90% of long-haul trucking may soon be self-driving. Are you ready to share the road with an autonomous 18-wheeler?

Elon Musk has called them the most impactful technology on the horizon. But unions are lobbying against their widespread use, citing studies showing they may kill up to 500,000 jobs.

They are autonomous trucks, which supporters pitch as the remedy to a growing demand for shipping and for greater safety on the road. If the technology becomes good enough, the logistics industry will be radically changed, with trucks operating nearly around the clock as they criss-cross the country.

The number of companies racing to perfect automated trucking technology is long. Last year, Tesla revealed plans for its own autonomous truck called
Semi, which relies on battery power and has a range of up to 500 miles. Meanwhile, Daimler, one of the world’s largest trucking companies, has announced a $573 million investment in self-driving trucks. And the startup Aurora has created its own autonomous truck operating system.

Still, it will be years before drivers are completely absent from behind the wheel of 18-wheelers, experts tell Fortune.