# Smart Disaster Response in Vehicular Tunnels: Technologies for Search and Rescue Applications
## 3 Proposed Disaster Response Systems for Tunnel Accidents
### Radar Sensor for Vehicle Detection  
Recently, many intelligent transportation system (ITS) systems have been studied to monitor the flow of vehicles on the road and for the detection of dangerous situations through radar. In particular, since radar uses radio wave transmission and reception based on the Doppler effect, it has the advantage that it can perform robust and accurate position tracking in extreme conditions, such as poor illumination, smoke, snow, and rain, in comparison with existing cameras or optical sensors. In a typical conventional positioning method, a global positioning system (GPS) sensor provides the position of a vehicle or an object in real time; however, it is impossible to receive a GPS signal in a closed space, such as a tunnel. Of course, radar signals are also very distorted due to diffuse reflection, signal fading, and the ghost effect [39] in a tunnel. However, in the proposed system, a signal filtering [13] process is introduced to enable real-time vehicle tracking in a tunnel. Vehicle accident detection using a radar sensor can be performed by checking whether the vehicle is moving at excessive speed or has performed an emergency stop. In addition, information regarding lane departure using the identification, speed, direction, and coordinates of the running vehicle can be obtained in real time. For example, if a vehicle suddenly stops in a tunnel, the radar suspects an accident first. This is because the tunnel is basically an area where parking is prohibited. However, detection of flame and smoke after the vehicle has stopped can be done by camera-based image analysis. Figure 7 shows the installation of a radar in a tunnel to monitor the driving of vehicles and to display the acquired coordinates and the accident status to the control system. In Figure 7a, the leading vehicle (ID 5) of the two moving vehicles has stopped 90 m into the tunnel, and the following vehicle (ID 9) has stopped. The exact x and y coordinate values are shown in Figure 7c. The x coordinate is the distance the vehicle travels from the entrance, and the y coordinate is the horizontal distance away from the centerline of the tunnel. The radar sensor of the developed system has an accuracy of 0.25 m, and it can track up to 64 vehicles at the same time. The maximum detection distance per vehicle is about 250 m. Therefore, if two or three radars are installed in the tunnels at regular intervals, accurate vehicle position tracking and accident detection for all dangerous sections are possible. In addition, temperature, smoke, flame, humidity, and motion sensor measurements obtained by the previously mentioned fire sensor can be confirmed through the environmental information menu in the server. For multiple radar operations, we proposed a client/server based system architecture as shown in Figure 8. Each radar device encodes its acquired information and transmits it as a packet, and the server system decodes it to display the moving vehicle throughout the tunnel and confirms whether or not an accident has occurred.  
Figure 7: Vehicle Detection via Radar: (**a**) Stopped Vehicles (**b**) Radar Sensor (**c**) Detection System.