# Big Data for Traffic Estimation and Prediction: A Survey of Data and Tools
## 2 Data-Driven Traffic Estimation and Prediction  
In this section, we summarize the different types of data that can be used for traffic estimation and prediction. We also contribute an up-to-date collection of available open datasets for each data type as well as new GPS trajectory data for further studies. There are different ways of categorizing traffic big data. For example, traffic big data were previously divided into supervised and unsupervised types, in which supervised data are direct sources of traffic information, e.g., loop detectors and GPS traces, while unsupervised data are indirect sources that can be used to infer traffic information, e.g., call detail records and cell phone position data. In this study, we further divide traffic big data into more types based on data sources.  
Open data policies in different countries vary greatly. Taking the U.S. government as an example, transportation related open data can be found from the National Transit Database (NTD) ([[https://www.transit.dot.gov/ntd/ntd-data](https://www.transit.dot.gov/ntd/ntd-data)]([https://www.transit.dot.gov/ntd/ntd-data](https://www.transit.dot.gov/ntd/ntd-data))), Federal Highway Administration (FHWA) (For example, Urban Congestion Reports [[https://ops.fhwa.dot.gov/perf_measurement/ucr/](https://ops.fhwa.dot.gov/perf_measurement/ucr/)]([https://ops.fhwa.dot.gov/perf_measurement/ucr/](https://ops.fhwa.dot.gov/perf_measurement/ucr/))), Bureau of Economic Analysis (BEA) ([[https://www.bea.gov/data/](https://www.bea.gov/data/)]([https://www.bea.gov/data/](https://www.bea.gov/data/))), and American Community Survey (ACS) ([[https://www.census.gov/programs-surveys/acs/data.html](https://www.census.gov/programs-surveys/acs/data.html)]([https://www.census.gov/programs-surveys/acs/data.html](https://www.census.gov/programs-surveys/acs/data.html))).  
The Next Generation Simulation (NGSIM) ([[https://ops.fhwa.dot.gov/trafficanalysistools/ngsim.htm](https://ops.fhwa.dot.gov/trafficanalysistools/ngsim.htm)]([https://ops.fhwa.dot.gov/trafficanalysistools/ngsim.htm](https://ops.fhwa.dot.gov/trafficanalysistools/ngsim.htm))) is the most widely used open-source vehicle trajectory dataset for traffic flow studies [18]. In this study, we mainly focus on open datasets in academia. More data collections can be found online, which may be maintained by individuals and research institutes, e.g., mobility datasets ([[https://privamov.github.io/accio/docs/datasets.html](https://privamov.github.io/accio/docs/datasets.html)]([https://privamov.github.io/accio/docs/datasets.html](https://privamov.github.io/accio/docs/datasets.html))), open traffic collection ([[https://github.com/graphhopper/open-traffic-collection/](https://github.com/graphhopper/open-traffic-collection/)]([https://github.com/graphhopper/open-traffic-collection/](https://github.com/graphhopper/open-traffic-collection/))), and Beijing City Lab ([[https://www.beijingcitylab.com/data-released-1/](https://www.beijingcitylab.com/data-released-1/)]([https://www.beijingcitylab.com/data-released-1/](https://www.beijingcitylab.com/data-released-1/))).