In this scenario, you can base your calculations on the 3-second rule.

The 3-second rule states that you should keep at least a '3-second distance' between your car and the car in front of you. When driving at 70 km/h, you are travelling about 20 metres per second – or 60 metres in 3 seconds. The distance to the car in front should therefore be at least 60 metres.

Note that in general, when you are driving at speeds above 80 km/h, the distance to the car in front should always be more than 3 seconds.