P. Robert Knaff, 69, a former Transportation Department traffic specialist who was involved in research that led to the adoption of the centered, high-mounted tail light now required on all cars, died Aug. 25 at his home in Silver Spring after a heart attack.

Dr. Knaff worked for the U.S. Transportation Department from 1970 to 1986, including 12 years as director of driver and pedestrian research for the National Highway Traffic Safety Administration. In that capacity, he devised and led human factors research programs that influenced vehicle designs.

After retiring from the Transportation Department in 1986, he became a co-founder, technical director and chief scientist of KB & A Inc., a traffic and product safety firm in Silver Spring.

He was a native of New York City and graduated from Champlain College in Burlington, Vt. He received a master's degree in experimental psychology from McGill University in Montreal and a doctorate in human factors engineering from the University of Maryland.

Dr. Knaff was a research psychologist at the Air Force Cambridge Research Center in the late 1950s, and he later worked as a consultant and group leader in engineering psychology for private companies providing support to NASA's manned space flight programs.

He was a member of the Human Factors and Ergonomics Society and the Society of Automotive Engineering.

His marriage to Rhoda Knaff ended in divorce.

Survivors include his wife, Karen D. Knaff of Silver Spring; three children from his first marriage, Constance Bell of Tucson, Jennifer Knaff of Austin and Donna Knaff of Albuquerque; a stepson, Eric Bunting of Derwood; and five grandchildren.