[adrianN]

A high speed train goes 300km/h, some can do 400. You'd need a huge tank in your car to make it go that speed for any amount of time.

Cars need to go slower because they have worse air resistance than trains and the tires get hot and wear out quickly.

[CamperBob2]

Airplanes are even faster... yet it's possible to drive from LA to SF in less time than it would take to fly, even if you never break the present-day speed limits. Remember, it's not fair if you count the distance from one city limit to another. You have to consider the time it takes a given passenger to get from their home or business to their end destination.

Also, all it will take is one (un)lucky 9/11-style terrorist attack, and everything we've come to know and love about air travel and the TSA will instantly apply to the train station. This is a matter of "when," not "if."

Finally, there's also a hidden economic cost associated with fixed tracks, similar to the costs/risks borne by someone who buys a house. They're stuck there. A homeowner might like to move to a nearby city to take a better job, but oops, they're still underwater on their mortgage. Likewise, locations and other trends in urban economic development shouldn't be biased by a decision made 50 years earlier regarding where to put the train tracks.

It's better to stay agile, and trains are perhaps the least agile things humanity has ever built.

[jacquesm]

You could conceivably space cars closely enough when they're automated that the aerodynamic drag would be considerably reduced for every car except the front one.

You're still going to have to deal with rolling resistance and going up-hill you'd have to limit the speed of such a convoy to the speed the slowest car can attain.

But for most distances that a car will normally travel the difference between 150 and 300 Km/h will not translate into meaningful changes in time spent on the road and probably you're still going to beat high-speed rail in door-to-door scenarios.