Trailforks for road bikes?
Google maps will show you paved trials open to bicycles and roads with dedicated bike lanes.

If you are a Strava user, you can use the route creation tool with heatmap turned on. That highlights bicycle trails very effectively.

Ride with GPS has a bicycle trails overlay in its route planner.

Really, any significant paved bicycle trails in a given location will be easy to find with a simple Google search, for instance searching for 'paved bicycle paths washington dc' turns up all the major paths in the area.