FWIW, where I live the speed limit for what you are calling semi-trailers and road trains are the same. And I associate “road train” with Australia where there apparently can be quite a few trailers or semi-trailers being pulled by one tractor unit. Where I am the limit is two trailer/semi-trailers.
The UK English for semi-trailer is articulated lorry. Your road train picture would be described as an HGV with a trailer.
I don’t think I have seen any speed limit sign for anything more specific than HGVs, and I’m not sure that I’ve even seen that. Most absolute HGV restrictions are pitched only in terms of mass, although you get “unsuitable for HGVs” signs. There are national limits, but signposting the different values for different types of vehicle would just be confusing.
UK driving licences don’t distinguish between your two trailer cases.
Medium is determined by maximum authorised mass, not by whether there is a trailer. A vehicle in your first category that is over 7.5T MAM, is still a heavy good vehicle.
I suppose you may get more specific signs during high winds, but they are not mappable.
Your post says “This yet differs from a … road train”, yet your picture does not show a road train (by any British English definition). Road trains aren’t legal in the UK, though of course they are in some other places elsewhere.
We can leave out the road train for now, because I also have not found any legislation yet that sets different rules for these than for other vehicles with trailers.
hadw, the UK legislation does make a difference between HGV and articulated HGV according to this source: https://www.gov.uk/speed-limits (search for “if articulated or towing a trailer”). Independent of any signs, it should be possible to tag it somehow
n76: I would rather not introduce more sub-spaces in the key, it may become a mess and/or conflict in one way or another with the already existing sub-spaces forward/backward, conditional etc. Plus, I don’t think this kind of tagging is established in any way. For example, we do not tag maxspeed:psv:bus=50 (a bus that is more specifically a psv), but the vehicle class itself is expected to already be in a certain category (bus is a psv).
I thought a bit more about the name and discarded the following candidates (inspired by wiki article and replies here):
semi - semi-what? Too unclear
semi-trailer_truck, semi_truck - we don’t use the word “truck” for other trucks/lorries neither, using it here would be confusing
articulated_lorry - we don’t use the word “lorry” for other trucks/lorries neither, using it here would be confusing
I think there are two viable options:
hgv_articulated - oriented at the British-English “articulated lorry”
hgv_semi-trailer - oriented at the US-English(?) “semi-trailer truck”
Since OSM uses rather British-English than American-English and with regards to that it might be necessary to add another vehicle category later if law in certain countries differenciates it, namely bus_articulated, I suggested hgv_articulated.
If there are no concerns about this, I would go ahead and document it in the wiki.
I thought the general policy was not to interpret national speed limits in the tagging, unless there was an explicit sign with a numerical limit. I think HGV drivers are expected to know default limits much better than car drivers.
The problem is that, if you resolve national speed limit to actual numerical values, especially for specialist cases, and the legislation chagnes, it could take decades for the map to catch up.
In the UK, standard HGV speed limits are not generally signed, only the fact that the road is a motorway, or subject to national speed limits for ordinary roads or dual carriageways. In that case you should tag as national speed limit not as, say 60 mph, as the law could change. If the law changes this will be a maintenance edit and people much more like adding new things to the map, so it is likely to take many years before all the speed limits are updated to reflect the new legislation.
Data consumers should know the default limits for vehicle types, and apply them when they apply.
Its aim is to provide the concrete speed limits based on what has been tagged as the implicit speed limit (i.e. maxspeed:type=nsl_dual). With such a comprehensive list, it will be easier for data consumers to actually implement understanding this kind of tagging at all because honestly, I think not one router out there actually understands this tagging.
Also, I am hoping to increase acceptance by mappers for this kind of implicit speed limit tagging this way, because it shows that the actual speed limits are a bit more complicated than just glueing maxspeed=60 mph onto national roads. Doing that when no sign is around is actually technically adding wrong/incomplete information, as the page shows.
Lastly, with this page, I am trying to find out which maxspeed:type values for the different are actually needed, as well as, of course, vehicle types. For example, I and thus the German community only noticed during writing down the rules for implicit speed limits in Germany, that actually in Germany it is not only DE:rural but instead there is also a similar concept as dual carriageway in our legislation. (It is still being discussed what to do now, but just using lanes>=2 and oneway=yes seems to be slightly favoured).
So, anyway, to come to the point, I need the tag for articulated lorries to be able to describe in OSM tags the rules for GB:motorway.
I do NOT intend to tag every motorway there is in the UK with maxspeed:hgv_articulated=60 mph, that would be madness.
The OSM wiki is supposed to provide documentation on what’s in OSM for the benefit of the humans editing OSM; it has no purpose other than that. If you find that you’re copying piles of information in from elsewhere then quite frankly you are wasting your time - the information elsewhere will change, and your page will be out of date.
Your first three words at the top of this thread were “In Great Britain”. I had assumed that we were only referring to the “United Kingdom” row of the table at https://wiki.openstreetmap.org/wiki/Default_speed_limits. Incidentally there you have made a number of errors - you have documented both GB-SCO:nsl_single and GB-SCT:nsl_dual, neither of which are in use in OSM. Perhaps they ought to be, but you’d need to persuade the people on talk-scot and talk-gb of that rather than just writing a wiki page pretending that they already are.
The table is not final, its purpose is also to find out what tagging we need and you should consider it a courtesy I even put this in the wiki where any osm user can collaborate rather than just a JSON in some github repository.
Anyway, with such unfriendliness I am not going to waste my time to discuss this further with you. That reply was directed at hadw.