# Determining Factors Influencing Operating Speeds on Road Tangents
## 2 Methodology
### Data Collection
#### 4.2.2 Speed Measurement--Dual-carriageway Road Tangents  
Speed data for dual-carriageway road tangents were measured based on video recordings captured using an unmanned aerial vehicle (UAV)--the MAVIC 2 PRO drone (Figure 6). This drone is specifically equipped with GPS/GLOAASS satellite positioning systems and advanced sensor systems for intelligent navigation, detection, and avoidance of stationary and moving obstacles during flight. It is also fitted with a fully stabilized video camera capable of recording an exceptionally high-quality 4K Quad HD video with a resolution of 3840 \(\times\) 2160 pixels at a frame rate of up to 30 frames per second, as well as capturing photographs with a resolution of 12 megapixels. To ensure an unobstructed flight of the unmanned aerial vehicle during traffic flow recording and to maintain a high level of aerial video quality, the recording days were selected based on weather forecasts predicting favorable conditions at the selected locations. These included days with moderate temperatures, low cloud cover, and no precipitation, wind, or fog, ensuring good visibility. Prior to conducting the field research, data on the current road conditions were collected to avoid issues such as temporary road closures or traffic diversions caused by roadworks, accidents, or other incidents. The distance for speed measurements was defined along a road tangent approximately 100 m in length. Only vehicles traveling under free-flow traffic conditions were considered, ensuring that the recorded speeds were not influenced by interactions with other vehicles. Given these conditions, it is reasonable to assume that vehicle speeds remained stable over the observed segment, with no significant acceleration or deceleration occurring within this short distance. Consequently, the measured speeds can be considered representative of the constant speed travel under natural driving conditions. It should also be emphasized that the methodology used for determining vehicle speeds from aerial video footage (drone) was previously validated at a separate test location on the Zagreb bypass (dual-carriageway road--motorway). At this location, a radar speed measurement device was installed in parallel with the drone-based recording system. The speeds obtained from both methods were subsequently compared to assess measurement accuracy. The comparison revealed no  
Figure 5: Radar device installation on one of the locations. significant discrepancies between the radar and the drone-derived speed values, thereby confirming the reliability and validity of the drone-based speed measurement approach used in this research. The aerial video recordings at the selected locations were conducted using the drone during the period from 7 July 2023 to 8 August 2023, where the measurements were conducted during the week (Monday-Friday), excluding the weekend. [45]. The recordings were carried out during relevant off-peak hourly intervals, selected based on an analysis of hourly traffic flow fluctuations. Detailed information on the measurement periods is provided in Table 1.  
To determine the speed values, the aerial video footage was first converted into a format suitable for data processing, and then imported into the Adobe Premiere Pro 2023 software. Within this software, the video footage underwent detailed review, preprocessing, and analysis, during which the timepoints of the individual vehicles passing the entry and exit detection reference lines on each carriageway of the observed locations were identified. Upon a vehicle crossing the defined detection reference lines, the video frame's timestamp and the vehicle type present at the detection line were recorded (Figures 7-9) [45]. Figure 6: The unmanned aerial vehicle (drone) MAVIC 2 PRO, utilized for recording video footage of the selected locations [44].