”Obayashi envisages a space elevator using six oval-shaped cars, each measuring 18m x 7.2m holding 30 people, connected by a cable”
I can’t see how one would read that other than as each car holding 30 people.
You would need an extra comma to make it six cars holding 30 people in total:
”Obayashi envisages a space elevator using six oval-shaped cars, each measuring 18m x 7.2m, holding 30 people, connected by a cable”