jondrush wrote:Nearly every ramp diverges at one or both ends. So a two-way joined to 2 one-way is three segments. Two one-ways from start to finish is two segments...
That is true. And when they diverge at both ends, as in the example that I posted earlier
, there are six segments whether you use one-ways or two-ways. So you are correct that using two-way ramps sometimes results in one additional segment. (The only time it reduces the count by one is when you have a single two-way segment, which is rare.)
reduced is the total length of roadway on the map: replacing two very close, parallel stretches of road with one. That means one segment to adjust to get the geometry right instead of two; one segment for a sometimes flaky GPS to snap to instead of two.
Plus you've taken away all sorts of decisions and penalties that the routing engine has to apply.
Such as? Two-way segments maintain independent speeds for each direction, and as I understand it, junctions keep track of the cost of each segment transition separately.
That is the crux of the difference between ramps and roads. Ramps almost always diverge. I've done lots of ramps each way. Editing is so much simpler without two-way ramps. I don't need to address 'symptoms', they just flat-out work, with virtually no URs.
And I find the map a lot simpler to follow and easier to maintain, in some cases, with two-way ramps.
Why are we even debating this?
1) The guidelines (rightly) leave room for a certain amount of discretion on the part of the editor;
2) The AM primarily responsible for this area for the past couple years sometimes finds it preferable to do it this way; and
3) It has solved URs and MPs.