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Braking distance and following distance are two distinct things.

Following distance is the rule that you should leave a 2 second gap in front of you. That is often less distance than the braking distance.

You should be always able to see that your braking distance is or will be clear, and that sets the maximum speed you should drive at as you approach areas with reduced visibility, like corners or the brow of a hill. You must learn braking distances for the driving test.