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

[Chris Hodges]

I think you're right. Fiddling about with the grey-area speed limits of 
stubs just seems like clutter. The original question is more worth 
getting precise in that "can you go there?" matters more than "how fast 
can you go there?"


I wouldn't pay too much attention to what other maps/sat-navs do with 
speed limits, though. They're so often wrong even when the limits have 
changed in decades, and even when they appear to have precisely located 
themselves - and for most junctions the uncertain zone is within GPS 
location error margins anyway. I don't drive much but happen to have 
spent quite  bit of Sunday driving round the Brecons with Google 
navigation and this was one of several frustrations.

Chris


On 15/02/2022 10:02, Mark Goodge wrote:
>
>
> 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
>
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