When i did my national standards Cycle Instructors course one of my first questions was do drivers know about this and if not why not? The answer, "It costs too much to advertise"
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I would love to see a public information campaign aimed at all road users explaining cyclists road positioning and rights.
The OP raised some interesting points and was a good, frank and thought-provoking piece.
This lack of wider awareness raised by AFsolo is critical.
There was a tired, old joke about Belgium changing its traffic laws and adopting the UK system of driving on the left. They decided to stagger it ; trucks and buses one day... cars the next.
If cyclists are adopting a road-position stance of which many other road users are unaware, there is a problem.
To a driver unaware of the concept of 'primary', a cyclist riding there may appear to be riding dangerously, selfishly or similar.
Most drivers are unaware of the concept of bicycles adopting primary position in certain circumstances. I think we are all agreed on that.
Many drivers are not cyclists and are quite unaware of the needs of cyclists (this is not a crime, any more than it is a crime not to drive and to be unaware of the needs of drivers).
It doesn't help that a minority of cyclists either misunderstand the circumstances in which the adopting of primary position may be appropriate or are simply spatially unaware. This is not a troll comment; I refer only to a small minority. We have all seen them.
The broader concept of adopting primary road position where appropriate is far from barmy. There is much to commend it.
Doing so among a wider motoring and cycling public who take their road use seriously (but are completely bamboozled by a cyclist moving into the middle of the road for what might appear to be a quite arbitrary reason) needs careful thought.
Many car drivers bumbling along a single carriageway at 30 might be unsettled to see a cyclist, doing 15 ahead of them, moving to primary as they approach a parked car on the right side of the road. The cyclist can argue that he is adopting primary to prevent a close pass. That may or may not be so. To the driver it may appear otherwise. It is often a good idea to think how our actions appear to other road users. Adopting primary can sometimes appear to some drivers like a red rag being waved. There is no training; there is no wider publicising of the concept; as the OP says, even the Police are not routinely told about it.
The great majority of drivers I've shared the roads with are courteous, skilled and aware of their surroundings. Many cyclists also appear to be.
When using primary in what can appear a fairly hostile traffic environment, it may be helpful to ask oneself what it looks like to the other road users who will need to adjust their speed or direction to accommodate our actions.
There is a danger that the use of primary position by UK cyclists will start to resemble the Belgian-joke scenario.
Thanks again to the OP for highlighting a most interesting topic.