## 5 Use Cases
### Accessibility Surveillance System at Stops  
The accessibility and safety of passengers of vehicles at stops and stations is an important aspect of public transit service, given that it impacts the comfort level of the service rendered, the commercial speed of the vehicles, and the circulation of remaining vehicles. If the area set up for the parking of public transit vehicles is not distinct, the bus must park outside of this area, which implies the following conditions:  
Figure 5: Details of the data communicated via the protocol. * A risk for passengers, given that they must enter the thoroughfare on occasion. * An inconvenience because they must move outside the vehicle access area, carry luggage, and accompany children or people with mobility problems. Parking outside of the parking area at stops may create access mechanisms for people with mobility problems, e.g., access ramps do not deploy, which impedes access to these travelers. * Decreased commercial speed given that the vehicle must perform complex maneuvers for parking, which enables passengers to board and disembark. * Interrupts the circulation of other vehicles, given that they must park by entering the thoroughfare, which increases the risk of accidents. The surveillance of exclusive public-transit vehicle zones (stops, stations, and bus-only lanes) in urban areas can be conducted using imaging sensor networks installed at main points in the transit network (stops, stations, and in the public right-of-way); an example is the ISTIMES system [20], which has been referenced in the section about related studies. Conversely, this solution is not possible for public transit in non-urban areas because the availability of basic resources (electricity and communications) is not always guaranteed, especially at points in the transit network in isolated rural areas. The solution proposed by the system consists of utilizing exterior cameras that are installed in vehicles as a type of mobile imaging sensor network. It is a deterrent system for drivers who park their vehicles in areas reserved for public-transit vehicles. When a bus reaches a stop, the system will activate the camera and obtain a series of images of the stop; in the case in which a vehicle is poorly parked, this video will be sent to traffic authorities with the objective of initiating a citation. The surveillance system is activated when the vehicle is traveling along its route. The required data are obtained from the data frames sent by the infrastructure using the protocol described in the previous section. These data include the vehicle identifier, driver identifier, vehicle operating status, route ID, and vehicle positioning. When the vehicle is performing route service, these data are provided by the infrastructure. Figure 5 shows the packet sent by the infrastructure to the OBC from which these data are obtained. With these data, the system runs as follows:  
1. Start of acquisition: Image acquisition is automatically activated when the vehicle is near the next stop on the route. The proximity is expressed by the distance threshold D, which is associated with each stop along the route. Proximity is obtained by calculating the distance between the current position and the geographical point of the stop; when the distance is less than D, the system activates image acquisition. Considering the limitations of measurement accuracy of a conventional GPS, the distance D must not be less than 100 m.
2. End of acquisition: Image acquisition is stopped when the vehicle is more than D from the last stop reached by the vehicle. The acquired images are recorded in a file and stored in the OBC. 3. Referencing images in space and time: To determine where and when the images were acquired, each file is referenced by geography and time (date and time) using data from vehicle positioning. 4. Transfer of image files: When a vehicle makes a scheduled operating stop in a place with Wi-Fi infrastructure (stations, main stops, or garages), the video files are transferred to the image repository of the company.