Use OpenCV with in-game camera to detect road lanes

I am trying to implement a traffic system, with AI cars. I need the cars to detect lanes, know when they change lane, follow them, and recognize intersections.

The last few days I am looking for image processing techniques and I found out about openCV and that it can be used in Unity. I have seen many videos and examples but all of them use a webcam. How can I use the in-game camera for all the image processing and what is the best techniques to detect road lanes? Anything to help me start?

I am actually trying to do something like this, entirely within unity: https://www.youtube.com/watch?v=kIgbuksFguI

(The city and the car behaviors are already implemented)