## 4 Discussion  
The analysis of the recorded dwell time values showed that the average stop dwell time for all three tram vehicle types stopping at the three tram stops under observation was 13.9 s. Compared to the recommendations of the HBS and HCM, i.e., a mean stop dwell time of 25 s, this average dwell time was significantly lower. It can be argued that this difference was a direct consequence of the COVID-19 restrictions in PT where the occupancy of tram vehicles was limited to 40% of the maximum value. However, the recorded passenger volumes for which dwell time value was obtained varied from less than 10 to more than 200 passengers per hour, as expected on platforms located near the city center. Unlike the HBS, the HCM states that stop dwell time can be reduced to 20 s or even 15 s, which was significantly closer to the value obtained in the investigation presented in this paper. The analysis of the influence of tram type on stops dwell time indicates that for a small number of passengers boarding and alighting tram vehicles (a total of less than 20 passengers), dwell time was more affected by the tram door opening mechanism and opening/closing time and less by door number, width, and floor height. Of all tram vehicles, the smallest and the oldest tram, TMK301, which had an elevated floor and four narrow doors (divided into two accordion-shaped parts equipped with a primitive door mechanism opening quickly by folding), achieved the shortest average dwell time of 13.0 s. The newer tram, TMK2100, which had an elevated floor and five double panel sliding doors, achieved an average dwell time of 15.6 s. On the other hand, the largest, newest, and most modern tram type, TMK2200, which had a low floor and six wide double-panel doors, achieved the longest average dwell time of 16.3 s. These findings corresponded well with the results from the investigations regarding the influence of door type and floor height  
Figure 14: Dependence of dwell time on the type of passenger flow on the busiest tram doors. Figure 13: Distribution of passengers alighting and boarding tram vehicles. on rail PT stop dwell time. Namely, according to [27], steps do not prolong the process of boarding. According to [28], door width was not the critical stop dwell time factor per se because of physical constraints and typical passenger behaviors, i.e., increased door width does not significantly improve the rate of boarding or alighting flow, but it does have the benefit of enabling these to occur simultaneously for a few seconds. According to [29], the average additional time per stop required for the larger doors to open and close was 1-2 s. The longer additional time obtained in this research (2-3 s) can be explained by the fact that, unlike TMK301, newer TMK2100 and TMK2200 vehicles have built-in safety systems that prevent the door from opening until the vehicle is completely still and they cannot start until the door is completely closed. It was observed that the influence of the door mechanism on dwell time weakens as the passenger volumes become higher and that the number of doors per vehicle gains its importance. The analysis showed that with regard to stops and vehicles, there was no uniformity in the alighting passenger distribution through specific doors. This can be explained by the fact that passengers do not change their position inside the vehicle due to the short inter-station distances. Namely, passengers prefer to travel in the same part of the vehicle and alight the vehicle through the same door they have boarded independently of the occupancy and distribution of passengers inside the vehicle. The analysis of the boarding passenger distribution along platforms showed that, on average, 54% of passengers board through the door closest to the shelter. Therefore, it is safe to assume that waiting passengers on less-occupied platforms are grouped in the shelter zone. Another distinct waiting location is by the station pole.