Where Google Maps gets speed limit data?

Inspiration

I was driving I passed a strip of road that had no speed limit sign, yet Google Maps said “60 MPH” going in both directions. I wanted to know where it got that data if it wasn’t scraping it from Street View photos.

My guess before digging in

That there are government databases that Google can pay to have access to, if they’re not available to the public already as a result of tax payers’ money

Findings

• I haven’t found anything concrete, yet. There are just people guessing, others say Street View imaging, but that doesn’t address my scenario. Other people say from local governments. These are all guesses though.
• This Google Blog post explains a lot of the ways they do this
  • As far as data sources from local governments, it seems to be the basic “25 MPH in residential areas”
  • They parse the images from Street View
  • They use traffic data to see if cars are consistently traveling below the speed limit as that could indicate a change in speed limit
    • If they suspect a change, they cross-reference it with multiple sources like data from local governments and refreshed Street View imagery
    • If they don’t have recent Street View imagery available, they request images of the specific stretch from third-party partners

Follow-up questions

But how did Google Maps decide to say that road had a 60 MPH speed limit?

• Still no answer unless the “local government” told Google and just chose not to put a speed limit sign up