How does 50 toll booths make sense for a 4 lane highway?

Because passing through a toll booth slows down each vehicle, you can move more vehicles through the space with additional terminals. Unfortunately, when you've got peak traffic, the folks on the other side of the terminal can still create congestion as they merge back into the smaller lane.

The solution to this, from the Chinese perspective, is massive investment in High Speed Rail.

If you don't want to sit in traffic at a major tool entrance like this, you can just ride any of the 200 mph+ train routes crisscrossing the nation.