Going to do Joburg central from Pretoria central and back is about 110km. Thats 2200km in a standard 20 work day month for a commuter. Lets say cars average at using 9l/100km, that means 198l a month. So the average for a person driving currently to JHB CBD and back is around R1590pm if the petrol price is R8.
Now that is just the petrol and excludes the service ( approx R500 to R2000) cost for every 10 000km to 15000km (13800km used in 6 months driving if using my average or 26400km a year) and the proposed 50c/km toll road fee with would be around R60 a day (1200pm) assuming 60km of the road is tolled.
So the possible expenditure is around R2800pm (at a R8 petrol price, which will likely just go up more from now) just to drive to JHB central from PTA central and back every work day on a month. How does that compare to say a monthly R800 gautrain ticket?
Then what do you do when you arrive in Sandton? It's not like you can walk to your meeting/office or whatver or catch a tube train closer to your destination or ride on a reliable bus service...