Hamburg public transport (HVV) shows two variants on relations for subway/lightrail lines splitting into a "Y" (three endpoints):

  • S1 (Relation 1660624): starts in Wedel goes via Ohlsdorf and then either continues to end in Poppenbüttel or Airport(Flughafen).
  • U1 (Relation 1687370): starts in Norderstedt Mitte goes via Volksdorf and then either continues to end in Ohlstedt or Großhansdorf.

Maybe there is subtle differentiation here (which I don't see) on how these trains serve the alternative endpoints by splitting (front/back) at Ohlsdorf/Volksdorf or alternating full trains serving alterative routes (S1 splits in Ohlsdorf), but I would like to understand the reasoning behind mapping S1 as two fully parallel lines starting in Wedel (four relations) and U1 having one main line until Volksdorf plus two connecting lines (six relations).

Both variants show up very differently in Overpass (U1 S1). I would consider S1 Overpass the correct way to display such a Y-line. But I'm not sure if the difference in relation-style explains this and needs to be fixed.

asked 25 May, 07:59

Aeroid's gravatar image

Aeroid
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accept rate: 0%


The graphical representation with Overpass seems to be misleading. Have a look at these alternative graphs: S1, U1. You can switch on/off the individual branches through the menu under the "LS" button on the top right.

Both ways of mapping are used. I tend to follow the S1 way and I think that is what is mostly done in my local Verkehrsverbund but the U1 way is quicker to do as you don't have to repeat everything for the common section.

As long as we don't have timetable information in our data it doesn't really matter which way is followed.

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answered 25 May, 08:46

TZorn's gravatar image

TZorn
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accept rate: 16%

edited 25 May, 09:06

Thanks, but I guess the 6-relation-variant (U1) has the general disadvantage of not differentiating between the two "leaves" and the "trunk". That Overpass chooses the "joint" as a starting point out of the four options is certainly the worse case, which S1 avoids by not offering the "joint" as an end point.

(25 May, 10:16) Aeroid
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question asked: 25 May, 07:59

question was seen: 213 times

last updated: 25 May, 10:16

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