I'm impressed with this self-driving on California's spacious streets in perfect weather. I'll be really impressed when I see a self-driving car go down a London street in pouring rain, realize it needs to allow someone to come from the other direction and reverses and moves to the left to allow them through.
tl;dr: don't trust the client (or other drivers).
And on the other hand there is plenty of opportunity to include encryption with gov/mfn signed keys, crosscheck received data with sensor values, etc.
The benefits far outweigh the risks.
People seem to hand-wave and make up what these supposed future self driving cars will do - and worse, they hand-wave and assert they'll be objectively better at X than humans, without any evidence to backup the assertion.
Self driving cars are made by fallible humans using fallible programming languages and constructs. They can't possibly account for every situation or scenario - but people hand-wave and say it magically will.
Sure, one day you'll be able to sleep in the back seat of your car or read a book while it precisely weaves you between traffic only to navigate you right off a cliff. Or the neighbor's kid with a laser pointer prevents your car from turning into the driveway.
Driver-assisted cars are the real future.
In the case of cars some radio comms (uhf, wifi, or even bluetooth?) is probably sufficient since there is no reason for a car in New York cares about the opinions of a car in San Francisco. You'd probably even see performance gains under a distributed system since latency is effectively taken out of the equation (time of flight for local radio being effectively instantaneous).
> Maybe it will have technology to not go on that street until it is good to do so.
It's not technology that's required, barring perhaps flying car technology.
If every way is busy, you can't just wait eternally, you have to communicate with other drivers as parent commenter said, maybe let a couple of people go, and then realise when you just need to go for it and 'force' someone to wait for you if they're not otherwise going to.
It will be really awesome to see a car do that safely and autonomously.
There'll come a time, perhaps, when two cars are flashing their headlights at each other to communicate, for no real reason other than "that's how human-driven cars did it in the old days"!
NB I'm sure "proper" behaviour can be programmed - I'm just keen to see it! (And who waives if it is a self driving car?)