This article describes the design of a transdisciplinary project termed Te Ara Mua-Future Streets, intended to integrate community, policy and research knowledge and assess a range of outcomes. It is an area-level randomised, controlled before-after intervention study based in Auckland and aims to assess the effect of retrofitting street changes at the suburb scale on multiple health, social and environmental outcomes. The study is focusing particularly on identifying factors that improve walking and cycling to local destinations in low-income neighbourhoods and on reducing social and health inequities experienced by Māori and Pacific people. Qualitative system dynamics modelling was used to develop a causal theory for the relationships between active travel, walking and cycling infrastructures. Auckland Transport, the regional transport planning and investments authority, helped to develop the project and committed to funding the intervention construction. Auckland Transport and the study researchers have triangulated best evidence from the literature, transport policy makers, urban design professionals and community knowledge to develop interventions that were contextually and culturally appropriate. Direct observation and random sample face-toface surveys are measuring a wide range of objective outcome measures: road-user behaviour, changes to travel mode for short trips, physical activity, air quality, road traffic injuries, greenhouse gas emissions, and perceptions of neighbourhood social connection, safety, and walking and cycling infrastructure.