## 3 Results and Discussion
At the same time, it makes the axle of the front wheel range between \(\pm\)45\({}^{\circ}\). The feedback to the lateral control system is obtained by means of actual (lateral) position information in the form of the angular position (obtained from the different sensing possibilities: GPS, magnetometers, encoders, etc. ), which is compared with the angular position command. Figure 13: Longitudinal and lateral control scheme. The results of longitudinal control for one of the experiments can be noticed in Figure 14, where a comparison among the speed of the vehicle, the position of the brake and the acceleration along the longitudinal axis (bus forward motion) obtained through an IMU installed on the front axle is presented. In this experiment and during most of the trajectory, the commanded speed was about 10 km/h, because the test lane contains small radii of curvature and slopes. In the last trajectory segment of the test lane (straight line), the speed was increased up to 20 km/h. It can be noticed in Figure 14 that 25 s after the start, the brake system applies a brake signal to check if the system is working properly. Then, the main application of the brake controller is to regulate the speed commanded mainly during the downward slope section. This takes place between the times 125 and 300 s, approximately. It can be noticed in Figure 14, for this period of time, that the brake signal (and correspondingly, the acceleration signal) shows an oscillation due to the chosen algorithm for the brake system, where a command signal in the shape of a saw-tooth is entered into the brake controller, which acts as a Proportional-Integral (PI) action and provides a comfortable sensation of very near constant speed, as should be expected. Figure 15 shows the experimental results obtained by applying the lateral control of the bus for tracking the required trajectory. This figure shows the steering command, the lateral acceleration of the bus and the angular rate on the \(z\)-axis (azimuth). The angular rate sensor follows the curves of the trajectory commanded by the bus steering. The azimuthal speeds have been measured at two different points; the first, on the bus front axle, and the second, on the rotatory junction of the bus, in order to know both characteristics of its behavior. One of them is to know the position of the last section with respect to the first section of the bus. The lateral acceleration signal can be used in a feedback loop lateral control to improve the tracking of the trajectory. Using this signal in the control system, small lateral movements will be diminished. Figure 14: Comparison among bus speed, brake position and x-acceleration during the tracking trajectory. Brake control is applied 25 s after the start and from the times 125 to 300 s to cope with a downslope in the circuit. The lateral error during the trajectory tracking was relatively small and within the safety margins established in the control strategy. Figure 16 shows that the maximum peaks of the lateral error were approximately 0.35 m, these peaks being located in the smallest curvature radii sections, where the bus front is more separated from the theoretical trajectory to precisely cope with the curvature. During most of the trajectory, the lateral error was about or less than 0.10 m, which is acceptable for a bus of these dimensions. Many experiments have been performed within the CSIC experimental test area. Figure 17 illustrates the automatic control of the articulated bus following a required trajectory. The steering wheel angular rotation experimental data are shown as the correlation with the real trajectory. In this  
Figure 16: Lateral error during the tracking of the test lane. Figure 15: Comparison among steering command, lateral acceleration and angular rate in the \(z\)-axis during the tracking of the trajectory.