It’s easier said than done to avoid the N1, as the alternative routes are notorious for being poorly maintained and potholed.
Considering the options with my travelling companions – a mother and her two young adult daughters – we opt to leave the N1 just after Vanderbijlpark and take the R59 to detour through the Vredefort Dome, aka Vredefort Crater. It’s an attractive waypoint and the roads are usually passable.