Despite increasing interest in health and wellbeing in transport policy, there is no policy monitoring tools to measure the effects of street projects on the mental wellbeing of those who walk. After establishing the two types of wellbeing (subjective and eudaimonic), a review of the literature suggested four main ways streetscape environments can affect wellbeing: traffic domination, safety, pollution and street greenery. These were combined with urban design and journey satisfaction approaches to create 16 streetscape factors which were integrated into a theoretical framework conceptualising how streetscape experience influences wellbeing. Given its progressive Healthy Streets Approach to streetscape projects, London was the case study location chosen to test the framework. A comparative approach was taken, comparing wellbeing associated with streetscape factors at Archway, where a Healthy Streets project has been completed, and Stoke Newington where a project is planned. The results found that whilst there is broad agreement with the most and least important streetscape factors, there were differences in the exact ranking which comes out more significantly when these importance ratings were used together with actual experience to plot ‘disgruntlement’. Although no relationship was found with eudaimonic wellbeing, subjective wellbeing was positively related to journey experience with the subjective wellbeing element positive deactivation-negative deactivation most influenced by journey experience in both locations. The most significant journey experience factor was found to be ‘Easy to cross’. No mediating relationship was found with socio-demographic factors or visit frequency. The overall comparison of wellbeing between the two locations found a statistically significant relationship for positive deactivation-negative deactivation and a moderately significant for experience. Thus, it appears streetscape experience has a measurable impact on wellbeing so policymakers should turn their attention to including wellbeing in project appraisal.