I was under the impression that for minor roads which are maintained by either the County or City, a 30 foot ROW width was implied.   I do know of cases where there are only 20 foot record public roadway ROW widths (and alleys with a lesser dimension).

If the roadway and the maintained cut and fill slopes along with the roadway ditch sections are actually wider than a 30 foot ROW, then a 40 or 50 ROW might only make sense.  Who wants to be responsible for growth and vegetation along a steep roadway cut or fill.  Seems like a liability issue.