Confirming rumors that have been swirling for some time, on-demand electric scooter and bike startup Lime today announced that it has closed a $310 million series D financing round led by Andreessen Horowitz, Bain Capital Ventures, Fidelity Investments, GV, and IVP.  It values the company at a whopping $2.4 billion — double the previous valuation of $1.1 billion.

Existing investors Alphabet, Coatue, Fifth Wall, GGV Capital, Singapore’s GIC, and others participated, along with several new investors including GSV Capital, FJ Labs, Bling Capital, Europe’s GR Capital, and St. Augustine Partners. CEO Toby Sun said the funding will be used to expand Lime’s service into new markets, enhance its technology, grow its team, and pilot “new opportunities.”

“This new investment demonstrates the fundamental strength of our business and the increasingly rapid adoption of Lime,” Sun wrote in a blog post. “We will also continue investing in two critical areas: rider safety and city collaboration.”

The infusion of fresh capital comes as Lime sees its popularity soar in the 15 countries and the hundreds of cities, towns, campuses, universities, and communities where it’s available. The ten million people who’ve signed up for service have taken 34 million trips, and Lime says it’s recorded a 5.5 times increase in trips in the past seven months alone.

Lime, for the uninitiated, offers bicycles and electric scooters (through a partnership with Segway) that sport tech such as GPS, airless tires, and electronic locks, enabling them to be picked up and parked anywhere. It’s also working on a “transit pod” — an enclosed, golf cart-like vehicle that will hold one or two people.

Lime is positioning itself as an “affordable” alternative to traditional means of last-mile transportation — it claims that 34 percent of its riders report an annual income of less than $50,000. And it credits that affordability with its mobile app’s rise to the top of download charts in New Zealand, Czech Republic, Austria, Poland, France, Portugal, Greece, and Spain.

Its partnerships likely have something to do with it, too. In June, Uber said it would begin renting Lime’s scooters via its app, in addition to investing in the startup. And more recently, in December, Lime integrated with Google Maps in over 20 cities.

“Micromobility is growing at a faster rate than we have ever seen, but the industry is still in its early days,” Sun said. “As we move into this next phase of growth and adoption, Lime is committed to leading the way in collaborating with policymakers, the industry and local communities … I want to thank our investors, the entire Lime team and most of all, our riders for getting us to where we are today.”

Lime’s competitors are myriad, but its chief rival might be Bird, which has raised $400 million in venture capital for its electric scooter service. But Lime certainly seems to have a knack for fundraising — in the 18 months since its founding, it’s raised $867.1 million (according to PitchBook data), and its series C in June attracted $335 million.

That hasn’t shielded it and other so-called “micromobility” startups from regulatory scrutiny, however. San Francisco essentially shut down electric scooter programs and created a license application process. Toward that end, Sun today pledged to work with regulators — through data-sharing partnerships with cities like Austin and Kansas City, for example, and memberships on local task forces like the St. Louis Scooter Safety Task Force — to “[help] communities … elevate [last-mile mobility] in public policy development.”

“Over the past few months, Lime has led safety initiatives around the world,” he said. “From safety education campaigns to hundreds of thousands of free helmets to leading the industry in liability insurance and scooter innovation — every member of the Lime team is committed to getting it right on safety.”

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