This paper presents the design and experimental implementation of an integrated longitudinal and lateral control system for the operation of automated vehicles in platoons. The design of the longitudinal control system include nonlinear vehicle dynamics, string-stable operation with very small inter-vehicle spacing, operation at all speeds from a complete stop to high-speed cruising, and the execution of longitudinal split and join maneuvers in the presence of communication constraints. The design of the lateral control system include high-speed operation using a purely "look down" sensor system and lane changing without transitional lateral position measurements. We also describes the design of an on-board supervisor that utilizes inter-vehicle communication and coordinates the operation of the lateral and longitudinal controllers in order to execute entry and exit maneuvers. Experimental results are included from the NAHSC demonstration of automated highways at San Diego, CA.