Government Scientific and Technical Resources (US Portal)
http://www.scitechresources.gov/

Office of Pipeline Safety (U.S. Department of Transportation)
http://ops.dot.gov

National Institute of Standards and Technology (NIST)
http://www.nist.gov/

NIST On-line Databases at
www.nist.gov/srd/online.htm

U.S. Department of Transportation
(includes links to Federal Aviation Administration, Federal Highway Administration, etc.)
www.dot.gov/

The National Transportation Safety Board
(includes Pipeline and Hazardous Material section)
www.ntsb.gov

Transportation Safety Institute - Pipeline Safety Division - U.S. Department of Transportation
http://www.tsi.dot.gov/divisions/pipeline/pipeline.htm
(click on PEPG for information on operator qualification rule)