On a normal (right hand drive) road before a slip lane or highway exit the way would be tagged as through|through;slight_right assuming it has two lanes and the slip lane that comes off the right-most lane. My confusion comes in when the main road has a 30-ish-degree bend to the left, and the slip road has no bend. What do I do here? Do I tag the main road lanes as slight_left and the exit lane as through or do I tag the main road as through because it is the road that continues, and if that is the case, what would I tag the lane that has access to the exit road?
I would orientate myself on the markings. If the through-lane-markings are straight, even if the road takes a turn, I would mark it as through.
This way you give the routers the best possibility to represent the sitiuation on the ground, as a drivers assistance. And you spare yourself the question at which degree you change from ‘through’ to ‘slight_*’.
I agree with @Robert46798 : If there is a very clear “through” or main direction which doesn’t use bend arrows as marking, then this should be tagged as “through”. If the “main” direction is not very clear (e.g. as on a small urban intersection vs. a trunk road with a dedicated slip road) and significantly bend, then there is no problem in tagging this as “slight_*”. The tag is mainly meant to be displayed to the user.
You missunderstood me. This question arise, if you define the turn value according to street shape, rather than the arrows. (Which I do not recommend.)
I know the difference between an straight arrow and one which bends a little
Hi, I think that the wiki is pretty clear about this. You’re supposed to use the turn lanes tag for the indicated turns (by arrows on the ground or on signs). Where this is insufficient, a connectivity relation might be useful.