*4.3. Integrated Equation*

In the preceding two subsections, equations have been proposed for distance measurement on straight and curved roads. The radius of curvature of the curved road is inversely proportional to the difference between the measured distances on the straight and curved roads. Therefore, if the radius of curvature is larger than a certain threshold, the curved road can be assumed to be approximately straight without a significant loss of accuracy. When the radius of curvature was 1293 m, an error rate of at most 0.1% was observed. Therefore, 1293 m was adopted as the aforementioned threshold in the proposed equation. This is written as follows:

$$Z\_t = \begin{cases} Z\_\S & R > 1293 \text{ m} \\ \text{arc} & R \le 1293 \text{ m} \end{cases} \tag{7}$$

where:

*Zt*—the distance between the vehicle and the object in front of the vehicle.

#### **5. Vehicle Test and Validation**

*5.1. Vehicle Used for Vehicle Test*

The vehicle test was conducted to verify the accuracy of the forward distance measurement equation after mounting the dual camera setup at the optimized positions. H company's Veracruz (Figure 14) was used as the test vehicle, and its specifications are listed in Table 2.

**Figure 14.** Test vehicle.

**Table 2.** Specifications of the test vehicle.


The dual cameras were mounted on the front bumper of the vehicle used for the test, as depicted in Figure 15. Each camera was a Logitech C920 HD Pro Webcam, and its specifications are listed in Table 3.

**Figure 15.** Test device.

**Table 3.** Specifications of cameras.


#### *5.2. Vehicle Test Location and Conditions*

Because of safety considerations, the vehicle test was conducted within the Seongseo Campus of Keimyung University, located in Daegu Metropolitan City, Korea. Figure 16 depicts the straight and curved roads utilized for testing. The radius of curvature of the curved road was 69 m; it was calculated as the radius of a planar curve based on the design speed defined in article 19 of the rules for the structure and facility standards of roads, which are presented in Table 4. A curved road with a radius of curvature of at most 80 m was selected, considering the driving speed limit of 50 km/h in the city.

**Figure 16.** Vehicle test roads: (**a**) straight road, (**b**) curved road.


**Table 4.** Minimum radius of curvature for curved roads according to the design standards.

In the case of the straight road, stationary and driving states were classified using obstacles installed at intervals of 10 m between distances of 10 m and 40 m in front of the vehicle. In the case of the curved road, the two states were classified using obstacles installed at 5 m intervals between 6 m and 21 m in front of the vehicle along the center of the road and on the left and right lane markers. The entire test was conducted corresponding to a total of four cases.

The tests were repeated three times using the same equipment to acquire objective data. The environmental conditions during the experiments are summarized in Table 5. There was no variation in the weather.

**Table 5.** The environmental conditions.

