## 4 Conclusions  
In this paper we have presented a driver assistance system that involves pre-collision actions with obstacle detection and vehicle-to-vehicle communication to alert the driver of danger situations. To this end, the controls of a vehicle were automated. The vehicle was also equipped with a laser scanner technology-based vehicle surroundings perception system and with a wireless communications module. The practical application was focused on a system that activates in the face of obstacles in the lane on a single-carriageway road, where there are two possible actions: braking or avoidance. Combining a pre-collision avoidance system with a cooperative warning represents an innovation over other already developed systems. For example, pre-collision systems can give rise to sudden manoeuvres that pose a risk to other road users. However, in the developed system the whole vehicle environment is assessed so that the best possible action can be chosen and other users warned of the risk. On the other hand, if we are dealing with systems that detect vehicles or obstacles in general, give rear-end collision warnings or warn of vehicles that are moving abnormally slowly or are stopped on the road, if the system is autonomous it only detects the obstacle but does not alert other road users who may be caught unaware of the same obstacle. However, if the detection is done by communications between vehicles all of them need to be equipped with communication systems. A similar situation arises in assistance systems for overtaking. If these are communication-based then the system needs to be widely implemented in the vehicle stock. This is not the case with the proposed system since obstacle detection is based on autonomous sensors and communications are only used to alert other drivers of the fact that the vehicle with the collision avoidance system is going to perform an evasive manoeuvre to avoid an obstacle. Finally, a system such as the one developed enables early warning alerts to be given to other road as warnings can be given after detecting the risk but before carrying out the avoidance manoeuvre. Hence, this is a basic ADAS but a good example to demonstrate the benefits of combining a standalone headway vehicle detection system with automatic actuation with a communication system to transmit an emergency signal, generating a cooperative perception system. This combination tries to take advantage of each system, considering the fact that the system should be useful for the vehicle that includes it from the beginning, independently of the market penetration, and would help others users in case they include the appropriate receivers. The proposed system applies the obstacles detection and tracking algorithms that have been previously proved and better results than previous techniques have been obtained [43]. Furthermore, apart from the detection of obstacles and their positioning on a digital map according to the knowledge of the accurate position of the vehicle with the system, accurate and detailed digital maps [37,49] are used for assessment of free areas where movement of the vehicle is safe enough. This fact improves de decisions module capabilities in relation to some previous works because information increases and the possibility of wrong maneuvering decisions diminish. The decision module for assessing overtaking maneuvers is based on theoretical models, but experimental tests have been carried out in order compare results in lane change maneuvers and adopt decisions that could be actually implemented in a real situation. Finally, the communications module is used to alert other drivers, because some automatic actins could be severe and intrinsically imply some sink to vehicles that are moving behindthe one with the system. This is a module that works independently but improves the functionality of the whole system. Obviously, communications between vehicles allow earlier detection of hazardous situations, but above cited limitations reduce their effectiveness.