Tennøy has engaged with land use and transport planning and development for more than 20 years, as a planner and researcher. She is highly knowledgeable in, and has carried out research on, effects of land use and transport developments on transport, environment and society, the planning and decision-making institutions, systems and processes, as well as instruments and methods used in land use planning and transport planning.
The main research interest is strategic land use and transport planning, often under headings such as sustainable urban development, traffic reducing land use and transport development, and attractive and climate friendly cities.