[Talk-GB] Where do speed signs take effect (from Changing "stub" cycleways to pavements)

[Mark Goodge]

On 15/02/2022 06:55, Tom Crocker wrote:

> Hi DaveF, I'm intrigued. I thought the large speed sign did mark the 
> point of the change in legal speed limit, although of course approaching 
> the junction it wouldn't actually be safe to travel at that speed. I 
> remember the teacher on my speed awareness course (oops) making a 
> similar point and "Know your traffic signs" [1] seems to say this. Am I 
> missing something?

This is one of those situations where there is no single "right" answer, 
because, like a lot of legal matters, the law allows for a certain 
amount of pragmatic fuzziness in implementation.

Any deviation from the national default speed limit requires that the 
new limit is imposed by a Traffic Regulation Order (TRO). But a TRO is 
not in force unless indicated by signs. That is, both a TRO and signage 
are necessary conditions for an enforceable speed limit, but neither 
alone is sufficient. If there is a TRO but no signs, then the TRO has no 
effect. If there are signs but no TRO, then the signs have no effect.

In cases like the Hood Lane 20mph limit, it's normal for the TRO to be 
applied to the entire street - the actual wording will usually just name 
the street and its classification number. But the signs will be erected 
at a point where it is most convenient or appropriate to do so, which 
may not be right at the end of the street.

What that means in practice is that the enforceable speed limit - the 
stretch on which you could be ticketed for doing 25mph by a policeman 
with a speed camera - starts and finishes at the signs. But the TRO 
imposing the limit will cover the whole street. It just won't be in 
force at the stubs at each end.

How you map this is, therefore, a matter of interpretation. One option 
would be to map the limit as only being between the signs. If you were 
mapping a speed limit change on a continuous road - eg, where a road 
crosses the boundary of an urban area - then you would certainly map the 
change as being precisely where the signs are. But where the limit 
change is associated with a junction (as here, at Hood Lane), and it 
just so happens that the signs are set back slightly from the junction, 
then, in practical terms, it may well make more sense to map the limit 
as extending to the junction because that's more useful to consumers of 
the map. Even though that short stretch between the junction and the 
signs does not have an enforceable 20mph limit, the reality is that 
nobody is going to be going that fast anyway at that point and having a 
short stretch mapped as 30mph is liable to confuse things like sat-navs 
which include speed limits in their data.

So, in this particular case and others like it, I would tag the entire 
street as having a 20mph limit. That's not necessarily the most 
pedantically correct option, but it is the one which is most appropriate 
for the on-the-ground conditions. And, while OSM not in any way obliged 
to follow the conventions used by other mapping agencies, most of those 
which use speed limit data (eg, sat-nav map providers) would tag the 
entire street as having a 20mph limit here.

Mark