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Why lanes and lane_markings matter a lot

Posted Thu Dec 28 11:33:39 2023 Florian Lohoff
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I am currently extending my RouteQA slowly around Northrhine-Westfalia in Germany. I now extend to areas where mappers extensively mapped lanes=1 instead of lane_markings=no which breaks routing in a lot of subtle little ways at least for OSRM.

lanes=1 means it is not possible for two way traffic to pass each other without going to the curbs or shoulder. This causes the default OSRM car profile to assume half the average speed of the maxspeed.

So a road with maxspeed=50 and lanes=1 without any oneway tagging is assumed to have a max average speed of no more than 25km/h. Thats a pretty good assumption if its really too narrow.

Now if you have a tertiary or better road in city limits with a maxspeed of 50, and a parallel road with 30km/h the smaller side roads suddenly is faster because 30km/h is better than 25km/h.

So please stop tagging lanes=1 for roads which are wide enough for passing traffic without getting into each others way. The correct tag is lane_markings=no

In the default OSRM profile lane_markings=no has no penalty at all which IMO also needs fixing which why i opened an issue for the OSRM backend

Nevertheless - be careful with lanes=1 - its a hefty penalty for routing.

This is an example of broken routing in Borken near the Dutch border from my QGis view on the RouteQA.

As one can see the Butenwall is used but also the parallel Wallstra├če. The Wallstra├če would be used in ALL cases if it would not be a oneway.

The Butenwall as a secondary should be MUCH better - but it (was) tagged with lanes=1 as there are no lane markings. As a secondary it is wide even for trucks to pass each other without issues.