Sidewalk Labs, a secretive subsidiary of Alphabet, wants to radically overhaul public parking and transportation in American cities, emails and documents obtained by the Guardian reveal.

Its high-tech services, which it calls "new superpowers to extend access and mobility", could make it easier to drive and park in cities and create hybrid public/private transit options that rely heavily on ride-share services such as Uber. But they might also gut traditional bus services and require cities to invest heavily in Google's own technologies, experts fear.

Sidewalk is initially offering its cloud software, called Flow, to Columbus, Ohio, the winner of a recent $50m Smart City Challenge organized by the US Department of Transportation.

Using public records laws, the Guardian obtained dozens of emails and documents submitted to Challenge cities by Sidewalk Labs, detailing many technologies and proposals that have not previously been made public.