VIENNA -- Authorities are investigating why a driverless bus struck a pedestrian in Vienna, an incident that resulted in minor injuries but stopped Austrian trials of the technology.

The Navya SAS vehicle was driving at 12 kilometers (7.5 miles) an hour on Thursday when it struck a 30-year-old woman in the knee, according to state broadcaster ORF.

Vienna's transit authority suspended further trials pending outcome of the investigation.

The city has been testing two driverless buses under a program that began June 6.

The Austrian Institute of Technology and Siemens mobility are also participating in the project, which required a professional driver on board when the units were operating.