Inductive loop detectors (ILD) systems have been employed on motorways to effectively monitor road traffic, providing insights for data-driven strategies for smart cities. However, traditional ILDs encounter several challenges, such as complex integration with other technologies, high installation costs, and demanding maintenance processes. To address these issues and create future-proof flexible traffic monitoring systems with high accuracy of current solutions, significant advancements in standard ILDs are crucial. This paper presents a new leaky-wave antenna on-road sensor, showcasing its efficient, and reliable monitoring and data collection which includes vehicle count, average speed, and lane changes. It utilises frequency-dependent beam scanning capabilities to explore multiple directions on the road without any physical movement. By intercepting electromagnetic waves emitted by vehicles from different angles, the proposed system efficiently processes this information to gain valuable insights into traffic behaviour and patterns. Initial experimentation in a simulated environment has validated the proposed solution, highlighting its robustness and accuracy, outperforming existing alternatives. The antenna-based sensor exhibits an efficiency surpassing 99% in simulations even in challenging simulations with random noise figures and effectively captures 98% of lane changes. Additionally, the system provides real-time insights into road conditions with minimal operational and capital expenses compared to previous approaches. This innovation will make a valuable contribution to the progress of smart cities and the successful deployment of CAVs. By leveraging the potential of electromagnetics, this research aims to enhance efficient traffic data collection, ultimately fostering safer and more efficient transportation systems.