Human drivers in autonomous vehicles will monitor the system and be ready to resume control in ambiguous or emergency situations. As a driver's reaction time to intervene after having realized a problem has occurred can be critical, we present the Interactive Automation Control System (IACS) to assist the driver when their takeover is required. The system displays manual or automated mode in an unobstrusive location in the vehicle, signaling when a Take Over Request (TOR) is necessary. We evaluate the system's performance during a situation in which the automation has not been defined to operate and study its impact on the overall driving performance, specifically the driver's reaction time to a TOR. Results showed significant improvements in driving performance with the proposed system. Both the response time to the TOR and the number of collisions decreased when the IACS was activated. Subjective ratings of the system regarding its performance showed high satisfaction levels.