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?