Author: tom[at]compton.nu
[Added to the original trac issue at 12.53pm, Monday, 7th July 2008]

Punting to Steve, but this would be horribly expensive to do so probably won't happen until mapnik is better able to handle it.

Author: philippep62[at]gmail.com
[Added to the original trac issue at 1.37pm, Monday, 7th July 2008]

It seems just a question on adding a (few) new rule(s) with some 'And lanes=' in it.
(I did try it on the style editor on osm.nl but it did not work , it reacted as there was no 'lanes' tag at all ...)
Kosmos do this easily ...

Author: tom[at]compton.nu
[Added to the original trac issue at 2.26pm, Monday, 7th July 2008]

I think you need to reconsider the value of "few" in that statement. There are many, many rules for rendering roads (probably a hundred or more) each of which would need to be duplicated several times. That is not something which scales sensibly.

There are seven basic roads types I think, each of which has three basic rules (core, casing and text) which gives us 21 rules. Those 21 rules are then repeated several times for different zoom levels (not all 21 rules will appear at lower zooms) in addition to which there are extra versions for bridge, tunnels, etc... Basically there is a combinatoric growth that is already out of control without adding extra dimensions of variation to the pot.

Author: math1985
[Added to the original trac issue at 10.31pm, Monday, 26th May 2014]

I think the width of roads should express the importance of the road, not the number of lanes. Some single lane roads can be very important. I therefore don't think we should implement this, and will close this issue as wontfix.

If you disagree, feel free to reopen the issue on the new issue tracker on https://github.com/gravitystorm/openstreetmap-carto/.