Federal law protects historically significant bridges, and any rehabilitation or improvement projects on them require special attention. Bridges designated as historic and listed or eligible to be listed in the National Register of Historic Places introduce a special railing challenge because the historic railing may not meet current standards. As soon as a project is determined to involve a historically significant bridge, the district should contact the TxDOT Bridge Division, as directed in the Bridge Division's Historic Bridge Manual. The director of the Texas Historical Commission is the designated State Historic Preservation Officer (SHPO) for Texas, and the SHPO and TxDOT are responsible for determining what effect any proposed project will have on a historic bridge.