Why go
A highway route gets you to Johannesburg, but it does not resolve the journey across it. Midrand and Soweto, for example, are more than 45 km apart. Using the exact destination when planning arrival makes more sense than treating the city centre as a proxy for every neighbourhood.
The full story
The N1 is a major approach from Cape Town and Bloemfontein, the N3 approaches from Durban, and the N12 serves the approach from Kimberley and Potchefstroom. Use these road numbers to orient the long-distance leg, then plan the connection to the address where you actually intend to stop. Johannesburg’s spread matters when deciding what to add to an arrival day. A destination on another side of the city can require a substantial onward drive even after you have reached the urban area. Check the distance between the accommodation and any planned visit before committing to both. For a weekday arrival, allow flexibility for traffic rather than building the plan around a single driving-time estimate. Check conditions close to departure and leave space before a timed commitment, especially when the route continues across the city.