Dept of Transportation, Bureau of Transportation Statistics.
Over 100 databases of transportation statistics searchable in one database. Provides raw data.

US Dept of Transportation, Federal Highway Administration

U.S. Dept of Energy, ORNL.

US Dept of Transportation, NHTSA.
Details factors behind traffic fatalities.