## 3 Related Research Studies  
Both transportation companies and regulatory authorities are interested in acquiring the information necessary to verify that public transportation services are provided according to plan to optimize their operations and improve the quality of the service they provide. According to [PERSON] [3], this information is obtained from four different sources of data: surveys of travelers, rate of use records obtained from the vehicles, automatic passenger counting (APC) systems and automatic vehicle location (AVL) systems. Different studies related to each of these techniques for obtaining data are described next. Surveys of passengers are a tool that is frequently used by companies and regulatory agencies to collect information about the use, preferences and assessments of public transportation users. While obtaining information in this manner is expensive, regulatory agencies regularly resort to surveys because they are very useful and precise [4]. According to [PERSON] _et al._[5], the use of rate-of-use records obtained from vehicles has two associated problems: first, their high cost because they require human intervention, which leads to a reduced amount of data being collected as a result, and second, the possibility of errors in the data collected or in their transcription. In general, onboard devices that provide these data are driver consoles and reading/writing terminals of magnetic or intelligent cards. APC systems are based on the use of different types of sensors, such as infrared light [6] and acoustic [7], optical [8] and even Bluetooth technology [9] to detect the presence of travelers in the vehicle. These sensors are usually installed in the entry and exit points of the vehicle. These systems are associated with the following problems: the information that can be obtained from them is limited, e.g., they do not provide data on the position of the vehicle and can contain errors due to incorrect operation of the hardware devices or an erroneous assessment of the presence of a passenger in the vehicle. In addition, depending on the technology being used, these systems require systematic maintenance activities such as recalibration of the sensors. AVL systems are based on the use of different technologies, such as odometers [10], RFID [11] and GPS. These technologies can detect the presence of the vehicle at a specific point, for example, infrared markers, or locate the position of a vehicle at any moment in time, for example, GPS. These systems also have problems: first, they provide no data on the occupation of the vehicle, and second, systems that continually provide the position of the vehicle have a lack of precision. For example, a standard GPS can produce positions with an error radius of 100 m, and different techniques are required to reduce errors to 10 m. Two examples of these techniques are differential GPS, which requires constant communication with a remote place to receive the position corrections, and the technique proposed by [PERSON] [12] for urban areas in which satellite signals are low quality that is based on image processing. Another problem associated with these systems is that for the information to be useful, the data must be recorded in a continuous manner. The previous paragraphs cited research works that describe different techniques and technologies used to obtain useful data to aid in the control and improvement of public transportation for travelers. The following paragraphs will describe the studies that address what types of data are needed and in what quantity such that they can be useful for different agencies and companies, in other words, for them to be interoperable. Planning of a public road transportation system for travelers involves determining in an optimal manner, if possible, a plan for routes, frequencies, schedules, personnel and fleet allocations.