Yes, obviously. Taken from toad signs with numbers on them. Sometimes software can determine max speed based on whether a part of the road is inside place=* polygon, but it shouldn't be relied upon.
In an ideal world, every way would have a maxspeed value. We don't live in an ideal world, though. You can probably get away with omitting them on residential strets, but on the major streets and other roads they're more important for routers to be able to override their (often horribly optimistic) assumptions.
If they all had the same speed limit, barring some exceptions, you could tag the exceptions, and then use JOSM to find the remaining streets to tag in one go.
It's not going to happen. Too many roads drawn without limits. Too many variations on short stretches. It is part of my mapping routine now but life is too short to go through old data, except on an as and when basis.
This arose for me in a MapDust bug about route timing. Do I treat it as a throwaway remark from an annoyed motorist with too much spare time or a valid comment? Going with the second option I have to adjust to other people using this map differently. Speed limits and thus journey times, are an issue for some. Research in the Wiki shows it is a wide ranging issue. Having trawled through the Maps page (comment above) software writers might be working towards another solution.
And the speed limit doesn't really help with planning journey times - plenty of roads would be difficult to take at the limits (especially when stuck behind a micra doing 30mph on an NSL-60 road just outside an urban area)....
"So I typically add any exceptional speed limits that couldn't be implicitly derived." - although this obviously leaves the question in the mind of the next mapper - is this road NSL/standard for the limit, or is it unchecked?
Having all highways with a maxspeed tag set will happen before every house has a addr:housenumber - which is a goal that will take some years even in towns with active mappers. Just get on with it, you'll have your local area covered soon enough even if you collect just one speed limit every day. Make the most out of your mundane travels by introducing slight variations.
So it seems that speed limits are somewhat up in the air at the moment. Implicitness of tags on features has been a problem from the start of OSM. Whether highway=motorway means oneway=yes used to be a problem (maybe still is), and I suspect maxspeed=* is going to be the next issue.
I have been adding maxspeed=* tags to major roads (non residential) as I find out where their limits begin and end (or at least reasonably close). However, I don't bother adding any tags to ways where the road is the National speed limit. However, I notice the wiki mentioning source:maxspeed, so I may use that with explicit maxspeed on NSL ways.
I realise that most roads won't be passable at the speed the limit is, but I don't see how averagespeed=* could be used.
Personally, for NSL roads I tag the explicit number, if only because it's impossible to determine with any certainty what that would be from the data alone. A way tagged oneway=yes may be 30, 60 or 70mph, depending on stuff we can't reliably detect. A "restricted road" (30mph) is one where there is street lighting to a certain standard which lit=yes doesn't tell us (unless people are going to measure the spacing and tag them lit=45m or somesuch). A one-way road may be part of a dual carriageway, or it may not - consider the ring road in Stourbridge or the Redditch Ringway. IIRC, neither of these is actually NSL, so they should be tagged explicitly anyway, but it illustrates the difficulty of trying to detect which category a road should belong in. Then there are added complications involving motorways and the like - the A1 east of the Edinburgh Ring Road is explicitly signed as 70mph because it is not subject to the NSL (mostly an accident of history).
I don't buy the argument about the government changing the NSL, since local authorities can change speed limits in any case (my local authority in the last couple of years downgraded a lot of previously NSL roads to 40mph). source:maxspeed seems like a good idea, since this allows the combined cases of the government changing the NSL, and the fact that different vehicle types have different speed limits - e.g. HGVs limited to 40mph on single-carriageway roads.
In the city I live in, Seattle, WA, all streets have a speed limit of at least 25 mph. If this is true in your town, you could probably tag all residential streets with a certain speed. This is pretty tedious, though, and you can't count on every street having the same speed limit. The only good way to find out the speed limits is to drive around town making note of speed limits on certain roads.
OpenStreetMap
Discussion
Comment from Zverik on 27 February 2011 at 18:55
Yes, obviously. Taken from toad signs with numbers on them. Sometimes software can determine max speed based on whether a part of the road is inside place=* polygon, but it shouldn't be relied upon.
Comment from SuborbitalPigeon on 27 February 2011 at 19:55
Every single residental road? If so, that does make sense.
I also rather like the idea of toad signs (just kidding).
Comment from chriscf on 27 February 2011 at 22:46
In an ideal world, every way would have a maxspeed value. We don't live in an ideal world, though. You can probably get away with omitting them on residential strets, but on the major streets and other roads they're more important for routers to be able to override their (often horribly optimistic) assumptions.
Comment from SuborbitalPigeon on 28 February 2011 at 00:21
I see. It would be rather tedious to add maxspeed tags to the all the residential roads, it's tricky enough with the other roads.
