The dotted brown lines tends to be "track" roads as in they typically are of  very poor quality and seldom used.  Typically you will need at least a 4WD high clearance truck to pass these.  There is a grading for some of these that are arbitrarily assigned based on whoever mapped them, and some of the higher grades (lower number like grade 1) can be passed by some passenger cars.
Beware a lot of these are private roads and may not be legal for random people to pass.