A commenter complained that he would not want to sleep on a one-gravity loop system on Mars, the Moon or elsewhere in space with low gravity or no gravity. The other complaint was that it would be too costly to build and maintain.
1. San Francisco spends $923 million to $3 billion per mile for regular subway extensions of the BART rail system
When the Salesforce Transit Center opened in San Francisco summer 2018 a new tunnel will be needed to connect it to the current Caltrain terminus in SoMa. The project, known as the Downtown Extension, is estimated to cost $3 billion for each mile of the subway, six times more than the average outside the United States. The Central Subway, a 1.7-mile tunnel that will connect Chinatown to Fourth and Brannan Streets, is a relative bargain at $923 million-per-mile. But elsewhere in the world, new subways cost half as much.
2. People pay for the comfort and romance of overnight sleeper cars on tourism trains. A 500-meter train loop can comfortably provide the simulation of gravity. People would be in sleeper cars if they needed the overnight one-gee.
Sleeper cars on trains have been around since the early 1800s. Tens of thousands of people use them every year. People pay extra for the private cabin and tourism experience to watch the country side.
Solutions do not have to be uncomfortable or costly. Also, current solutions can be insanely costly. Starting fresh without costs for land rights, legal issues can make things two hundred times cheaper. This is one of the huge advantages of building on the moon and Mars. There is only transportation costs but no land costs and virtually no bureaucracy for decades.
SOURCES- Interesting Engineering, Boring Company, Wikipedia
Written By Brian Wang, Nextbigfuture.com