under which act was it constructed?
Federal Aid Highway Act of 1956.
Interstate Highway System
The Dwight D. Eisenhower National System of Interstate and Defense Highways, commonly known as the Interstate Highway System, is a network of controlled-access highways that forms part of the National Highway System in the United States. Construction of the system was authorized by the Federal Aid Highway Act of 1956. 
what is interstate 296? A part of the Interstate Highway System in the US state of Michigan. can you name any two states it connects? I-196 near downtown Grand Rapids and I-96 on the north side of Grand Rapids in Walker. when was it opened? In December 1962.
wiki:11578581
Interstate Highway System [SEP] Introduction
The Dwight D. Eisenhower National System of Interstate and Defense Highways, commonly known as the Interstate Highway System, is a network of controlled-access highways that forms part of the National Highway System in the United States. Construction of the system was authorized by the Federal Aid Highway Act of 1956. The system extends throughout the contiguous United States and has routes in Hawaii, Alaska, and Puerto Rico. The U.S. federal government first funded roadways through the Federal Aid Road Act of 1916, and began an effort to construct a national road grid with the passage of the Federal Aid Highway Act of 1921.