The biggest challenge offered by autonomous vehicles is how cybersecurity, environmental sustainability, and system implementation all go hand in hand. Most of this research has already been well covered on each of the individual domains; however, the integration of security measures with sustainable practice into an Autonomous Vehicles (AV) system without hindering its operational efficiency is a significant gap in current understanding. This study employs a mixed-methods approach by conducting quantitative analysis on the pattern of energy consumption from 150 autonomous vehicles spread over three major urban centers, along with qualitative assessments of cybersecurity vulnerabilities and sustainable implementation frameworks. We have found that the traditional security protocols consume approximately 23% more energy on average, mainly because of increased computation overhead. However, we had reduced the energy consumption down to 47% as compared to the base setting, with the standards in NIST maintained with an adaptive encryption and power-aware intrusion detection system under GSA. This is supported by a lifecycle assessment stating the carbon footprint reduction percentage amount in AV infrastructure based on recycled components and renewable sources rather than the regular implementation. It concludes that security and sustainability in autonomous vehicles are not conflicting goals, providing a novel framework for manufacturers and policymakers to implement secure, sustainable AV systems while optimizing performance and resource utilization. Such findings significantly contribute to the evolving discourse on environmentally conscious autonomous transportation systems.