Guidance for length of placement=transition segments

At typical roadway merges and diverges, there are road segments where the driving direction is not parallel to the way itself, but there is a (small) angle in between. These segments can be tagged with placement=transition to indicate this (or, alternatively, placement:start=* and placement:end=* with different values). This is commonly useful for describing lane geometry at motorway-like junctions and transitions between single-carriageway and dual-carriageway sections.

However, I am wondering if some guidance on the desired length of the transition can be given, as this appears to be poorly documented and hence varying according to personal preference of whoever mapped a particular road:

  • The placement=transition wiki page suggests to match the length of the painted gore, with which I tend to agree except if the gore is very long.
  • @Allroads contacted me stating that he instead prefers to use short segments. His transitions are typically a couple of meters long at roughly 45 degrees.
  • The placement proposal shows examples with transitions of various lengths, including one extreme example where the transition segment is practically orthogonal to the driving direction to make it as short as possible.

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Ce sujet de discussion accompagne la publication sur https://community.openstreetmap.org/t/guidance-for-length-of-placement-transition-segments/108957