Public Private Partnerships are increasingly used to deliver infrastructure, but the existence of a formal framework does not necessarily guarantee effective project performance. This study examined how the legal, contractual, financial, and risk allocation frameworks were associated with the performance of the Nairobi Expressway. A convergent parallel mixed methods design was adopted. The target population comprised 240 professionals from the PPP Directorate, the Kenya National Highways Authority, and Moja Expressway Company. Stratified purposive sampling was used, with a target sample of 160 respondents and 149 completed questionnaires included in the final analysis. Data were collected using a structured questionnaire containing 16 closed ended Likert scale items and eight open ended prompts. Quantitative data were analysed using descriptive statistics, Cronbach’s alpha, Pearson correlation, and multiple linear regression, while qualitative responses were independently verified and analysed thematically. The contractual framework had the strongest association with project performance, r = .804, p < .001, and the strongest unique regression contribution, β = .377, p < .001. The financial and risk allocation frameworks also made significant unique contributions, while the legal framework did not make a significant unique contribution after the other predictors were controlled. The regression model explained 74.0% of the variation in project performance. The study recommends stronger operational guidance, clearer contractual obligations, more predictable financial arrangements, active risk monitoring, and independently verified performance reporting.