They hide their car in a ditch on the northern side of the N10 bridge over the N1, and the camera is on the bridge above on the N 10. No one sees them. And yes it is a 80 zone and after that long stretch from Richmond, you have to be very vigilant otherwise you will miss the sign.
Very familiar with that part of the N1 and N10, it is where we turn off on the Bokfontein dirt road, to our overnight stop at a cousin's place, one of the worst dirt roads you can imagine.
Also the road to a farm called "driekoppen" where the current owner has one of the most impressive pubs full of Springbok memorabilia you can imagine.
Warning - if the old flag upsets you stay away from that pub -