This is a quite old issue - see [#103][1] for discussion on the issue tracker.
As usually, the problem waits for somebody to make a pull request that will solve the issue. From looking at [#103][2] nobody tried doing it so far.
Unfortunately, this issue is not easy to fix so I would not recommend it as a task for somebody who never tried improving map style unlike some issues listed [here][3] (BTW, feedback from new and potential contributors is welcomed at [#2291][4] ).
[1]: https://github.com/gravitystorm/openstreetmap-carto/issues/103
[2]: https://github.com/gravitystorm/openstreetmap-carto/issues/103
[3]: https://github.com/gravitystorm/openstreetmap-carto/issues?q=is%3Aopen+is%3Aissue+label%3Aeasy
[4]: https://github.com/gravitystorm/openstreetmap-carto/issues/2291