The answers as to what is actually going on are already on this forum.If you're trying to train an AI system to identify objects in a video feed, yes. You train the AI with video feeds and training data.
Highways are the easiest target. While you're moving fast, they're also the most predictable. There are no stop signs on highways, no traffic lights, no pedestrian crossings, etc. Typically, lanes are much wider and the road condition much better than normal roads.
For Tesla to start moving towards full self driving or L4/L5, they're going to need to start training their cars on public roads. They're going to need to train it to see traffic signals and signs. They're going to need that video data.
Which is why it was concerning that Tesla recorded zero autonomous miles driven on California roads in 2017.
Finding them are an exercise left to the reader.
As a bonus, the answer that should alleviate your oh-so-genuine concern in California is also lurking around here.
Happy hunting!