To achieve automation in Intelligent Transportation System (ITS) environments, it is preferred that integrations for existing traffic management systems as well as various vehicle-centered systems can be done without major modification. This is in particular essential for an automated emergency vehicle preemption system, where traffic signal preemption should be more accurate, smooth, and safe. Current researches for ITS middleware do not give much thought on interoperability and performance. Thus they cannot support such automation framework. This paper proposes Bevor, an ITS middleware for emergency vehicle preemption based on National Transportation Communications for ITS Protocol (NTCIP). By utilizing NTCIP protocols in Communication Layer, Bevor achieves communication and data interoperability across most devices and equipments. The deployment of NTCIP STMF also significantly improved the effectiveness of transmission. The Service Layer of Bevor is designed with the Web 2.0 framework and XML exchange, enabling easy access to data as well as operations such as event detection, policy matching, etc. A prototype system was implemented, and the experimental results show that Bevor offers a great interoperability, more flexible automation control, reuse, and improved performance.