Dogtrousers
Lefty tighty. Get it righty.
Not if the legislation is updated to change the national speed limit for such minor roads, it won't.
At present national speed limits are: M-way & dual carriageway 70; Single carriageway 60; Built up areas with streetlights 30.
So what is being proposed is (I think) is adding an extra clause to that: Minor single carriageway: 30.
That could work but it would need a simple, watertight definition of minor single carriageway that doesn't have any/many exceptions.
It would seem that "less than 5.5 m in width" would be the ideal one because the government traffic signs manual (2.2.6) recommends not painting centre lines on these roads, and it does recommend them on wider ones (table 2-1). So an alternative way of stating this would be equivalent to saying "single carriageway with no centre line marking", provided that the traffic signs manual is universally applied.
It would still require a major publicity/education campaign and possibly also explicit signs in some cases so it still wouldn't be cheap. Would it be beneficial? Maybe, but I'm not convinced.
At least I now have an idea what it's all about. Something that the wording of the petition doesn't give.