The following sites provide general histories on transportation, engineering and related fields.

http://www.fhwa.dot.gov/infrastructure/history.htm
Federal Highway Administration history of roads and infrastructure in the United States

http://www.olmsted.org/parks
National Association for Olmsted Parks, information on Olmsted designed parkways

http://www.usda.gov/history2/text6.htm
General information on American transportation history

http://isweb.tasc.dot.gov/Historian/historian.htm
Information on American transportation history

http://inventors.about.com/library/inventors/bl_history_of_transportation.htm
General transportation history

http://lcweb2.loc.gov/ammem/award97/mhsdhtml/aladAuthors1.html
Examples of work by prominent American landscape architects and designers

http://www.tfhrc.gov/pubrds/janfeb02/exhibition.htm
Transportation paintings by Bureau of Public Roads artist Carl Rakeman