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The UN Economic Commission's Statistics of Road Traffic Accidents report of 2011 shows that every year, about 150 000 human beings lose their lives on the roads of the western world. Although it is a common belief that this figure could shrink with the use of new sensor and communication technologies, unfortunately, none such systems have hit the road to date. Ideally, if such technologies were put into place, vehicles could be part of a vehicular ad hoc network (VANET) capable of spreading relevant information about dangerous events (e.g., car accidents) to all approaching drivers. However, all this is mainly supported by simulation studies, as no practical results have been published to date, revealing the effective performances of such systems at work. In this paper, we fill this gap, presenting a detailed description of the greatest experiments (a few thousand throughout the streets of Los Angeles), to date, ever performed with an accident warning system specifically devised for highway scenarios. In particular, among all the possible candidate schemes, we ran a few thousand experiments with the accident warning system algorithm that was proven to be optimal in terms of bandwidth usage and covered distance in realistic scenarios. Our experiments confirm what has been observed before in theory and simulation, i.e., the use of such a system can reduce, by as much as 40%, the amount of vehicles involved in highway pileups. Index Terms-Design for experiments, prototypes, vehicle safety, vehicular ad hoc network (VANET) testbed, vehicular and wireless technologies. I. INTRODUCTION T HE SOCIETAL costs of car accidents in Europe, in year 2009, amounted to $160 billion according to the Harmonised European Approaches for Transport Costing project commissioned by the European Union (EU) [1]. Such value only partially captures the plethora of problems that have their origin in such type of events, as it is rather difficult to quantify, for example, the costs that are imputable to the emotional distress symptoms or to the increased pollution levels that usually follow any motor vehicle accident. Continuing with a policy that recognizes the negative impact that car accidents have on society, in July 2011, the Transport Manuscript

We present a novel protocol for fast multi-hop message propagation in the scenario of ad hoc vehicular networks (VANET). Our approach has been designed to gain optimal performance in scenarios that are very likely, but not common in literature. FROV faces asymmetric communications and varying transmission ranges. In this scenario it is able to broadcast any message with the minimal number of hops. Moreover, our proposal is scalable with respect to the number of participating vehicles, and tolerates vehicles that leave or join the platoon. At the current state of development, our protocol is optimal in the case of unidimensional roads and we are studying its extension to a web of urban roads. This paper presents the preliminary results of simulations carried out to verify the feasibility of our proposal.

The ever-increasing processing power that can today support large scale and detailed simulations increased the depth of the research carried out on protocols and apps developed for single hop and multi-hop Vehicular Ad Hoc Network (VANET) environments. It is now possible, for example, to verify the effectiveness of peer-to-peer one-hop file exchange protocols between vehicles, while taking into account the effects that buildings have on point-to-point transmissions at street intersections, or also verify how a high density of vehicles can impact the transfer of multimedia information through multiple hops between passengers involved into an online game. However, what has not been possible so far, for the obvious reason that no highly dense VANETs in reality exists, is to effectively test any type of application or communication protocol in a real setting, especially for the scenarios concerned with multi-hop communications. But this may change, with the introduction of a creative approach to VANET research: we will here describe how it is possible to experiment with applications and protocols in scenarios that are close to reality, by simply using a few real vehicle resources. As an example of how this can be done, we will provide preliminary results from a set of experiments on a vehicular highway accident warning system, results that would have not been observable in reality without the adoption of our creative methodology.