Author mentioned OSM but they could also use Mapbox's navigation APIs if they don't want to host things themselves.
OpenStreetMap itself is just the base map, not a provider of traffic data or routing.
I still think location data collection for the public good should be run by someone who is not Google / Facebook / some other company that doesn't already track everything about you. I'd be happy to send my real-time location to a company like Mozilla or some mapping company (just in the tiny netherlands I know of AND, Geodan, OsmAnd... I'd be fine if any of them organize this).
We also have some open data via the government, based on detection loops in the road, but if I remember correctly it's only (or mainly) on highways.
I still can't believe Google does not have a GUI to both style a map AND add markers to it, but they have GUI for those things separately.