**4.1.3 Slippery road detection**

456 Wireless Communications and Networks – Recent Advances

anonymously share relevant information, including their position, speed and direction. This way each vehicle monitors the intentions of other drivers and the location and behavior of all vehicles in the neighborhood. When a vehicle detects a critical situation, the system warns the driver with a visual, audible and/or haptic manner. Thus, the driver has enough

In time critical situations, immediate intervention to avoid a collision is feasible with the use of communication. This would not be possible in case only onboard sensors were used because of the delay in detecting and classifying objects and analyzing the ongoing situation. The co-operative approach also has great influence on the classification of objects. If vehicles are equipped with wireless communication they can directly exchange

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

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.

time to intervene and avoid a collision.

**4.1.2 Intersection safety** 

that limit the visibility of the driver.

Fig. 5. Intersection safety application.

information about their type (e.g. truck, car, motorbike).

This application informs the driver about the status of a road segment where there is a possible risk. The risk is primarily related to a slippery road surface that may be due to adverse weather conditions (e.g. ice, rain) or to any extraordinary event (e.g. an oil leak of the vehicle ahead). The detection of the slippery road segment can be carried out by a vehicle either directly by specific sensors or indirectly by activation of the ABS or ESP system. Even though this information, about the dangerousness of the road, is transmitted to the driver directly, it may be too late to take action because it is highly likely that the vehicle has slipped already since the ESP or ABS has been activated. A slippery road detection application is depicted in Figure 6.

As it is obvious, this application has almost no interest without the use of wireless communication. By taking advantage of wireless communication the vehicular network can share information related to hazardous road segments such as slippery roads. For example, a vehicle that its ESP system is activated associates this data with its current location and notifies other nearby vehicles and possibly a RSU if it is in communication range. The neighboring vehicles receiving such information shall promptly inform the drivers about the potential risk, while retransmitting this information to other nearby vehicles (multi-hop communication). As an alternative, a RSU can be equipped with some special sensors which can detect the hazardous road conditions and inform the drivers approaching this area.

Fig. 6. Slippery road detection application.

As a conclusion, there is an apparent advantage in using wireless communication to broadcast information about the road conditions to the approaching drivers who will then have sufficient time to react. With this co-operative approach the RSU has the ability to transmit road condition information to the traffic management center which then can be analyzed and checked for accuracy and quality and transmitted to other vehicles that drive on this road segment.
