This paper proposes a roundabout controller that operates in a connected and automated vehicle (CAV) environment. The proposed controller bears the following features: (1) improves the mobility and capacity of roundabouts, (2) has the potential for real-world implementation, and (3) is easy to upgrade for partially connected and automated traffic. The proposed controller is evaluated against a conventional roundabout controller to quantify its performance. The results show that the proposed controller is able to improve throughput by approximately 14% and reduce delays ranging from 66% to 94%. The computational time of the proposed controller was demonstrated to be constantly less than 0.02 s across all traffic demands. This confirms the potential of the proposed controller for real-world application.