July 19, 2019—Authorities are investigating why a driverless bus struck a pedestrian in Vienna, an incident that stopped Austrian trials of the technology, according to a report by Bloomberg.

The European city has been testing a pair of driverless buses under a program that began earlier this summer. The Austrian Institute of Technology and Siemens mobility are also participating in the project, which required a driver onboard when the units were operating.

The bus struck a 30-year-old woman in the knee, according to the report.