From another discussion elsewhere :
Survey to obtain the 85th percentile on a road :
person 1 wrote:
BTW survey was carried out by an unmarked vehicle, my own car
Seems odd to use your own car is that - common practice ?
So what part of your job leads you to carry out surveys? Is this something that you do often ? Who takes your data?
Was your car sitting back off the road? Clearly labelled that you were doing a survey?
What is the proximity of vehicles to you when you note their speed and is that ahead of you or after they pass you? and when ahead of you what sort of distances?
What device do you use to register and verify their speeds? (please & thanks).
person 2 wrote:
... is there anything wrong with applying the highest common denominator of 85th% limit throughout that stretch, or even just NSL?
person 1 wrote:
nothing at all, only if every driver was a high level driver to IAM grade, ...
If the 85th% of drivers are travelling safely up to certain speeds, then we are already talking about them without further training, of course, so then, why should we be considering that only those with added training can 'drive at the 85th%ile ?
The 85th%ile is based on standard training, those with further training simple drive with more ability, knowledge & skill, (usually) with better safety margins and often driver slower than others too.
(To the people involved - if you wish to be ID'd let me know).
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