This paper proposes a degree-of-priority based control strategy for emergency vehicle preemption operation to decrease the impacts of emergency vehicles on normal traffic. The proposed model features its effectiveness to the following three aspects: (1) a multilayer fuzzy model was established to determine the degree-of-priority based on emergency vehicle preemption demand intensity and preemption influence intensity; (2) for emergency vehicles with proper classification, a travel time estimation model for emergency traffic was formulated, an optimal emergency route determines model based on the level of priority of emergency events, and the emergency vehicle travel time was developed to minimize evacuation time as well as minimize the adverse impacts of preemption on normal traffic; and (3) a conditional traffic signals priority control method at each intersection of the evacuation route was built, so that traffic queue at each intersection can be cleared before the arrival of emergency vehicles. A simulation model based on field data was developed, and the performance of the proposed strategy was compared with the conventional local detection based method under the microscopic simulation model. The results validated the efficiency of the proposed strategy in terms of minimizing the delay of emergency vehicles and reducing adverse impacts on normal traffic. 1. Introduction Providing safe and fast driving environment for emergency vehicles to reduce travel time and delay is a critical issue in traffic evacuation. Under effective preemption, ones can reach their destinations at the earliest possible time which is one of most critical factors in saving lives and reducing property loss. At the same time, reducing the adverse impacts of emergency vehicles on normal traffic, so that they can cause the least disturbance to network traffic flow, is the key to avoid the grid-lock caused by emergency accidents [1, 2]. While substantial progress has been made in the areas of vehicle detection and communication technologies to increase the efficiency of emergency vehicles, current state-of-the-art in signal preemption in China has not reached the point where signal clearance strategy, considering the adverse impact or normal traffic, can be automatically generated and implemented in real time. To date, most preemption systems developed operate on a single-intersection basis and require local detection of an emergency vehicle to activate a signal preemption sequence at each intersection [3, 4]. Existing signal preemption methods can be classified into several
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