California is often portrayed as a global leader in environmental policy, yet its transportation sector remains the state's largest source of greenhouse gas emissions and a persistent obstacle to meeting climate targets. This article argues that this contradiction can only be understood through a long-term historical analysis of California's transportation system. Focusing on the period from the late 1940s to the 2020s, it traces how post-war infrastructure investment, automobility, suburbanisation, and growth-oriented policy frameworks produced enduring patterns of high mobility demand, material throughput, and environmental overshoot. Combining quantitative indicators with qualitative analysis of policies, institutions, and socio-technical imaginaries, the study uses the Safe and Just Space framework as an analytical lens to assess the sustainability of transport trajectories over time. It shows that successive waves of environmental regulation and technological innovation mitigated specific impacts without altering the structural drivers of car dependence. The article concludes that California's transport challenges are historically embedded and that achieving deep sustainability will require confronting these long-standing structural dynamics.
