As Boeing and SpaceX develop spacecraft to take NASA astronauts to and from the International Space Station, the two companies are also coming up with ways to keep crew members safe in case future launches of these vehicles don’t go according to plan. Both companies have designed built-in abort systems into their spacecraft, which can carry the vehicles up and away from a malfunctioning rocket. But now Boeing has another option in case emergencies aries at the launchpad: an astronaut zip line.

Called the Starliner Emergency Egress System, it includes four cables that can rapidly carry astronauts away from Boeing’s launch site. The spacecraft Boeing is building, known as the CST-100 Starliner, is designed to launch on top of the United Launch Alliance’s Atlas V rocket, which takes off from a launch site at Cape Canaveral Air Force Station in Florida known as SLC-41. The cables are attached to the top of the crew access tower at SLC-41 — the structure the astronauts will use to climb to the Starliner when it’s on top of the Atlas V.

If for some reason the Atlas V starts malfunctioning just before launch, the astronauts can hop out of the Starliner and hop into specialized seats attached to the cables. They then ride down the cables, reaching speeds of up to 40 miles per hour during the trip. The riders are eventually deposited 1,300 feet from the launch site at a landing zone, and they can use hand brakes to slow down to a nice stop, according to Boeing. Otherwise, springs on the cables will automatically slow down the seats. While the system is mainly meant to help the crew, there are 20 seats available on the cables, so other personnel on the ground can also use the system if they’re nearby the launchpad.

too bad it’s only meant to be used during emergencies — seems like fun!

To create this system, ULA turned to the experts: a zip line company called Terra-Nova which creates a product known as the ZipRider. The same design for the ZipRider has basically been adapted for use by the astronauts when they ride on Boeing’s vehicles. “A modified, off-the-shelf product has been designed and constructed to meet our needs and reduce costs, while maintaining reliability and safety,” Gary Wentz, ULA’s vice president of human and commercial services, said in a statement.

ULA just conducted the final test of the system, so it’ll be more than ready by the time Boeing’s CST-100 Starliner starts carrying astronauts sometime in 2018. It’s too bad it’s only meant to be used during emergencies, though; it seems like a good way to pass the time before launches begin.