Accelerated vehicle retirement is recognized as crucial for managing fleet emissions effectively. However, the emergence of new energy vehicles introduces complexities in assessing their environmental impacts. This study developed a dynamic fleet-based life cycle assessment model to analyze the effects of four distinct scrappage strategies in China from 2021 to 2060. The results underscore the importance of a meticulously chosen retirement strategy that harmonizes fleet characteristics with advancements in vehicle technology to promote sustainable mobility. Accelerated retirement strategies are demonstrated to enhance vehicle sales and expedite the incorporation of new energy vehicles into the fleet. Although these policies reduce greenhouse gas and carbon monoxide emissions, they may exacerbate other air pollutants, necessitating vigilant management. Additionally, the temporal distribution of environmental impacts reveals the critical need for long-term assessments. By evaluating six negative externalities of emissions, the research indicates that targeted scrappage policies, which advocate for the retirement of older vehicles, could potentially generate economic benefits of 6.81 to 7.29 billion dollars in reduced losses. However, an overly aggressive scrappage policy could increase negative externalities, leading to additional costs ranging from 0.84 to 3.31 billion dollars. This study reveals the intricate long-term environmental consequences of scrappage strategies accompanying the rise of new energy vehicles and lays a methodological groundwork for ongoing research into the most effective retirement scheme.