Just as a foot note....a quick look at the VIC roads "wipe off 5" campaign gives an indication on how contrived "official" data can be.
Working backwards from their stopping distance table, they claim it takes around 1.5 seconds for a driver to "react" to a road event.
What a load of old cobblers! If humans normally reacted to events with this sort of brain dead delay, many activities would be physically impossible...eg tennis, cricket, football, ping pong..... forget it....the ball has always passed you by.
Yet the mantra is still chanted....even 5km/hr over is "dangerous"
Well, I suppose it is, if you are vision impaired, in a model-T with suspect brakes.
The key is anticipation, reading the traffic & being predictable. Time spent staring at the speedo is time lost looking for an unexpected event.