Trains of cars
Jut replying here because it’s hard to comment on Twitter due to size limitation.
Your initial quote is that it would be more efficient for cars to drive at 100mph and be distant by 20 foots. It’s wrong because the most efficient speed for a standalone car is around 50mph, with acceptable tradeoff until 60mph.
Now, you’re totally right we should allow people to move faster, because it just makes sense. Trains of cars you described will definitely exist, and the reason is that riding close to each other will reduce the dynamic friction by much, as the first vehicle takes most of the friction and “opens the way” to the following one, if they ride close enough (~10ft).
This means we could reach the efficient speed of the motor, or be close to it (that’s about 80mph). Maybe if we accept reasonable losses, may allow speeds up to 90mph or something like you propose but that’s not sure for practical reasons.
Still there’s a catch: you can’t get all cars to follow each other tightly because when you need to exit the road, you’ll have to cross the road of drivers from the other lanes, and those will ride much more slowly.
As a consequence, trains of cars will have to be limited in size (~10 cars) and will be located on the rightmost lane. The other lanes will have distance between cars similar to the ones we know now, if not more closer to highway exists, to allow those cars to insert into traffic without forcing every car on the other lane to brake and loose energy.
To sum up: for large distances, we may see road trains on the rightmost lane of highways with a possibly higher speed than we enforce now. The catch is that this only works well if the highway is not congested, as in case the middle lane is too busy to allow large rooms between cars, the speed limit on the rightmost lane will have to be equal to the one on the middle lane, to allow seamless insertion of road trains exiting the train lane.