# Driverless Bus Path Tracking Based on Fuzzy Pure Pursuit Control with a Front Axle Reference
## 4 Real Bus Experiments  
A driverless bus system is built in our early work [15]. The global path-planning and local path-planning are available in this implementation. Figure 19a shows the overview of the driverless bus (12 m \(\times\) 2.57 m \(\times\) 3.28 m, provided by CRRC ELECTRIC VEHICLE CO., LTD, ZhuZhou City, China). The wheelbase is 5.9 m. As Figure 4 shows, GPS (IMU) is equipped, which gives the position, heading angle, and velocity of the driverless bus. The driverless bus stays in its lane in Figure 19b,c. Additionally, the driverless bus makes a U-turn in Figure 19d,e.  
The lane-keeping experiments are carried out to illustrate the advantages of PPC-FAR. The length of the target lane is 2 km, and the curvature is less than 0.01. The initial velocity is 0 km/h, the target velocity is set as 20 km/h. Meanwhile, the initial lateral error is 1.5 m, the initial heading error is close to 0. According to the experiments in Section 3, \(l_{d}\) is defined as 15 m, and \(k\) is 1. The performances of PPC-FAR and PPC-RAR are shown in Figure 20.  
Figure 19: Real bus experiments. (**a**) Overview of the driverless bus. (**b,c**) Lane-keeping. (**d–f**) U-turn.  
Figure 18: Longitudinal control simulation results. (**a**) Simulate scene. (**b**) Desired velocity and actual velocity. (**c**) Velocity error. (**d**) Deceleration of the driverless bus.  
Figure 20a shows the steering angle of PPC-FAR and PPC-RAR. The lateral error is shown in Figure 20b. Obviously, there is almost no error between the actual steering angles and the desired steering angle. Additionally, the steering angles reach \(-6^{\circ}\) to reduce the lateral error in the beginning. The overshoot in PPC-RAR is obvious but there is no overshoot in PPC-FAR. Meanwhile, the lateral error of PPC-FAR is larger than PPC-FAR. The oscillation in PPC-RAR is not obvious in Figure 20, but it is marked if sitting in the bus. When the driverless bus is controlled by PPC-FAR, the bus moves forward smoothly, and the oscillation is hardly felt.  
The results of the lane-keeping experiment are similar to the simulation results in Section 3.1.1. Those results show better stability of PPC-FAR under low speed conditions. Meanwhile, the tracking accuracy is also improved.  
Another real bus experiment is shown in Figures 21 and 22. There are two straight lanes and a curve which are shown in Figure 21a. The slope of the road is shown in Figure 21b. The first lane is downhill and then there is a curve. The second lane is uphill.  
Figure 21: The experiment scene. (**a**) Desired path. (**b**) Road slope.  
Figure 20: Lane-keeping experiment in a real driverless bus with PPC-FAR and PPC-RAR. (**a**) Steering angle. (**b**) Lateral error.  
Figure 22a illustrates the desired path and the actual path of the driverless bus. Meanwhile, steering angles and lateral errors are indicated in Figure 22b. During turning, the maximum lateral error is 0.5 m, and the results are similar to the simulation in Section 3. The parameters are instructed in Table 6. \(k\) and \(l^{\prime}{}_{d}\) are determined by the fuzzy logic inference machine. Since the model in TruckSim does not describe the real bus well and the real bus requires less time to slow down, the parameters in Table 6 are different from Table 5.  
Additionally, the desired velocities and feedback velocities are illustrated in Figure 22c. The initial velocity is 23 km/h, while the velocity reduces to 10 km/h in the turning process. The decelerations and longitudinal errors are illustrated in Figure 22d. Since the feedback of the velocity is discrete and the noise is unpredictable, the longitudinal errors fluctuate. Additionally, the deceleration is continuous and the maximum deceleration is 0.8 m/s\({}^{2}\). Conclusively, the experiments in the driverless bus verify the simulation in Section 3 and indicate the good performance of PPC-FAR.