## 5 Experimental Section
### Experimental Setup  
The experiments are performed at an urban road site shown in Figure 12. Two southbound lanes A and B and two northbound lanes C and D are at the site. Each lane width is around 3.5 m. Separation blocks lay between lanes B and C. Since there are separation blocks between lanes B and C, only the borderline between lanes A and B, and that between lanes C and D are considered in the proposed algorithms. The FMCW TMRD (UUEI, Taoyuan, Taiwan) with a 10-GHz frequency band is utilized for the experiments because it is accessible to us, and is commonly and commercially used. However, the TMRD can have only one algorithm equipped for vehicle detection at each time. Therefore, we cannot use one TMRD for the performance comparisons of several algorithms using the same received signal inputs at each time. To tackle the aforementioned situation, two TMRDs are deployed as shown in Figure 13 for testing the performance of two algorithms at each time block. FMCW transmissions by the two TMRDs are synchronized. Besides, the two TMRDs are close to each other and placed at 4 \(\sim\) 5 m in height. It is ensured that the two TMRDs can operate simultaneously without mutual FMCW interferences. No extra space at the site is available for the deployment of a third TMRD so  
Figure 12: Urban road site for traffic experimental tests. (**a**) Road site viewed fromthe sideway; (**b**) Road site viewed from the deployed TMRDs. that the height requirement and limitation can be met. This is because many business advertisements excessively occupy building walls. To begin with, we properly set thresholds for the proposed and conventional methods. This is achieved empirically as follows. For several days, we observe and record many FFT magnitudes of environment noise within the detection zone of each lane under the conditions with no vehicles or with vehicles. To demonstrate this, we display Figure 14. Figure 14a is a snapshot of those observations within the detection zone of each lane under the conditions with no vehicles while Figure 14b is under the conditions with vehicles. Subsequently, we approximate the average of ensemble FFT peaks of noise within a lane as the threshold value corresponding to the lane. As a result, 22, 21, 15 and 15 are given as threshold values for lanes A, B, C and D, respectively. Figure 15 is a snapshot of the edged FFTs of received vehicle signals and clutter after the threshold values are applied. The threshold value for the conventional method is chosen as 31 because for many times, the value 31 is instantaneously observed and recorded as the overall maximum FFT peaks of noise within all lanes. An instance is shown in Figure 14b. Though the aforementioned threshold selection process is utilized for our experiments herein, it can also be used at other test sites. However, selected threshold values for one site can be very different from those for the other places. Figure 14: Threshold selection for traffic experimental tests. (**a**) A snapshot of FFT magnitude of environment noise within each lane with no vehicles; (**b**) A snapshot of FFT magnitudes of both environment noise and vehicle signal within each lane. Figure 13: Two TMRDs deployed at the road site. For each method, the detection accuracy of lane vehicle flow (LVF) for lane \(i\) with \(i=\mathrm{A,B,C,D}\), is evaluated based on  
\[\mathrm{LVF\ accuracy}=(1-\frac{|\mathrm{actual\ vehicle\ no.\ of\ lane\ }i-\mathrm{detected\ vehicle\ no.\ of\ lane\ }i|}{\mathrm{actual\ vehicle\ no.\ of\ lane\ }i})\times 100\% \tag{5}\]  
For each method, the detection accuracy of directional traffic volume (DTV) for lanes \(i\) and \(j\) with \((i,j)=(\mathrm{A,B})\) or \((\mathrm{C,D})\) is evaluated based on  
\[\mathrm{DTV\ accuracy}=(1-\frac{|\mathrm{actual\ total\ vehicle\ no.\ of\ lanes\ }i\ and\ j-\mathrm{detected\ total\ vehicle\ no.\ of\ lanes\ }i\ and\ j|}{\mathrm{actual\ total\ vehicle\ no.\ of\ lanes\ }i\ and\ j})\times 100\% \tag{6}\]  
The actual vehicle no.