Charles Dwight (Cap) Curtiss, 95, commissioner of the old U.S. Bureau of Public Roads in the mid-1950s, who administered and helped initiate construction of the $50 billion interstate highway system, died June 9 in a retirement home in Medford, N.J., after a heart attack.

Mr. Curtiss moved here and joined the Bureau of Public Roads, a precursor of the Federal Highway Administration, in 1919. He was an engineer and administrator and an authority on highway finance and management. He was head of the bureau for two years before retiring in 1957. The interstate highway system he administered was the largest joint federal-state public works program in U.S. history.

After leaving the government, he was a consultant to both the International Road Federation and the American Road Builders Association and was chairman of the old Highway Research Board, before retiring a second time in 1968. He moved to New Jersey in 1971.

He was a 1951 recipient of the Commerce Department's exceptional service gold medal award. He was a life member of the American Society of Civil Engineers, and was secretary of its highway divison from 1923 to 1947. He also served as president of the society's national capital section in the 1940s. He was an honorary member of the Institute of Traffic Engineers and a member of the Cosmos Club.

Mr. Curtiss was born in Camden, Mich., and was a 1911 gradute of Michigan State University. He earned a master's degree from Columbia University, and a degree in civil engineering from the old Iowa State College. He served with the Army in Europe during World War I, attaining the rank of captain.

His wife, the former Dorothea Davis, died in 1980. His survivors include a son, Charles Dwight, of Cincinnati; a daughter, Martha Trate of Fort Lauderdale, Fla.; four grandchildren, and five great-grandchildren.