The advancement of 6G technology has the potential to revolutionize the transportation sector and significantly improve how we travel. 6G-enabled Intelligent Transportation Systems (ITS) promise to offer high-speed, low-latency communication and advanced data analytics capabilities, supporting the development of safer, more efficient, and more sustainable transportation solutions. However, various security and privacy challenges were identified in the literature that must be addressed to enable the safe and secure deployment of 6G-ITS and ensure people's trust in using these technologies. This paper reviews the opportunities and challenges of 6G-ITS, particularly focusing on trust, security, and privacy, with special attention to quantum technologies that both enhance security through quantum key distribution and introduce new vulnerabilities. It discusses the potential benefits of 6G technology in the transportation sector, including improved communication, device interoperability support, data analytic capabilities, and increased automation for different components, such as transportation management and communication systems. A taxonomy of different attack models in 6G-ITS is proposed, and a comparison of the security threats in 5G-ITS and 6G-ITS is provided, along with potential mitigating solutions. This research highlights the urgent need for a comprehensive, multi-layered security framework spanning physical infrastructure protection, network protocol security, data management safeguards, application security measures, and trust management systems to effectively mitigate emerging security and privacy risks and ensure the integrity and resilience of future transportation ecosystems.