In the present study, we quantify and validate global accessibility to high-density urban centres at a resolution of 1×1 kilometre for 2015, as measured by travel time. The last global mapping effort to measure accessibility was for the year 2000, a time that predates both substantial investment and expansion of transportation infrastructure and an extraordinary improvement in the data quantity and quality of accessibility measures. The game-changing improvement underpinning this work is the first-ever, global-scale synthesis of two leading roads datasets – #OpenStreetMap (OSM) data and #distance-to-roads data derived from the #Google_roads database – which resulted in a nearly five-fold increase in the mapped road area relative to that used to produce the circa 2000 map. A major strength of the new roads data is its inclusion of minor roads (e.g., unpaved rural roads), which comprise a large proportion of roads in many low-resource settings and were largely absent or geographically inaccurate in previous roads databases. As such, the improvements in our accessibility map are most prominent in the areas where quality data are most needed for informing sustainable development policies and actions. To illustrate the far-reaching utility of our 2015 global accessibility map, we conduct exploratory analyses that enumerate geographic and wealth-based inequities in accessibility. We also show that shorter travel times to population centres in low- to middle-income countries is strongly associated with socioeconomic and health indicators (i.e., household wealth, educational attainment, and healthcare utilization), highlighting the vital role of accessibility in the pursuit of sustainable development worldwide. Beyond the socioeconomic and health domains, this work could be used to inform environmental and conservation efforts to balance infrastructure demands with ecosystem preservation.