[jemfinch]

> At some point, every available square foot of roadway is filled with a car. AI can help limit the amount of extra space taken up by air, but that will only moderately increase the number of cars that it will take before traffic hits. That number of cars will be reached, easily.

The thing to keep in mind is that AI can limit the extra space between the cars as well as increase the speed those cars can safely travel. The cars will spend substantially less time on the road because they'll be going faster. Double the speed and you've converted a 60 minute commute into a 30 minute commute, doubling the number of commuters the roadway can support even if you don't adjust inter-car distance art all.

[jeremysmyth]

Don't forget Amdahl's law though. You might be able to optimize away the reaction time with good AI, but you can't optimize away mechanical factors like engine failure, tire grip, and road surface friction. This affects the maximum speed and traffic density just like a human's reaction time.

This means that if one car in a densely packed column fails (blowout, engine seizure, ...) then the car immediately behind it is still subject to its mechanical ability to avoid a collision (swerve into empty space or brake to a hard stop at speed) no matter how fast it reacts.