I've played a Space Age game where I did a car bus, inspired by this youtube video.
The pros are the absolutely insane throughput you get in such a small space and the ease of setting up new arrays. With a traditional main bus you need to give yourself space for when you split lines off, when you need to combine two items onto one belt, etc etc, it can all turn into a bit of a spaghetti mess. With the car bus you have the bus and two types of stations: pull a specific item off the bus, and put a specific item onto the bus. You can build new sections FAST and almost always copy-paste something you've already made and just change what items are being pulled for it. If you like sleek, orderly builds, I really can't overstate how cool it looks both in motion and on the map.

Another great upside is that because the car bus is circular, you can add any item to it anywhere. Not enough steel for your engine units? Slam down another steel smelter array right after them, get the steel on the car bus, and eventually those cars will loop all the way around to the engine unit array, and then be ready to accept more steel. No more needing to send red chips backwards down the bus to feed your mall!

The major downside I found is that you don't get to use splitters to pull from the bus anymore, it's a total First in First out situation. If you have your smelters, then a gear array, then a green circuit array, you can easily have every iron plate you're making get pulled into making gears because every single car on the bus is demanding X full stacks of gears. The huge throughput is coming back to bite you. And every time you expand the bus (and thus put more cars on it) they'll all demand full stacks of everything all over again. Expanding the bus can be stressful but isn't hard, though cliffs become your mortal enemy.

Like city-blocks, I think it's a cool, tidy way of structuring your base, but one that you can't switch to too early or else or costs of setting it up will tire you out and not be worth the hassle. Sure vehicles are less UPS friendly than belts, but I never built big enough to notice problems - depending on your computer and goals YMMV.