This study investigates the impact of emissions-based taxes, specifically bonus/malus schemes, on the retirement of older and inefficient vehicles. Focusing on Switzerland's cantons, we utilize a difference-in-differences design within a survival analysis framework to analyze the effects of three distinct bonus/malus schemes. The study's unique contribution lies in its focus on the retirement of existing vehicles, rather than new vehicle sales, providing crucial insight into the unintended consequences of emissions-based tax policies on the overall vehicle fleet. We find that a retroactive malus, applied to both new and existing vehicles, can accelerate retirement, while a prospective malus, applied only to new vehicles, may postpone retirement. These findings highlight the importance of considering the entire vehicle stock when designing emissions-based tax policies to ensure their effectiveness in reducing emissions.