Creating a sidewalk map for a walkability survey

If I wanted to do my own walkability survey of my city, what tools could I use? I have map data from OpenStreetMap, but I have to consider that streets have two sides (which aren’t always accessible from the other side of the street). I guess I need to make a sidewalk map.

I’d like to use path-finding algorithms against the data to provide walking directions that avoid sections of streets with poor walkability. Some blocks have sidewalks, some don’t, and some streets have a sidewalk on one side but are too busy to cross. The directions would cross the highway at places where it’s easier–very easy at the crosswalk, hard at several other streets, impossible at a few streets.

I know that weighted path-finding algorithms exist. I’m just wondering how to create this data. I’ve toyed with taking a map image, putting it in Inkscape, turning on grid lines, and overlaying paths along the sidewalks. With the grid lines, the points of paths connect for path-finding. Path color indicates difficulty of walking. Aside from the path-finding, it’d be a good map to show walkability in town.

Anyone have any ideas?