**4.1.2 Intersection safety**

A significant number of accidents in urban areas occur at intersections. The reasons for this are the significant burden of the driver from the complex situations that can occur at intersections due to many vehicles that are flooding them from different directions, the variety of road users (cars, trucks, pedestrians, cyclists etc.) as well as buildings and walls that limit the visibility of the driver.

In order for an accident or a dangerous situation to occur at an intersection it is supposed that there should be a violation of traffic rules such as traffic light or "STOP" sign violation. But intersections are complex road environments and accidents are likely to occur even if the rules are obeyed (e.g. abrupt braking while the traffic light turns from green to red). A simplified example of an intersection safety application is shown in Figure 5.

Fig. 5. Intersection safety application.

The benefits from the exploitation of wireless communication for safety reasons at intersections are significant. First of all, the traffic lights and other traffic signs can emit their status, together with information concerning the instant that this status is going to change (e.g. traffic light that turns from red to green), to the interested drivers informing them about the real ongoing situation at the intersection. In addition, vehicles can emit their position and dynamic state (speed, acceleration, steering angle) and thus to inform other drivers at the intersection about their presence. Otherwise it would be impossible for other drivers to be aware of their presence because of the occlusion of the surrounding buildings, walls and other obstacles. Finally, some sensors, such as laser scanners, could be installed at critical points at an intersection to detect pedestrians and cyclists (vulnerable road users) and inform the drivers for their presence through wireless communication.
