## 2 Traffic Characteristics and Weather in Slovenia  
Slovenia is a very geographically diverse country, located in Central Europe, part of the EU and part of the Schengen area [39]. In addition to the high share of transit freight traffic, during the tourist season, there is a large flow rate of passenger cars from Central Europe towards the Adriatic and vice versa, especially in recent times following changes in travel habits due to the world facing the COVID-19 pandemic [40]. The highway network runs both through the mountainous region, where the roadway is most exposed to snowfall and ice, and through the Mediterranean belt, where a strong wind called Burja has the strongest influence. Due to its geographical diversity, it is difficult to accurately predict weather conditions in Slovenia. Different weather phenomena dictate adapted driving, but problems most often arise in the traffic control of trucks and buses in transit. Traffic safety is particularly at risk on road sections where weather conditions change very rapidly or where combined adverse weather phenomena occur frequently (e.g., big storms with snow drifts, heavy precipitation with poor visibility, and fog). Traffic control operators generally advise drivers to drive more carefully. At the moment, for a greater level of safety in bad weather conditions, the following traffic management measures are implemented: restrictions, detours and exclusion of trucks and buses, restrictions of sudden changes of direction when changing lanes or restrictions on overtaking, speed control, and information on alternative routes. Most highways are four-lane with an AADT of up to 90,000 vehicles/day, of which up to 9000 are heavy vehicles/day [41]; however, on certain highways, traffic volumes are often 2-3 times higher during peak seasons, and the same is true for HGVs on peak days such as Mondays and Thursdays. The traffic manager, the concessionaire The Motorway Company in the Republic of Slovenia (Slovenian: Druzba za avtoceste v Republiki Sloveniji, DARS), has set up an AHTMS with a network of traffic sensors providing aggregated traffic data in traffic lanes with a measurement interval of \(T=1\) min and \(T=5\) min. Similarly, data on road weather conditions are available from the Road Weather Information System (RWIS). Environmental weather data from the RWIS were recorded in the time interval of \(T=5\) min. We focused on test site 0178 with a high traffic flow density near Ljubljana (N46.035, E14.452) and test site 0865 in the Vipava Valley (N45.855, E13.945), where strong winds often occur. To investigate the characteristics of traffic flow, we joined traffic flow and environmental records into a single database and presented them in time intervals of \(T=5\) min as a part of a separate survey [19], i.e., before the COVID-19 pandemic. We should point out that the pandemic situation in the year 2020 significantly changed traffic flow patterns in Slovenia. Labels of groups of time-related environmental data were assigned to the selected characteristics of traffic flow, i.e., affixes to labels of \(d\) for dry road, no precipitation, and good visibility, _w1_, _w2_, and _w3_ for wet road and rain at the same time (of three levels), _lv_ for low visibility, but no precipitation, and _s for snowfall and winter road conditions. Group \(d\) included data based on measurements of ideal or prevailing weather conditions, defined according to [42]. Traffic flow characteristics were classified into groups _w1_, _w2_, and _w3_ according to the rainfall intensity and road wetness [36]. In group _lv_, we classified traffic characteristics at the time when visibility was lower than 250 m, regardless of meteorological conditions on the roadway. Group \(s\) was defined on the basis of data from the RWS, which uses a specific algorithm to classify precipitation and detect light, moderate, and heavy snowfall and determines conditions on the roadway surface using built-in road surface sensors [25].