## Appendix A
### The Radar Sensors  
Anteral uRAD radar sensors, version 1.1, were used alongside Raspberry Pi 4, model B with 4 GB RAM. Micro-5D cards (16 GB) were purchased, with the Raspberry Pi operating system and uRAD software pre-installed. Technical support was also purchased. Table A1 provides an overview of the radar configuration parameters. Testing prior to the field trial is outlined in Figure A1 and Table A2. Collected test data and corresponding camera footage were sent to the supplier, who proposed recommendations for future testing. Table A3 details the parameters which were used in the field study. The supplier detailed the pre-processing steps taken before sensors store data to memory: The radar transceiver chip receives the reflected signal. The mixer mixes the received (RX) signal with the transmitted (TX) signal, and outputs in-phase (I) and quadrature (Q) components at Intermediate Frequency (IF). These two analog I/Q IF signals go through a low-pass filter, an amplifier stage and a high-pass filter. Filter values are proprietary. Subsequently, the analog signal is digitalized with an ADC at 25 kHz inmodes 2, 3 and 4. In the digital domain, the complex signal is formed, FFT obtained, and from it, range, velocity and SNR of detected targets are derived. The supplier also stated that calibration by the user is not needed, as performance is controlled in the lab prior to shipment, by measuring a constant distance of 1.5 m in mode 2. The combination of one Raspberry Pi attached to one uRAD radar board is here termed a _device_. The device was fixed to the interior of the windshield using a universal phone suction mount with a flexible arm, oriented such that the USB-C and micro-HDMI ports pointed directly upwards (cf. Figure A1). Since Raspberry Pi microprocessors were powered on and off using a USB-C cable, this orientation facilitated easy access and line of sight from above, for cable insertion and removal. It also made sure that the sensor did not detect the mount itself, being located outside radar field-of-view. Powerbanks and USB-C cables powered the devices at optimum voltage and amperage, while making data logging independent of truck power systems and status. This eliminated potential issues with undervolting and voltage spikes from in-vehicle outlets, while leaving flexibility for when logging start and stop had to be administered. Each Raspberry Pi had a Bluetooth USB dangle for a wireless keyboard and mouse, minimizing direct device contact. The dangle added an additional reason for ensuring stable power supply. The radar supplier confirmed that the dangle radio frequency would not affect radar operation. Along with the dangle, the micro-HDMI and power cables remained plugged into the device throughout the field trial. This allowed the devices to remain vehicle-mounted throughout both days, requiring only insertion and removal of the far-ends of the cables into the screen and powerbank for interfacing with the devices and powering them devices on and off, respectively. Radar output files never exceeded 5 MB, i.e., they were unproblematic with respect to SD card storage capacity. A battery powered portable monitor was used. With 30\({}^{\circ}\) vertical fields-of-view, 15\({}^{\circ}\) swept down from horizontal, so vertical sweep became 75\({}^{\circ}\), assuming sensors were mounted perfectly level. If trucks, with uRAD antennas at height \(h_{a}\), traversed a constant gradient road section, the road would be detected at a distance, \(d\), given Equation (A1):  
\[d=h_{a}\cdot\tan(75^{\circ})\] (A1)  
The presence of aftermarket dashboard tabletop surfaces required placing sensors at slightly different heights in each truck during the field study. With radar antennas at heights of 2.29 m (truck 2) and 2.15 m (truck 3), the road would be detected 8-8.5 m forwards. Having 30\({}^{\circ}\) fields-of-view also in the horizontal direction, radars also saw this far sideways at road level.