Abstract—Vehicular Ad hoc Networks (VANETs) are recognized as an important component of the Intelligent Transportation Systems. Thanks to this emerging technology, new information will be available to design better adaptive traffic light control systems which will dramatically improve the traffic flow. In this paper, we present a novel VANET- based approach to obtain (1) the position of the last vehicle and (2) the number of vehicles, in a line of vehicles stopped at a traffic light. We also show that our algorithm to estimate the position of the last vehicle will still function even if just a few vehicles are equipped with VANET technology (low penetration rate), which is important since it will take years for all vehicles to be equipped with VANET technology. Keywords: DSRC, Adaptive Traffic Light Control Systems, VANET, V2V (Vehicle-to-Vehicle Communication), V2I (Vehicle-to-Infrastructure Communication), Vehicular Networks, Intelligent Transportation Systems. 1. Introduction Vehicular Ad hoc Network (VANET) is a promising, emerging, new technology that integrates the capabilities of wireless networks to vehicles. VANET shares some common characteristics with the general Mobile Ad hoc Network (MANET), such as the movement and self-organization of the nodes. Indeed, some researches consider VANET as a kind of MANET. However, they also have some significant differences that tend to separate them and motivate the development of new specific algorithms, especially for routing protocols [13]. MANETs can contain many nodes that are power constrained and are subject to uncontrolled moving patterns [10]. On the other hand, most of the VANET nodes do not have battery issue since their indirect source of power is the gas in the fuel tank of the vehicle, and their movements are constrained by the road and traffic pattern. In most case, the mobility of vehicles in VANET is assumed to be the car following model [21], in which cars follow one after the other in a streamlined fashion. There are two types of special electronic devices in VANET: On Board Units (OBUs) and Road Side Units (RSUs). OBUs are placed inside each vehicle and therefore are mobile. RSUs are fixed and installed near the road. Vehicle-to-Vehicle (V2V) communications take place between OBUs, while Vehicle-to-Infrastructure (V2I) communications involve OBUs and RSUs. A VANET- enabled vehicle should be able to receive and relay messages to other VANET-enabled vehicles in its neighborhood (also known as multi-hop relaying), as shown in Fig. 1 where car A is sending a message to car C through car B. B A C Fig. 1. Example of a Vehicular Ad hoc Network In the US, the Federal Communication Commission (FCC) allocated a 75 MHz of spectrum in the 5.850-5.925 GHz band for Dedicated Short Range Communication (DSRC) for the Intelligent Transportation System (ITS) [11]. The usage of VANET in the ITS is mainly focused on safety and will be extensively used for collision prevention, forward obstacle detection and avoidance [7], blind crossing, and approaching emergency vehicle warning (Blue Waves). Other important applications are traffic congestion detection, adaptive traffic Eric Gamess 1 and Imad Mahgoub 2 1 Escuela de Computación, Universidad Central de Venezuela, Los Chaguaramos, Caracas 1040, Venezuela 2 College of Engineering and Computer Science, Florida Atlantic University, Boca Raton, Florida 33431, USA A Novel VANET-Based Approach to Determine the Position of the Last Vehicle Waiting at a Traffic Light Int'l Conf. Wireless Networks | ICWN'11 | 327