1973 IDAHO TRANSFER (Time traveling youth escape ecological catastrophe)

Teenager Karen Braden (Kelley Bohanon) is a troubled mental hospital outpatient who is taken by her father George and sister Isa to a government facility near the Craters of the Moon lava fields in Idaho. The project there was commissioned to develop matter transference, but made a different discovery: time travel. They also discovered that a mysterious ecological catastrophe will soon wipe out civilization. The time travel process has negative health effects, though. Adults "not much older than 20" are unable to survive for long, as their kidneys hemorrhage shortly after the experience. So the scientists decide to only send young people 56 years into the future so they can build a new civilization. After the government takes over the project, the transfer machines are turned off, trapping a large number of project members in the future. Now trapped, they begin exploring the future world. The last survivor from the project is picked up by a family dressed in futuristic clothing. She is placed alive in the trunk of their car, to be used as fuel. The small girl in the back seat asks what will happen when they run out of them (people from the past), "Will we have to use each other, then?"
https://en.wikipedia.org/wiki/Idaho_Transfer