Opportunistic System for Collaborative Traffic Monitoring Using Existing IEEE 802.11 Networks Jos´ e Geraldo Ribeiro J´ unior *† , Miguel Elias M. Campista * , and Lu´ ıs Henrique M. K. Costa * * Grupo de Teleinform´ atica e Automac ¸˜ ao, UFRJ - COPPE/PEE - DEL/Poli, Rio de Janeiro – RJ – Brazil Email: {jgrjunior, miguel, luish}@gta.ufrj.br † CEFET-MG - Campus III - Leopoldina - MG - Brazil Email: {jgrjunior}@leopoldina.cefetmg.br Abstract—Traffic monitoring and control is getting more and more important as the number of vehicles and traffic jams steadily grow. Nevertheless, traffic control is still predominantly done by visual means using strategically placed video cam- eras. To be more effective, proposals to improve the traffic conditions should consider automated monitoring systems. This work proposes an opportunistic system for collaborative traffic monitoring using available IEEE 802.11 networks. Based on the information received by 802.11 beacon frames, vehicles provide the data needed by a central entity to handle and disseminate information about traffic conditions on urban roads, exploiting readily available network resources. Experiments performed with data from a real public wireless network, in Rio de Janeiro, demonstrate the possibility of obtaining traffic conditions with our proposed traffic monitoring method. The system results are close to GPS traces. Moreover, the proposed system facilitates large-scale adoption since it does not require specific hardware. I. I NTRODUCTION At a time when the world is about to reach the mark of almost two billion vehicles in circulation [1], inevitably over- loading roads, traffic monitoring and control have become of utmost importance. Big cities, such as Rio de Janeiro, Brazil, have to deal daily with traffic jams as a consequence of car crashes, road repairs or even sudden speed reductions. Another direct consequence of traffic jams is the increased emission of carbon dioxide (CO 2 ) and other pollutants in the atmosphere. According to INEA (Rio de Janeiro’s Environment Institute), vehicles account for 77% of the total pollutants emitted into the atmosphere, 25% to 30% in a single large avenue, Brazil Avenue [2], an important 58 km central road in Rio de Janeiro city. Thus, taking preventive actions is a priority. Proposals to reduce traffic problems require efficient and automated monitoring systems. Nevertheless, the strategy most used in Brazil is still the old-fashioned manually operated video cameras, where all the traffic control is visually done. Some proposals use sensors in cars or along the road [3]–[5], or combine the use of GPS (Global Positioning System) with either GPRS (General Packet Radio Service) [6], or 3G [7]– [9] or even with IEEE 802.11 [7], [10]–[13]. Whereas sensors are expensive because they are not yet produced in large scale, the use of GPS or 3G results in battery consumption of portable devices three times larger than IEEE 802.11 [10], [14]. Another problem of 3G technology, besides the cost to the final user, is the deteriorating quality of service because of the increasing demand, which is making mobile phone companies limit users’ maximum rate [15]. The use of GPRS has the advantage of wider coverage because it uses the cellular network, but the upload rate is very low compared with IEEE 802.11 [14]. This paper proposes an opportunistic system for collabo- rative traffic monitoring using already installed IEEE 802.11 networks. The key idea is based on the popularity of smart- phones and on the growth of the number of projects that offer Internet access to wide urban areas using IEEE 802.11. Solely using information derived from beacons of available IEEE 802.11 networks, we infer the location, direction, and speed of vehicles, with no need for new investments or modifications on existing protocols. Client nodes are vital in the process because they are in charge of receiving and filtering data. Afterwards, they send the obtained information to a central unit, which proccesses the received data before sending back consolidated information to users. The user only requires a machine with an IEEE 802.11 interface card to take advantage of the network service. We evaluate our proposal by collecting and analyzing data on a real scenario. Our experimental results show that it is possible to monitor the traffic conditions based in the received power signal. We evaluated the accuracy of our results compared with control data obtained by GPS. Our results show that the obtained values are very similar and even with a received signal with power as low as -60 dBm there is a discrepancy of less than 10 meters. A key advantage of our proposal is its capacity to be incrementally deployable since it is not necessary to have 100% of vehicles sending information. The remainder of this paper is organized as follows: Sec- tion II details our vehicle monitoring system. Section III analyzes experimental results while Section IV concludes the paper and presents topics for future investigation. II. PROPOSED METHOD Traffic monitoring systems do not require a high level of accuracy to find vehicle location on roads [16]. Errors are minimized by predictability of client node movement. Exper- iments presented in Section III show that a signal received 7294