Various proposals for High Speed rail passenger links are now being examined. These are generally State sponsored under Federal initiatives. Trains which may run on these lines in future could be operated by Amtrak or by other companies set up for the purpose.
To date, the only practical results of these developments has been the enhancement for High Speed running of the Northeast Corridor from Washington DC to Boston, operated by Amtrak. Planning for similar enhancements to the Southeast Corridor from Washington to Richmond VA, Charlotte NC and ultimately into SC and GA are at an advanced stage. Elsewhere, plans are mostly at an early stage and have varying degrees of local support.
This page lists a selection of projects for which information is available.
Flag image from CIA World Factbook