Chris Barrington-Leigh and I have been working for the past few years to assess the completeness of the street network in OSM. We're pleased to have now published our results in the journal PLoS ONE. Thanks to many suggestions from the OSM community on our preliminary analysis.
Here are the highlights from the paper's abstract:
We find (i) that globally, OSM is ∼83% complete [as of January 2016], and more than 40% of countries—including several in the developing world—have a fully mapped street network; (ii) that well-governed countries with good Internet access tend to be more complete, and that completeness has a U-shaped relationship with population density—both sparsely populated areas and dense cities are the best mapped; and (iii) that existing global datasets used by the World Bank undercount roads by more than 30%.
An update using the April 2017 snapshot suggests that completeness is now ~89%. Our more detailed results and all our code are available on GitHub. Here's a sample of the largest 10 countries (updated through 2017), showing the actual growth in OSM road length and our model fits:
And here's the fraction complete, also updated through April 2017: