Carla – Open-source simulator for autonomous driving research
carla.org
carla.org
On seeing the name, I had hoped it had come out of Udacity and their Self-Driving Car Engineer Nanodegree program; I was a "beta-tester" for that course (read: in the first cohort of the new nanodegree), and the self-driving vehicle that was being developed as a part of that course had the same name.
As far as I know, the simulator and code and other stuff we used is all available on github:
https://github.com/udacity/self-driving-car
https://github.com/udacity/self-driving-car-sim
Not as advanced, of course, but still another open-source avenue with a similar purpose. As I recall, it wasn't very difficult to work with, and even with a GTX 750 TI/SC GPU I was able to both render, train, and run models and still have 3D acceleration using CUDA on my Ubuntu install. Of course, that maxed out the GPU and put the fans on high, but it still worked fairly well at a decent resolution and level of detail settings. Just to show you don't need an expensive GPU to play around with this stuff...
You can even simulate weather!