A History Department member since 1967, in 1990 he became the Richard S. Caliguiri University Professor of Urban and Environmental History and Policy, a position he still holds as Professor Emeritus.
His research includes environmental and urban development and systems and their effects.
During his tenure at Carnegie Mellon, Tarr held, at various points, the positions of head of the Department of History, Acting Dean of the Dietrich College of Humanities and Social Sciences, Acting Dean of the School of Urban and Public Affairs, director of the Program in Technology and Society, and co-director of the Program in Applied History and Social Science.
[3] Tarr co-authored a book in 2007 with Clay McShane titled, Horse in the City: Living Machines in the Nineteenth Century.
[4] In 1989, Tarr received the Abel Wolman award from the American Public Works Association for his book titled Technology and the Networked City in Europe and America (co-edited with Gabriel DuPuy).