adjustable matching threshold for segments
One long-time limitation of the segment matching algorithm has been the ability to define segments in route-rich environments in which alternate routes may match and start or endpoint and cause a false hit on a segment. One such example is this one:
Quane has a substantially distinct character from the parallel street, Dolores, and it would be possible to separate efforts from the two streets, yet the matching threshold on the start and end points is too loose to filter the two, so the segment instead becomes basically a segment for the climb on either road (at least the eastern side of Dolores).
The tradeoff is obvious: you typically want a runner to be able to match a segment on either side of a broad street, or to have a chance to match a segment in the presence of systematic position displacement. However, on short segments not one is position integrity more important (time differences are small so position errors have a greater effect), but in urban contexts it becomes impossible to isolate some interesting routes.
The solution is to allow for a "threshold", similar to the privacy threshold, to be set on the start and/or end points of a segment. This could be tightened or loosened depending on the surrounding environment and/or the length of the segment. For example, a segment for a 100 km segment of the coastal highway would be set loosely, while a short but interesting climb would be set tighter.
This need not be mandatory, but instead provided as an option in the segment definition/editing page. The GUI could be kept relatively clean. And it would serve to go a long way toward cleaning up the leaderboards on many running segments in San Francisco.