It's just not safe to race around at night anymore.
Eight West Rand drag racers have been filmed by a speed camera deliberately placed to catch them.

"We would normally have raided the scene with 100 police officers, but we wanted to get the evidence on camera. So we snuck in to the drag race and quietly set up the cameras to catch them," said chief superintendent Wayne Minnaar.

"Eight speedsters were caught travelling between 152km/h and 186km/h in a 90km/h zone."
full story from News24 here
I suppose 100 police officers is a bit light to wander around Johannesburg at night nowadays. Best to send out the robots.