*** Simple tools like that are always a great help for initial layout.
Perhaps the better description of those widths may be "Driveway and B road" in the real world though.
In Roman times, 18 feet or so was the norm - 72mm, close to Simons figure
In Tudor times as land became enclosed for the first time, roads built at land boundaries were perhaps 70~100mm wide in 4mm scale, and we often much wider.
In the 1700's a similar width was used for miliraty roads.
Once traffic increased, significantly more width was used to allow regular two-way traffic.
This link is a start for researching the subject.
https://www.sabre-roads.org.uk/wiki/index.p...tle=Road_Widths
However.... Model railways do not have too much space. Sometimes a wee bit of conpression may be helpful, and we should remember that the road width can include shoulders and other space betwen boundaries too.
Simons road width will therefore be a useful compromise in many cases as long as its used as the hard surface width, not the "between fences" spacing.
regards, Richard