“The rule of thumb is can it be for everyone.”
One hundred years ago the world got connected. Because of this people were able to see what was happening from a global view, not limited by national and cultural restraints.
Cities were found to be unsustainable and the great migration soon followed, decentralising everything. Changing everything for the better, except for getting around quickly.
It used to take a day to go around the world, now it takes months. Since everyone is living sustainably there's no need to transport any goods of any kind except for seeds of new varieties of plants and trees.
Lots of people came up with lots of ways to travel at high speed without damaging the environment until you apply the rule of thumb. Can it be for everyone? The answer is no, so high speed travel can only exist in an elitist centralised world that inevitably will lead to the oppression we've left behind.
Cycleways became the fastest way to get around. Every kilometre there's a funnel to catch the wind and a chimney stack for the air to exit. The cycleway has an upper and lower deck each going in different directions. The upper deck and the chimney are heated by the sun during the day. This creates a wind of up to fifty kilometres an hour, at night it drops down to around twenty kilometres an hour. Air comes in the funnel, travels one kilometre through the upper tunnel and then travels back through the lower tunnel and out the chimney.
With five bikes all linked together and clicked onto the cycleway's rail and a tail wind of twenty kilometres an hour, very little effort is needed to reach fifty k's. During the day with ten cyclists, speeds of over one hundred k's are easy. The record speed of one hundred and eighty k's was set with forty cyclists. With only a single lane there's no overtaking, so slow riders and people who can't pedal at all get pushed along by faster ones.