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Table 1 Summary of observed vehicle behaviours, possible reasons, applied solutions and occurrences

From: Digibus©: results from the first self-driving shuttle trial on a public road in Austria

Observed behaviour Possible reason Applied solution Occurrence
Shuttle stopped for obstacle • Parking vehicles on the roadside or at bus stops • Bypassing the obstacle manually
• Setting the shuttle to automatic mode after the obstacle
• Frequent
Shuttle stopped for no apparent reason • Branches of trees or shrubs on the roadside
• Wrongly detected obstacle
• Unreliable positioning
• Sensor reflections due to water lacquers, heavy rain or snowfall
• Setting the shuttle to automatic mode again for continuing the test drive
• If this was not successful, driving back manually to a safe parking position (e.g. bus stop)
• Frequent
Detection of other road users failed • Velocities > 30 km/h of approaching or passing vehicles at left turns or exits from bus stops or side roads
• Dead angles of 360° LIDAR sensors due to vehicle’s own shading
• Low spatial resolution of the Velodyne VLP-16 LIDAR sensors
• Stopping the shuttle and taking over manual control • Frequent
Unclear interaction with other road users • Planned safety stops
• Stopping without any reason
• Is overtaking safe?
• Abandoned priority
• Missing trust by other road users
• Variable messages on the back screen of the vehicle
• Using hand signs if possible
• Frequent
Shuttle could not be set to automatic mode after a stop • Vehicle being out of driving path
• Software problem
• Driving manually to the next safe parking position (e.g. bus stop)
• Applying one or several restarts
• Contacting the Navya supervision team for solving the problem via remote control
• Several test drives