User:Zverik/Main Road Research

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So, the discussion with Harald from Skobbler has given us three major points for good routing applications with lanes:

  1. Turn Lanes tagging scheme (being voted on right now)
  2. Destination signs (already present, but not popular)
  3. Tagging scheme for main roads / through direction.

On this page I research the latter. In English, because it could be discussed with mappers from other countries.

The Task

There are several key points, for which we need tagging scheme(s):

  1. There is a sign, "main road". It currently has no representation in OSM data.
    8.13 (Road sign).gif
  2. Sometimes a road does a slight turn, while a secondary road goes at such angle, that it can be considered "forward" direction by a program, although it's a right turn for a human. In this case a program should shut up.
  3. On complex crossings, or when angles are all askew, a program cannot determine if the route goes through, or if it's a turn. Routing can depend on a number of left turns and such.
  4. To apply the turn lanes tagging scheme, one must know which way is "forward", and which are turns.
  5. And don't forget two-way roads.

Immediate Problems

This intersection. Clearly the main road goes slightly left, and the way forward is as wide. If a software will keep silent, a driver could forget to keep left and miss the main road. Possible solution: "stay on the main road", something like that. Is it better than "turn left"?

In such situation a clear instruction is needed, something like "Stay on the left lanes and follow further the XXX". --Imagic 15:47, 19 January 2012 (UTC)

Main Road Relation

A relation with two or more connected ways, with type=main_road. Probably with optional straight=yes/no. This automatically eliminates two ways from a crossing while searching for "through" way, and helps determining how much time would the crossing take (a lot less when driving the main road, naturally).


There are 24 main_road=yes tags, used in relation type=right_of_way. There is a proposal, probably the same as main_road relation proposed above (todo: read it). There are 52 relations of that type in total (which means only half of them have main_road tag). An extract from Overpass API.

No type tags with "main" inside values.