TLDR; AirSim is simulation software built upon Unreal Engine 4 from Microsoft Research. It now includes car simulation and real city-like environment where you can test your self-driving algorithms. You can just download the binaries and start calling its Python APIs in minutes.
Is this same as Udacity car simulator?
Not quite... I think Udacity's simulator is built on Unity and the environment it runs in is probably not as big and detailed.