I'm assuming the automated cars will bunch up together and drift off each other.

Correct. But riddle me this: when you're driving down the freeway, do you maintain a safe following distance? Or do you tailgate?

With a pilotless vehicle, the "safe following distance" is the "tailgating" of a piloted vehicle. Works great when you've got pilotless vehicles following other pilotless vehicles. Kind of comes apart at the seams when you've got a piloted vehicle following a pilotless vehicle.

Consider the implications. I head out onto the 405. I'm the only person driving in a sea of Google Priuses. My safe following distance is the two second rule - at 70mph, that's 205 ft. call it 10 car lengths.

The Google Priuses, however, are automated. Are infrared, laser and radar. Are running 8 cores at 3.5GHz. They're rawkin' a quarter-second rule, but for safety's sake, they're going for a half second. That's 50 feet.

From a "traffic" standpoint, we just got 4 times as many cars on the road. So that's pretty dope. But here I come!

The first thing that happens is that Google has no idea who I am or what I'm going to do. So anything that senses me is going to go "OH SHIT HUMAN" and make a little bubble around me. If it's clever, it'll give me the space to merge, to change lanes, to pass, to do whatever I need in 'human' spacing. So for the area directly around me, my density goes down to what it was originally.

But Google has to do that for any vehicle that isn't part of its network. It has to presume that an object it cannot control is a lowest-common-denominator vehicle. It can tailgate the hell out of me... but I'll bet it doesn't. I'll bet that ends up being against the law, same as if Google were a person.

Here's where the math gets interesting. I have no idea at what mix the traffic becomes dominated by "human accommodation." Your network also has to deal with merging "human bubbles" even where it is efficient. Throw a little snow on the road and all of a sudden these people that have been blissed out, stoned, and playing Words with Friends for the past 20 minutes are suddenly at the wheel of a vehicle on an icy road.

And all this presumes that the system works as designed, works as intended. Google has FUCKED the 405 for the past few weeks because they started integrating Waze into their routing. Which means anybody using Google Maps during rush hour gets "In 600 feet take the off-ramp" even if they're 4 lanes over. It ain't pretty. Plenty of people are stupid enough to try.