## 3 Methodology and Data Collection
### Data Collection
#### 3.1.1 Road Segments  
According to ISO 14819-3:2013 [46] (managed by Traveller Information Services Association, Brussels), approximately 20,500 road segments are defined within the road network of the Czech Republic (called travel message channel (_TMC) segments_ for historical reasons) and each of them is identified using a unique _Tmcld_ text identifier. A total of 37,002 km of roads is covered out of 56,000 km of all-category roads in the Czech Republic. In this research, we thus used 66% of all roads in the Czech Republic. Certain local or purpose-built roads were excluded from the classification, as the traffic on these roads is very low.  
Real-time traffic information (see Figure 1) were available for these _TMC segments_ and they were mapped onto the road segments in OpenStreetMap (OSM) by means of TMC location tables. Furthermore, these road segments were divided into parts of length of 500 m at maximum, which we call _OSM segments_, and they were identified a by combination of _Tmcld_ and _OffsetId_ (defining order of _OSM segments_ within _TMC segments_). Geographical coordinates of the beginning and end of the segments were available for each _OSM segment_. The reason for dividing them into the maximum length of 500 m per each _OSM segment_ was to map the weather forecast data as accurately as possible. We mapped _TMC segments_ to _OSM segments_ because these maps were available free of charge and are used by a number of navigation solutions which could easily connect the prediction model designed here to their solution.  
An important factor for each _TMC segment_ is the _FreeFlowSpeed_, i.e., the passage speed under ideal weather conditions without any restrictions arising from the density of other traffic or construction restrictions. The _FreeFlowSpeed_ is restricted from exceeding the maximum speed limit arising from traffic regulations for the given road segment. For each of the segments, we can monitor how the actual measured speed deviates from the _FreeFlowSpeed_.  
For each _OSM segment_, additional information was gained from the OSM, which can affect the traffic flow in the given segment--in particular, the type of road (e.g., motorway, major road network, first class road), the actual length of the segment, the number of public transport lines using this segment, and the number of public transport stops, traffic lights, pedestrian crossings, level crossings, and driving traffic lanes. Not all of these segments had such attributes.  
Data assignment from the OSM was carried out automatically, and it must be noted that it was not always entirely accurate. For instance, it is possible for some of the _OSM segments_ comprising \(1\)_TMC segment_ not to have the identical type of road set. Despite  
Figure 1: _TMC segments_ according to _RoadType_ displayed on the map of the Czech Republic.  
this fact, OSM data helped with the further data processing and some of the inaccuracies have been already corrected. Figure 1 contains the road network on the map of the Czech Republic with colorful highlights of segments depending on their type. The displayed segments only include the road segments in the Czech Republic where traffic information was available (as a result, certain fragments are entirely separated).  
Figure 2 contains the frequency of _TMC segments_ according to their _RoadType_. We distinguished between Motorway (M), Motorway link (ML), Trunk (T), Trunk link (TL), first-third class road (1, 2, 3), their slip roads (1L, 2L, 3L), and finally, Residential (R), Service (S), Track (Tr), and Other (O).