It's actually a decent idea, they're taking that dirty oil money and trying to build something sustainable and eco-friendly, if this works it could be used as a model for other cities/infrastructure. They coud license out the technology/companies to other countries.
It's essentially solving the urban sprawl problem, infrastructure problem, construction, pollution, global warming and conservation issue in one.
The key part is the train/transporation system. They should have multiple lines so that people can travel across the 'Line' without having to deal with too many stops.
How? This is all buzz words and CGI. Talking about autonomous this and AI that. So they plan to build a city as a line for what reason? Add smart AI that don't exists and other vaporware. The Saudis are looking forward to the end of oil which is good but you can tell some consultants sold them on this shyt and they'll probably come to their senses when there is billions down the drain and nothing to show for it
Because their population is expanding. Saudis have tons of kids.
Compress all city infrastructure into a single horizontal building. It's probably going to make construction less complicated to since you don't need a diverse array of materials for unique buildings, it's literally just one tall horizontal building with the same exterior for 170km. Transportation gets nullified, no more bullshyt roads and crap so therefore no emission of tailpipe exhaust. Lots of free space for solar panels and turbines, even geothermal energy.
Transportation is not nullified, the city is 105 miles long they plan to have highspeed trains. One of the biggest issue with all of this is that if there is an issue at any point on this line there is hardly space for a work around. The city is 200 metres wide, if a train were to derail, water main burst, major fire etc then the city is basically getting cut off at that point.
Another thing is just future growth like any other city it will need to grow and change imagine having to build new housing in the future and the cost of having to dig to keep on this straight line then extend the city wall before even build a new house.
The traditional city layouts that we know have been used for thousands of years for a reason