Going electric with our transportation options is a crucial part of reducing greenhouse gas emissions, and e-scooters are one mode of transport emerging as an alternative to gas-powered cars for shorter trips. But how much difference do they actually make?

A new study puts it in precise terms: e-scooters can potentially save an average of 17.4 percent in travel time for people in the US. That's a big reduction in the time that might be spent in a car pumping out CO2 from its exhaust.

The research actually came about through a policy introduced in Atlanta, Georgia, in 2019: e-scooters and e-bikes were banned between the hours of 9 pm and 4 am in an attempt to improve public safety after a spate of accidents. Using the technology on board the shared vehicles, they could be locked out of a specific area at a specific time.

"I thought, okay, that's interesting because now we have near-perfect behavioral compliance in response to a policy intervention, which turns out to be extremely rare," says data scientist Omar Asensio, from the Georgia Institute of Technology.

"All of a sudden, if you're without the use of the scooter, what do you do? This created a great natural experiment, to be able to precisely measure the traffic times before and after this policy intervention and in doing so, test behavioral theories of mode substitution."

What Asensio and his colleagues found was that average commute times increased across the city by about 10 percent, while travel to stadium events (such as soccer games) rose by 37 percent on average – the equivalent of about 12 minutes per trip.

Adding up the additional time Atlanta's evening commuters all spend sitting in traffic, it works out as a potential 784,000 extra hours per year. The calculations were made with user data collected by Uber.

While the researchers didn't translate that directly into additional carbon dioxide pumped into the air, it's likely to be substantial. They did put a monetary figure on the extra travel time, estimating the economic costs of commuters sitting in congestion when e-scooters aren't available could total as much as $536 million a year for the US as a whole.

"We know that electric mobility will be the main contributor to decarbonizing the passenger transportation sector, therefore we need to understand the interactions between different modes of electric transportation," says industrial engineer Camila Apablaza, also from Georgia Tech.

Collectively known as 'shared micromobility' options – rented e-scooters and e-bikes you can hop on and hop off with the help of an app – are now available in more than 100 metropolitan areas in the United States.

There are questions over whether these travel alternatives actually reduce carbon emissions by getting people out of cars, or if they just replace other options such as walking and public transport. The research is ambivalent, finding it's complicated and depends on the location.

In Atlanta – one of the largest adopters of shared micromobility services – it seems clear that e-scooters and e-bikes have a direct impact on congestion.

At the same time the researchers are keen to point out the need for public safety to be prioritized in terms of city infrastructure and planning for these alternative modes of transport – the reason for the e-scooter and e-bike ban was because of hospitalizations and even fatal accidents involving riders and pedestrians.

"For physical infrastructure, land use and space allocation will require longer-term planning such as converting lanes usually reserved for cars into bike lanes that can be used for micromobility," the researchers write in their paper.

The research has been published in Nature Energy.