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Table 2 List of explanatory variables, with their symbol, unit and data source

From: Safety assessment of Czech motorways and national roads

Element type Symbol Variable [unit] Data source a
Interchange conflict points AADT Annual average daily traffic [veh/day] NTC + own survey
Type Type of conflict point (merging, diverging, etc.) online maps
Signal Traffic control device (unsignalized/signalized) online maps
Channel Channelization by road marking (no/yes) online maps
Directions Number of driving directions online maps
Interchange ramps AADT Annual average daily traffic [veh/day] NTC + own survey
L Length [m] RMD
Ramp Type (on-ramp, off-ramp, etc.) online maps
Curve Horizontal curvature (straight/curved) own GIS
R Horizontal radius [m] own GIS
Sections between interchanges AADT Annual average daily traffic [veh/day] NTC
L Length [km] RMD
Access Number of accesses per kilometre RMD
Parking Number of available parking space RMD
Intersections on national/secondary roads AADT Annual average daily traffic [veh/day] NTC
Location Location in rural/urban areas online maps
Control Traffic control device (yield, stop, signals) online maps
Bypass Bypass lane (no/yes) online maps
Turn Turning lanes (no/yes) online maps
Legs Number of roundabout legs online maps
ICD Roundabout inscribed circle diameter [m] online maps
Island Roundabout central island diameter [m] online maps
Entry Average of roundabout entry angles [°] online maps
Deviation Average of roundabout deviation angles [°] online maps
Circ Width of roundabout circulatory lane [m] online maps
Apron Width of roundabout track apron [m] online maps
Sections of national/secondary roads AADT Annual average daily traffic [veh/day] NTC
L Length [km] RMD
Urban Ratio of location in urban areas own GIS
Minor Number of minor intersections per kilometre online maps
CCR Curvature change rate [gon/km] own GIS
  1. a NTC national traffic census, RMD Road and Motorway Directorate of the Czech Republic