What standards apply to newly constructed and altered facilities covered by the ADA?

Effective March 15, 2012, the applicable standards for new construction and alterations for either a public entity under Title II or a place of public accommodation under Title III are the 2010 ADA Standards for Accessible Design. In addition, transportation facilities are covered by the Department of Transportation’s 2006 ADA Standards for Transportation Facilities. You can find the combined standards here: https://www.access-board.gov/ada/

For additional information, take a look at the following resources:

FAQ: Where can I find a complete set of ADA standards for accessible design?