GNSS-Based Driver Assistance for Charging Electric City Buses: Implementation and Lessons Learned from Field Testing  
[PERSON]  
1 Institute of Robotics and Machine Intelligence, Pozznat University of Technology, 60-965 Poznan, Poland; [EMAIL_ADDRESS] (I.E. ); [EMAIL_ADDRESS] (K.C. ); [EMAIL_ADDRESS] (M.R.N.) [PERSON]  
1 Institute of Robotics and Machine Intelligence, Pozznat University of Technology, 60-965 Poznan, Poland; [EMAIL_ADDRESS] (I.E. ); [EMAIL_ADDRESS] (K.C. ); [EMAIL_ADDRESS] (M.R.N.) [PERSON]  
1 Institute of Robotics and Machine Intelligence, Pozznat University of Technology, 60-965 Poznan, Poland; [EMAIL_ADDRESS] (I.E. ); [EMAIL_ADDRESS] (K.C. ); [EMAIL_ADDRESS] (M.R.N.) [PERSON]  
1 Institute of Robotics and Machine Intelligence, Pozznat University of Technology, 60-965 Poznan, Poland; [EMAIL_ADDRESS] (I.E. ); [EMAIL_ADDRESS] (K.C. ); [EMAIL_ADDRESS] (M.R.N.) some mechanical adaptation to ensure proper connection, repeated inaccurate docking manoeuvres impose additional strain on the connecting components and can contribute to the faster wear of the collector strips and other components. An advanced driver-assistance system (ADAS) can solve the problem by providing visual cues to the driver. Following these cues, the driver can steer the vehicle along a proper trajectory ending in a position convenient for docking. The ADAS adheres to the Society of Automotive Engineers (SAE) automation level 1 [4]. Although a bus with ADAS is not autonomous, this system can reduce driver stress and compensate for limited experience. In earlier works [3; 5], we described the general concept of our ADAS system for single-segment and articulated buses, along with motion-planning and control subsystems, and a method for localising the bus relative to the charging station using a single camera. The research described there involved technology demonstrators developed as part of a research project carried out by Poznan University of Technology together with Solaris Bus & Coach, which is one of Europe's leading electric bus manufacturers. In contrast, this article deals with extensive implementation tests of the ADAS system supporting docking to electric chargers, which were carried out with the assistance of the MPK Poznan Sp. z o.o. transportation service from November 2022 to March 2023. These tests concerned an example of the Solaris Urbino 12 Electric single-body bus equipped with the production-ready variant of the ADAS system, which was subject to significant changes with respect to the versions tested earlier. The need for changes resulted from an economic analysis of the profitability of implementing a vehicle with additional equipment. As a result of this analysis, external sensors such as a camera or laser scanner were removed, basing the operation of the ADAS system entirely on GNSS (Global Navigation Satellite System) data and readings from the bus's existing sensors (steering angle, driving speed) accessed via the CAN interface. Although the chosen sensory configuration without any external sensors (LiDAR, camera) makes it impossible to monitor the close environment of the bus for dynamic obstacles, this configuration is much more practical to maintain on a retrofitted bus, while the safety of manoeuvres in a SAE level 1 system is still ensured by the driver, who is responsible for monitoring the environment as during docking manoeuvres without the support from ADAS. There are potential drawbacks to relying solely on GNSS data for precise manoeuvres, such as signal blockages or multipath effects. However, according to the results of our tests, the only failure mode that needs to be considered is the close vicinity of tall buildings or trees with dense canopies that may block the satellite view, thus decreasing the localisation accuracy. Considering that charging stations are not deployed in such locations due to safety considerations [6], our choice of the localisation system is justified.