[Ready] Be more aggressive classifying Roundabout Intersections

[daniel-j-h]

Roundabout Intersections are roundabouts with up to four ways and turn
angles which makes the turns obvious, e.g. as in:

    *
    *
* *   * *
    *
    *

but not e.g.

     *
    *
* *   *
    * *
     * *

For Roundabout Intersections we issue instructions such as
"turn " instead of "take the exit".

At the moment we have a limit on the radius for these Roundabout
Intersections of 5 meters. Which fails to classify a wide range of
Roundabout Intersections in the US (with the US-wide streets).

Example: http://www.openstreetmap.org/way/348812150

This changeset removes the Roundabout Intersection radius limit:

• if the roundabout is larger than a threshold and is named we classify
  it as a rotary
• if the roundabout matches our criteria for Roundabout Intersections
  we classify it as a Roundabout Intersection (note: we no longer care
  about its radius here)
• else fall back to plain old Roundabout

Up for discussion. cc @1ec5 @MoKob @TheMarex

There is a second issue with determining a roundabout's radius.
But that's for another pull request (tracking in #2716).

[daniel-j-h]

This scenario is new, the other ones are adapted to Roundabout Intersections.

[1ec5]

That sounds reasonable for the case given above, which is essentially just a traffic calming device. Do you recall how the five-meter threshold was determined? Are there counterexamples in Europe where a ten-meter-wide roundabout would be a conventional junction rather than a traffic-calming device?

[daniel-j-h]

I don't recall the 5 meters heuristic --- could be totally guestimated.
We have to wait for @MoKob for insight here.

My main point is: once we have determined it's not a rotary (large named roundabout), does the size actually matter for classifying these as roundabout intersections?

As long as the roundabout intersection criteria are met, I see no reason (other than maybe mis-tagged rotaries?) to not announce them as turns.

[emiltin]

i agree that it makes sense to announce turns if it's not a rotary and the turns are almost 90 degree. for example this series of roundabouts:
http://www.openstreetmap.org/#map=16/55.6564/12.5864

in additional to turns being almost 90 degree, there clearly a main road continuing straight ahead, which makes "straight ahead" even more natural.

[MoKob]

if we want to have it classify as a turn, this should not only be adjusted but moved to the intersection features.

[daniel-j-h]

Adopted code to comments: added upper limit for roundabout intersections, moved the cucumber tests into the roundabout turns file, created roundabout turn bike test. Rebased against master. Waiting for Travis, then ready to go.