Comment from chriscf on 28 February 2011 at 04:16
If they all had the same speed limit, barring some exceptions, you could tag the exceptions, and then use JOSM to find the remaining streets to tag in one go.
Comment from !i! on 28 February 2011 at 07:45
Right, personaly I map everything I see in Videomapping but normaly this is to much.
You might check out the maps presenting maxspeed colouring
http://wiki.openstreetmap.org/wiki/Maps
Comment from Saxton on 28 February 2011 at 10:02
It's not going to happen. Too many roads drawn without limits. Too many variations on short stretches. It is part of my mapping routine now but life is too short to go through old data, except on an as and when basis.
This arose for me in a MapDust bug about route timing. Do I treat it as a throwaway remark from an annoyed motorist with too much spare time or a valid comment? Going with the second option I have to adjust to other people using this map differently. Speed limits and thus journey times, are an issue for some. Research in the Wiki shows it is a wide ranging issue. Having trawled through the Maps page (comment above) software writers might be working towards another solution.
Comment from Jean-Marc Liotier on 28 February 2011 at 12:35
Type of road provides a reasonable default in most cases, so I guess that the focus of explicit speed limits should be where unusual ones apply.
Comment from Pink Duck on 28 February 2011 at 13:32
There are already default maximum speed limits on a per-country basis by highway type:
http://wiki.openstreetmap.org/wiki/OSM_tags_for_routing/Maxspeed
So I typically add any exceptional speed limits that couldn't be implicitly derived.
Though the last time I checked Skobbler didn't use any of the implicit defaults, hence a lot of missing speed limit reports on the MapDust site.
Comment from kevjs1982 on 28 February 2011 at 16:24
And the speed limit doesn't really help with planning journey times - plenty of roads would be difficult to take at the limits (especially when stuck behind a micra doing 30mph on an NSL-60 road just outside an urban area)....
"So I typically add any exceptional speed limits that couldn't be implicitly derived." - although this obviously leaves the question in the mind of the next mapper - is this road NSL/standard for the limit, or is it unchecked?
Comment from alv on 28 February 2011 at 16:48
Having all highways with a maxspeed tag set will happen before every house has a addr:housenumber - which is a goal that will take some years even in towns with active mappers. Just get on with it, you'll have your local area covered soon enough even if you collect just one speed limit every day. Make the most out of your mundane travels by introducing slight variations.
Comment from SuborbitalPigeon on 1 March 2011 at 01:25
Hello, and thank you for all your comments.
So it seems that speed limits are somewhat up in the air at the moment. Implicitness of tags on features has been a problem from the start of OSM. Whether highway=motorway means oneway=yes used to be a problem (maybe still is), and I suspect maxspeed=* is going to be the next issue.
I have been adding maxspeed=* tags to major roads (non residential) as I find out where their limits begin and end (or at least reasonably close). However, I don't bother adding any tags to ways where the road is the National speed limit. However, I notice the wiki mentioning source:maxspeed, so I may use that with explicit maxspeed on NSL ways.
I realise that most roads won't be passable at the speed the limit is, but I don't see how averagespeed=* could be used.
Comment from chriscf on 1 March 2011 at 16:27
Personally, for NSL roads I tag the explicit number, if only because it's impossible to determine with any certainty what that would be from the data alone. A way tagged oneway=yes may be 30, 60 or 70mph, depending on stuff we can't reliably detect. A "restricted road" (30mph) is one where there is street lighting to a certain standard which lit=yes doesn't tell us (unless people are going to measure the spacing and tag them lit=45m or somesuch). A one-way road may be part of a dual carriageway, or it may not - consider the ring road in Stourbridge or the Redditch Ringway. IIRC, neither of these is actually NSL, so they should be tagged explicitly anyway, but it illustrates the difficulty of trying to detect which category a road should belong in. Then there are added complications involving motorways and the like - the A1 east of the Edinburgh Ring Road is explicitly signed as 70mph because it is not subject to the NSL (mostly an accident of history).
I don't buy the argument about the government changing the NSL, since local authorities can change speed limits in any case (my local authority in the last couple of years downgraded a lot of previously NSL roads to 40mph). source:maxspeed seems like a good idea, since this allows the combined cases of the government changing the NSL, and the fact that different vehicle types have different speed limits - e.g. HGVs limited to 40mph on single-carriageway roads.
Comment from compdude on 1 March 2011 at 16:39
In the city I live in, Seattle, WA, all streets have a speed limit of at least 25 mph. If this is true in your town, you could probably tag all residential streets with a certain speed. This is pretty tedious, though, and you can't count on every street having the same speed limit. The only good way to find out the speed limits is to drive around town making note of speed limits on certain roads.