0018-9545 (c) 2017 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TVT.2017.2784568, IEEE Transactions on Vehicular Technology 1 WSN-EVP: A Novel Special Purpose Protocol for Emergency Vehicle Preemption Systems Mohamed Masoud, Student Member, IEEE, and Saeid Belkasim, Member, IEEE Abstract—Emergency Vehicle Preemption (EVP) systems play a key role in reprioritizing signalized traffic intersections. This role is important for safe and minimum travel delay of Emergency Vehicles (EV) passing through road intersections. Unfortunately, conventional systems that are currently in use on the roads have deficiencies in terms of cost, reliability, maintainability, and scalability. In this paper, a novel approach is proposed utilizing batteryless Wireless Sensor Networks (WSNs) to overcome the above difficulties and improve the safety and mobility of emergency vehicles. A special purpose preemption protocol is designed based on the Collection Tree Protocol (CTP) as a data collection service. The protocol is called WSN-EVP and is used to handle the EV preemption request in a multi- hop tree-based topology spread across the traffic intersection. The model functions according to predefined rules and optimized parameters to cope with the high topology changes and the fast response time requirement. A prototype implementation using TelosB motes programmed in nesC shows a performance of high preemption accuracy under high level of interference. Index Terms—Wireless sensor networks (WSNs), emergency vehicle preemption (EVP), collection tree protocol (CTP). I. I NTRODUCTION EVP systems main function is to reprioritize signalized traffic intersections. The reprioritization process allows Emer- gency Vehicles (EVs) (e.g. ambulances, firefighting and po- lice) to have the right-of-way at traffic intersections. This emergency preemption procedure is imperative for providing safe travel and fast arrival of EVs to their destinations. The U.S. Department of Transportation (DOT) reported that the number of EV crashes in signalized intersections showed a significant reduction with the installation of EVP systems [1]. For instance, in Plano city, Texas, the installed EVP systems decreased the EV crashes from 2.3 per year to less than 1 intersection crash every five years [2]. Another advantage of EVP systems is the reduction of EV travel time to its destination. This time has an important impact especially in the case of rescuing critical medical conditions and saving lives. According to the cardiac arrest survival factor, each delay of one minute reduces the chance of survival by 7-10%, and there is a little chance of survival after 8 minute delay [3]. In firefighting situations, every delay of 30 seconds in reaching the destination will result in doubling the fire size [4]. In 2015, there were 1,345,500 fires reported in the US. These fires caused 3,280 civilian deaths and $14.3 billion in property damage [5]. These facts point to the necessity of improving and expanding the use of EVP systems. Copyright (c) 2015 IEEE. Personal use of this material is permitted. However, permission to use this material for any other purposes must be obtained from the IEEE by sending a request to pubs-permissions@ieee.org. M. Masoud, and S. Belkasim are with the Department of Computer Science, Georgia State University, Atlanta, GA, 30302 USA e-mail: mma- soud1@student.gsu.edu; sbelkasim@gsu.edu. Even though both of EVP systems and vehicular networking applications share the same concept of vehicle-infrastructure communication, the EVP workflow model uses different un- derlying technologies and communication methods. Basically, the EVP model consists of three main consequent phases: Detection, preemption and transition. When an EV preemp- tion request is detected by the system sensor, the system controller will grant the right-of-way to the approaching EV and then waits till the EV passes through the intersection before returning the traffic signals to their normal operation. Classification of the EVP systems depends on the sensor type used in the detection phase (e.g., siren, GPS, etc.). However, current EVP systems are costly and have multiple limitations. More elaboration on the deficiencies of current systems is given in more details in next section. In order to improve current EVP systems, we propose a novel WSN-based approach that satisfies the standard system requirements [6]. Our contributions are summarized as follows: • We propose a novel WSN-based approach as a competi- tive alternative of current technologies. • We designed a novel algorithm that can effectively handle emergency preemption requests. • We implemented a prototype to test the model and per- formed a theoretical analysis on the system performance. • The results show that our system is feasible with high preemption accuracy, and has multiple advantages. The following are the main advantages of the proposed sys- tem: – Cost efficiency: The main components of the WSN- EVP system cost less than comparable systems. – Reliability: The system is programmable which makes it flexible to meet the security (e.g. Authen- ticity) and the fast response requirements. – Maintainability: The system able to identify dysfunc- tional motes. – Scalability: The range of the system is extendible and can deploy multi-hop EV signal detectors. The rest of the paper is organized as follows: In Section II, review of related work is given. Section III introduces the solution approach. The WSN-EVP algorithm design is given in Section IV. The prototype implementation and results are discussed in Section V. Conclusion is presented in Section VI. II. RELATED WORK EVP systems involve several techniques that include optical- based, sound-based emitter/detector [7], and GPS-based sys- tems [10]. Each method uses a particular validity mechanism to secure intersection preemption of an approaching EV with a safe travel and minimum delay. Optical systems are based