After March's fatal accident between one of Uber's self driving vehicles and a pedestrian, Uber has stopped all on-road testing and changed its plans. But the publication's sources claim that before the crash there was a dearth of investment in the simulation software, and lots of incompatible code between the autonomous vehicle software and simulation software Uber is developing internally.

The sources stopped short of saying there was a direct link between the lack of investment and the fatal accident involving one of Uber's autonomous taxis and a pedestrian.

At the moment the Unreal Engine-powered simulation software is still new and was not developed until after self driving project lead Anthony Levandowski was fired mid-2017.

But the report shows that there were some problems in the unit. Initially, there were differences in pay between simulation engineers and other engineers in the department. The end goal was to release a self-driving car in Arizona this year, codenamed "Roadrunner" to compete with Waymo's offering just outside of Phoenix.

Comparatively, Waymo has been touting its simulation testing for a while now. Last November, the company announced it'd logged some 2.5 million miles in its Carcraft simulation, on top of four million miles in the real world. Last year it was also revealed that Waymo's autonomous systems only required human intervention once every 5,128 miles versus Uber's nearly once per mile.