Unsurprisingly, roads are designed and built with certain speeds in mind, and - excluding national speed limit country roads - this broadly means that the wider the road the faster you’re able to go safely.
It's been really driven home (sorry, no pun intended) by me looking after my brother's house which is on a very long wide, pretty straight road with lots of off-street parking. It and another similar road running at 90 degrees are key connecting roads that form a rectangular box for the area but two are 30mph and two are 20 with no rhyme and reason for it (one of the 30s has a much narrower stretch).