When electric scooters flooded into Austin, the companies that rent them touted their environmental benefits: “Riders were able to prevent 445,334 pounds of carbon emissions,” a press release from Bird said. The startup LimeBike estimated its scooters reduced 8,500 pounds of CO2 here in just two weeks.

But those numbers are based on some shaky assumptions.

KUT's Mose Buchele reports

Sam Sadle, LimeBike’s director of strategic development, said his company assumes most scooter users are riding them instead of riding in cars. Bird said it assumes half its scooter rides are replacing a one-mile car ride. So, are scooters replacing car trips?

“We honestly don’t know yet,” said Phil Lasley, who studies traffic, bicycle and pedestrian issues with the Texas A&M Transportation Institute.

He said it's possible scooter rides are replacing short drives, but they could be replacing other modes of transportation, too.

“Are these trips taking away from other bicycle trips? Are they taking away from transit? Are they taking away from walking?” Lasley said. The technology is so new that people don’t know.

But that doesn’t stop people from making educated guesses.

Haje Jan Kamps published a piece last month on TechCrunch, outlining the financial assumptions e-scooter companies need to make for their business models to succeed.

Kamps, the director of portfolio at the venture capital firm Bolt, said the startups are in a desperate fight to win riders. (He said the firm has no investment in any e-scooter companies.)

“They are currently in a massive scaling mode,” he said, “and so the only concern they have, really, is to get as many scooters on the roads as possible, and as many rides as possible for each individual scooter.”

Depending on how sturdy the scooters are and how often they’re thrown out and replaced, that could be bad news for the environment.

“So the way this pans out is the only thing you care about it growth at any cost,” Kamps said. “There is a real risk that some of the things like re-usability or recyclability might be first on the chopping block.”

“Not so!” say scooter companies.

“I like to say that we use every part of the buffalo,” said Anthony Fleo, regional general manager for LimeBike in Austin. He said even when a scooter needs to be scrapped, its working parts are retained for use on other bikes and scooters and for spare parts.

Fleo estimated LimeBike scooters have a two-year lifespan – but that depends on the use they get.

“It appears that these services are being heavily used,” Lasley said.

He said the more popular scooters become, the more they may end up in the waste stream, even if they reduce CO2 emissions.

And again, that’s if.