# Semantic Traffic Sensor Data:
## 2 Related Work
### Sharing Smart City Traffic Data  
Several works have been published to define how to structure and share data produced in a smart city [14]. Smart urban traffic ecosystems are identified in [15] as an example of a \"big service\", \"evolved from the collection of collaborating, interrelated services for handling and dealing with big data\". By collecting suitable sensor data and defining appropriate data exploitation strategies, it is possible to empower both citizens and decision-makers to improve our quality of life. However, for this dream to come true, the development of suitable data management strategies that can provide citizens and administrations with the information they need is a key issue. Thus, for example, according to [16], informational interventions are vital to encourage changes in attitudes and perceptions of people. Along the same lines, the work presented in [17] emphasizes that \"open data can impact positively on citizens in particular and society in general\".  
Traffic data can help in detecting traffic congestion, providing traffic flow prediction, and identifying traffic accidents. For this reason, several projects have published traffic information as open data. To lower the barrier for open data consumers to reuse traffic information, an Open Traffic Lights ontology has been proposed in [18]. That paper also reports a specification to publish historical and live data with Linked Data Fragments and a method to preserve the published data in the long-term. In [19], for measuring the urban road congestion degree, that is one of the major issues in most metropolises, the estimation of a Traffic Congestion Index (TCI) of every road segment at every time slot has been proposed. As a final example, an open traffic data platform has been presented in [20] and used as a sensor data provider for different management applications.  
The increased interest in smart city data sharing for the public interest can be assessed by the number of datasets shared on the open data portals. When we searched in the European Data Portal for \"traffic\", we obtained 8949 datasets (search done on 5 August 2020: [[https://www.europeandataportal.eu/data/datasets?locale=en&query=traffic&page=1](https://www.europeandataportal.eu/data/datasets?locale=en&query=traffic&page=1)]([https://www.europeandataportal.eu/data/datasets?locale=en&query=traffic&page=1](https://www.europeandataportal.eu/data/datasets?locale=en&query=traffic&page=1))). Even if transport data only cover a 2.25% of the total datasets (see the European Data Portal statistics per category at [[https://www.europeandataportal.eu/catalogue-statistics/CurrentState](https://www.europeandataportal.eu/catalogue-statistics/CurrentState)]([https://www.europeandataportal.eu/catalogue-statistics/CurrentState](https://www.europeandataportal.eu/catalogue-statistics/CurrentState))), a positive trend can be observed. Mainly, traffic open data are statistics that show the number of registered cars in different countries, and they are usually provided in the form of high-level vehicle fleet data in a city. On the other hand, data concerning the average daily traffic volumes on different roads and the specific traffic volume on different days and at different hours on specific road segments are not always shared with citizens. We argue that having these data would be remarkably useful, as their exploitation could enable politicians of our cities to make more informed decisions, and the public could also be better informed about the traffic situation and use real data to promote health and environmental protection. The publication of the data as Linked Data enables a suitable and interoperable sharing of data that can facilitate the development of applications and services for smart cities [21; 22].