Google Maps bicycle option
google maps shows most every trail, from short ones in city parks to the longest ones.

Pull down the left side menu and select Bicycling.

You have to zoom in to at least the "10 mile" zoom level before the bike trails display.
Zoom way in on trail to see it's name repeated along the line, then you can google that trail name for more info.

For example, southern PA with the GAP trail heading SE from Pittsburgh.
https://www.google.com/maps/@40.2283.../data=!5m1!1e3

What are the solid or dotted lines?
The trail markings don't all have their previous meanings, and there's no info from google itself on the new markings.

previously,
solid green line: a paved trail
solid brown line: unpaved trail
dotted line: a bike lane on a road.

Now:
dashed green line: unpaved trail?
solid dark green line: might be paved or unpaved trail.. why! See the GAP trail around Ohiopyle, some of it is solid, some dashed, but it's all the same unpaved, crushed stone surface.
solid light green line: bike lane on a road
dotted line: bike friendly road. (some are more "friendly" than others, though.)
solid brown: unpaved trail or dirt path.
The current map legend. Doesn't show the dashed lines here.



Street View!
A few trails have Street View, from a bicycle towed camera.
zoom in, drag the yellow "street view guy" onto the map and see if the trail is included.
For example, the Little Miami Trail near Loveland OH: