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When Polish road authorities refer to a location along a road using kilometric points, they append an extra letter (S5a, S5b, S5c…) to the road number to refer to different stretches of the road with different zero points.

For example, on the S8 numbering restarts at 0 behind Zambrów-Wschód and counts upwards until just before Jeżewo (at approx. km 29.6), where the numbering continues with km 615.4. That stretch is referred to as S8n.

This is especially common on expressways, which are often former national roads, upgraded to expressway standards and rerouted around built-up areas. Often these bypasses got built first and numbering would restart at km 0. Some roads have as many as 16 different points marked as km 0, and in some places numbering restarts at zero after as little as 10 km, thus disambiguation is paramount.

Sometimes the road number with the extra letter is reported on the delineators (which also serve as location markers); the S8n is such a case. On other stretches of road, the road number is indicated without the letter (i.e. S8) and thus cannot be gathered by means of ground survey (or OpenStreetCam, Mapillary and friends).

Does anyone know where a list of these “extended” road numbers (with information on the stretch of road they refer to) can be obtained, under an ODBL-compatible license?

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The Polish Open Data portal (https://dane.gov.pl) has several data sets from which this information could be derived.

Filtering for data sets provided by GDDKiA (the national road administration), there are several data sets:

  • Highway service areas (Informacja o Miejscach Obsługi Podróżnych)
  • Charging stations (Plan lokalizacji ogólnodostępnych stacji ładowania), though most of them are part of service areas
  • Traffic cameras (Lokalizacja kamer monitorujących przy drogach krajowych)
  • Current traffic disruptions (Utrudnienia na drogach)

All report road numbers with the extra letter (when used without an extra letter, kilometric points are relative to the original course of the road). However, they are far from covering the entire road network: if a stretch of road has no rest areas, charging stations or traffic cams, you may have to spend a long time following traffic reports to learn about of its existence (and even then, there may not be any traffic disruptions affecting that particular stretch).

As per § 5 of the terms of the portal, all data is free for use without restrictions unless an individual data set indicates otherwise, and the descriptions for these sets do not specify any other terms.

Some local GDDKiA offices maintain a list of the roads under their responsibility (with the section identifiers) and make it available on the GDDKiA website, though these are likely not open data. However, dane.gov.pl accepts suggestions for further data sets and investigates if they can be provided as open data; I have suggested opening these up.

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