The interplay between autonomous and manual vehicles in mixed traffic situations is a matter of concern as it may significantly affect the overall performance of the transportation system. Furthermore, two critical issues must be addressed: the transportation system's energy consumption and environmental impact. A more profound comprehension of mixed traffic dynamics, where autonomous and human-driven cars coexist, is necessary to navigate the transition from current conditions to an ecosystem entirely dominated by autonomous vehicles. To tackle these issues, this article aims to develop eco-driving approaches that reduce environmental effects and enhance energy efficiency. The case study under consideration is a roundabout with heavy traffic, and it examines how the total number of vehicles exiting the roundabout varies based on multiple input criteria. As a result, it was noted that the quantity and manner in which autonomous vehicles enter the roundabout from the priority road could affect the number of traditional vehicles that enter the yielding road. Increasing traffic flow in the roundabout can mean less fuel consumed and reduced emissions. To simulate the traffic in the roundabout, a model was developed in the MATLAB® program, and the actors, which are autonomous or classic vehicles characterized by functional characteristics, ran in various scenarios to determine optimal solutions for smoothing the traffic.