There are far more limits to procedural lanes generation than in carriageways. This is because lane have a much more local variability nature than carriageways. For example:
In other words, lanes vary across the same road much more than carriageways. Creating really useful lanes (especially merging lanes etc) requires more detailed width calculation (e.g. a width per segment of the same road) which are also more prone to errors.
There are far more limits to procedural lanes generation than in carriageways. This is because lane have a much more local variability nature than carriageways. For example:
In other words, lanes vary across the same road much more than carriageways. Creating really useful lanes (especially merging lanes etc) requires more detailed width calculation (e.g. a width per segment of the same road) which are also more prone to errors.