Turn:lanes=slight_left/right versus merge_to_left/right

A mapper in the region has been applying connectivity relations and turn:lanes tags onto motorway, trunk and primary roads in large numbers. Large numbers are also flagged by QA, particularly Osmose (just inhale and exhale slowly please). The central issue is in all of the flagged points is that AFA turn:lanes are concerned which are mapped to seemingly none existing lanes and or lanes are tagged as were they a continuance, my interpretation, opposed to a lane that ends.

Trying to understand the meaning of one not seen before in data is slight_left and slight_right flagged in every place seen where used here. In the instance a parallel ramp-on was changed from 2 + 1 lane ways with a joint to a single 3 lane road eventually changing to 2 lanes or for that matter 2 lane road changing to 1 (main plus ramp on).

The turn:lanes value given in the example is through|through|slight_left. Looking at the wiki on turn:lanes in past I would have given the merge_to_left instead (see pic below) of the Ortona motorway junction. Slight_left to me is just saying the lane you’re following is bending slightly to the left, not ending, where merge tells the lane you’re in is ending, move over to the left in places called in free translation ‘zip’ while adapting your speed to the lane you’re changing over to without causing slowing on the main route.

Notably there’s no direction arrows on the deck, only solid and dashed lining as dividers to indicate where changing allowed or not.

Comments please, slight_left or merge_to_left?

(I’ll write up a separate post on the many connectivity relations being flagged at junctions, not seen in the larger region until now)

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Ce sujet de discussion accompagne la publication sur https://community.openstreetmap.org/t/turn-lanes-slight-left-right-versus-merge-to-left-right/106841