[Talk-GB] Where does a motorway start?

[Mark Goodge]

On 03/08/2022 11:15, SK53 wrote:
> I have a vague feeling that when I hitchhiker (about 40 years ago, 
> initially because of a rail strike) the lore was that you were OK if you 
> stood in front of the sign. Certainly the police were more tolerant if 
> one did so. This is practically the only use case I can think of which 
> such mapping might support. Mateusz' suggestion of mapping the sign 
> would also provide the necessary information.
> 
> I think these should be reverted, as it may create a precedent for 
> similar edits for 20 mph limits on residential roads, where most signage 
> is also set back from the junction. The current style of mapping has a 
> huge weight of precedence & implicit consensus behind it, not just in 
> the UK, but worldwide.

Both of these are examples of a subtle, but nonetheless important, 
distinction between the designated status of a road and the position at 
which the regulations relevant to that status become enforceable.

Signage, for practical reasons, can't always be placed at the exact 
point that the status of a road (eg, the classification, or the speed 
limit) changes. But the law does not expect people who are using the 
road to refer to a map to know which regulations apply at any given 
point. Rather, they are expected to obey the signs. So the regulations 
applying to the underlying status aren't enforceable until the position 
of the sign.

As far as mapping is concerned, the convention - not just in OSM but 
every other mapping agency as well - is to map the underlying legal 
status of the road rather than the enforceable status. That's the only 
practical approach, given that signs can, and sometimes do, disappear. 
If a speed limit sign is knocked over by a vehicle, the underlying 
regulations applicable to the road don't change. But, until the sign is 
replaced, the limit becomes unenforceable. If a street with double 
yellow lines is resurfaced, then the lines will disappear until 
replaced. That doesn't change the Traffic Regulation Order applicable to 
the road. But it does mean that until the lines are re-painted, the TRO 
can't be enforced. And so on. But the enforceability of regulations 
isn't directly relevant to mapping, unless mapped in addition to (rather 
than instead of) the underlying status.

Mark