KCBS_740SAN FRANCISCO (KCBS) — 45,000 Uber and Lyft drivers are registered to drive the streets of San Francisco.

The new numbers from the San Francisco Treasurer’s Office even surprise experts.

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The number of drivers has risen from 45,000 from an estimated 37,000 in April. That dwarfs the 1,800 taxis on city streets. Given how hard it is to maneuver around the city, what’s causing this growth spurt? Is it late-comers just discovering the ride hailing economy? Are they people trying to make a living picking up condo owners in all the new glass residential high rises?

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SF’s Municipal Transportation Agency wants to know, but it hasn’t heard back on requests for data from ride hailing companies, according to the Examiner.

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Critics like taxi companies blame congestion on Uber and Lyft, while academics that study transportation say that’s not yet a fair assessment, because all 45,000 ride hailing drivers are not on the street at the same time.