## 2 Traffic Characteristics and Weather in Slovenia
#### Traffic Flow Speed Analysis  
In order to further analyse the results and evaluate the measures taken to control HGVs, we also determined the empirical speed distribution functions of light and heavy vehicles at mentioned test sites near Ljubljana. We considered the vehicle categorisation of the current AHTMS, which groups vehicles into light and heavy vehicles [36]. At the same time, in the years before the COVID-19 pandemic, there were no special administrative limits or overtaking bans for HGVs. Figure 2(a) shows the results of the speed analysis for the example of test site 0178 for lane 2 for passenger cars (_pc_), and Figure 2(b) for lane 1. Similar results are shown in Figure 2(c),d for lanes 1 and 2 for heavy vehicles (_lv_).  
For test site 0865 in the Vipava Valley, we also investigated the influence of wind on the speed \(V\) of all vehicles (Figure 4). We determined four empirical distribution functions of speed \(V\) as a function of four types of AHTMS measures with respect to wind strength for traffic lane \(i\). Wind strength was expressed not by the magnitude of some other statistical characteristic value (e.g., the maximum speed of wind gusts), but by the traffic management measure \(Z_{i}\) for a specific vehicle category [36]. \(Z_{0}\) means that the wind does not require any special traffic management measures. An example of speed analysis for test point 0865 is shown in Figure 4. Nevertheless, in brackets, we still present the informative values of maximum wind gust speeds for individual bans or traffic management measures [44]:  
* \(Z_{1}\): exclusion for camper vans, refrigerator vehicles, and sheeted vehicles with the MAM of 8 t (wind from 80 km/h to 99 km/h);
* \(Z_{2}\): exclusion for camper vans, all sheeted vehicles, and refrigerator vehicles (wind from 100 km/h to 129 km/h);  
Figure 2: Example of scatter graph of time mean speed vs. traffic flow rate on the carriageway near Ljubljana in different traffic lanes: (**a**) lane 2—left (overtaking) lane; (**b**) lane 1—right lane.  
* \(Z_{3}\): exclusion for camper vans, all \(Z_{2}\) level vehicles, and buses (wind from 130 km/h to 149 km/h);
* \(Z_{4}\): ban for all vehicles--road closure (wind over 150 km/h).  
Figure 4: Empirical speed distribution functions with different traffic management measures in the case of wind at test point 0865: **(a)** lane 2—left (overtaking) lane; **(b)** lane 1—right lane.  
Figure 3: Empirical speed distribution functions for different weather conditions at test site 0178: **(a)** passenger cars in lane 2; **(b)** passenger cars in lane 1; **(c)** heavy vehicles in lane 2; **(d)** heavy vehicles in lane 1.  
In the case of measure \(Z_{4}\), the highway is closed for all vehicles, which means that only light passenger cars that leave the traffic network and are not yet familiar with traffic control measures are subject to speed measurements. If wind gust speeds exceed a certain level with a simultaneous increase in wind strength and vice versa, highway or expressway traffic is regulated in accordance with the decision of the supervisory group of the traffic operators. If a negative trend occurs, the ban is lifted. Each such turn takes up to 2 h.  
In the case of extreme winds, heavy traffic is excluded or the road is closed; hence, this generally does not affect the highway capacity utilisation. Thus, we did not consider the influence of wind on a possible measure of the truck overtaking ban.