Taking Advantage of V2V Communications for Traffic Management Alessandro Bazzi and Barbara M. Masini Abstract—Real time information to vehicular users is propos- ing new challenging questions to which wireless systems design- ers are called to answer. Nowadays many vehicles are already equipped with devices able to connect to cellular networks, and to transmit and receive in real time traffic information through vehicle-to-infrastructure (V2I) communication. Focusing on the uplink transmission of real time measurements, this is leading to high costs in terms of network load and billing. In this work we discuss the opportunity to take advantage of vehicle-to- vehicle (V2V) in addition to V2I communications to reduce the amount of data to be transmitted from vehicles to a remote control center, and thus also to reduce the resulting costs for transmissions over the cellular networks. Having in mind to allow a first understanding of the achievable advantages, we propose a simple mathematical model through which we discuss how many vehicles are necessary to guarantee an useful V2V communication and which are the advantages in terms of network load and, consequently, costs reductions for the V2I network. Index Terms—Vehicle-to-vehicle (V2V), vehicle-to- infrastructure (V2I), analytical model, traffic related services. I. I NTRODUCTION In the last years an increasing number of vehicles trav- elling in all Countries are being equipped with devices that make them act as sensors collecting and transmitting information about themselves and their surroundings. These devices include a global positioning system (GPS) receiver, a cellular technology radio interface, and eventually other sensors. Various applications that target transport efficiency could make use of the vast information collected by vehicles: safety, traffic management, pollution monitoring, tourist in- formation, etc [1]–[3]. In Italy, for instance, over one million vehicles are equipped with on board units (OBUs) frequently collecting position and speed measurements [4]. When a significant number of measurements is collected or when a given time out is reached, OBUs transmit their data to a remote control center through the general packet radio service (GPRS) cellular technology, as represented in Fig. 1(a). The control center receives and stores the data, and is then able to process the traffic information in order to update This work was supported by the Italian project PEGASUS financed by the Ministry for the Economic Development. A. Bazzi and B. M. Masini are with IEIIT-CNR and Univer- sity of Bologna, Italy. Email: alessandro.bazzi@unibo.it, barbara.masini@unibo.it in real time dedicated web sites or to interact with particular on board devices for a smart navigation service. The increase in number of the OBUs imply higher costs due to an higher use of the mobile network. At the same time, however, increasing the number of performed mea- surements means a higher probability that the same roads are monitored with a certain redundancy. If OBUs were able to communicate to each other, measurements performed at the same time over the same road could be merged before transmission over the network, thus reducing the overall cost of the service. Whereas in [5]–[7] the impact of this real time infomobility service is investigated in terms of cellular systems capacity and users’ satisfaction, at the authors’ best knowledge still no papers are evaluating the possibility of exploiting additional communication networks to share and aggregate traffic information with the aim to reduce the cellular network load. It must also be remarked that, envisioning the presence of V2V communication, is absolutely in line with the trends in this field. V2V communication is, in fact, gaining an increas- ing interest, thanks to the inexpensive wireless connections, and to the easy installation on vehicles with few tweaks. Several standardization processes and research works are currently carried out [8], [9], giving particular attention to the wireless access in vehicular environments (WAVE) [10], based on IEEE 802.11p [11]. Decentralized ad-hoc communications among vehicles open new challenges due to high vehicle speeds and highly dynamic operating envi- ronments, thus including new expectations for high packet delivery rates and low packet latency. Many research works are in fact trying to understand the performance of V2V communication, also proposing new solutions for standard enhancements [12]–[16]. In particular, in [17] the delays and the packet delivery ratio in WAVE/IEEE 802.11p vehicular networks are evaluated by simulation for the vehicle-to- roadside link, and considering vehicles to aggregate the report received from neighbors before forwarding them. In this paper, we assume the OBUs equipped with both V2I (i.e., cellular) and V2V communication technologies, and we investigate the advantages achievable by sharing and aggregating the collected traffic information through the exploitation of a V2V communication; the scenario is shown in Fig. 1(b), where only one vehicle per road segment is in charge of collecting all the other vehicles information and