Adding bridges (keepright)

Keepright shows lots of missing bridges in northern NH. Three questions from a user new to armchair mapping:

  1. Is it safe to insert bridges in interstates and US highways? They involve relations, about which I know nothing, and I believe that “If you do not know what you are doing, don’t do it!!”.
  2. The NH-VT state line runs right down the middle of the Connecticut River, so the highway changes name and ownership right in the middle of the river. What is the correct way of making bridges which cross a state line?
  3. Finally, is there any genuine value in adding bridges? I am sure that routing software will happily route you over an unbridged river!
  1. It should be safe to insert bridges for both JOSM and Potlatch - both editors do the right thing: have the bridge in the same relation as the original highway. The only impact of the relation is that it extends the object being modified to the entire length - often through the entire state. So be sure to upload often enough if using JOSM to minimize possible edit conflicts.

  2. The highways will already meet in the middle of the river, so just split each one at the start of the bridge, and there will be 2 bridge segments.

  3. I think the biggest value is that bridges will be shown on a visual map. Routing software generally ignores bridges, except in one case I know of, OpenTripPlannner uses elevation data for bicycle route planning to avoid hills. When it sees a bridge over a ravine, it connects them with a straight line rather than following the ravine.