Road Speed Limits

[Funkytoad]

Please forgive me if the answer to this is clearly posted somewhere. I was unable to locate it.
I am curious what the policy is regarding speed limits. I would assume that they should be the posted speed limit that one might find on a sign on that roadway. Is that correct?
I ask because I have been working in some areas where nearly every road (mostly minor arteries and freeways) are listed as five miles per hour over or under the posted speed limit. I wasn't sure if there was a reason for this. I can see where some roads have been reverted to the default speed for their priority, which explains it to some degree. Should I be changing these speed limits to reflect the posted limits?

[Wthrwyz]

Yes, the speed listed in Map Maker should match the posted legal limit.

That said, the system has both a default speed and an acceptable range for each priority level.  If someone (or some automated refresh/cleanup process) changes a road's priority or deletes a road and redraws it, it may end up with whatever the system's default speed is unless the editor was paying attention.  As for acceptable values...try setting a terminal road to a 60 MPH speed limit and the system will tell you off pretty quick.

At any rate, if something is reverting proper speed limits to standard values, then it's likely an automated system going haywire because the speed limits are supposed to match reality.

[biitrix]

and Yes, the priority names and default speeds make very little sense in rural Canadian and US areas. Across Alberta and Saskatchewan the speed limit on most gravel roads is 80 km/h - They're all "local roads". Paved roads outside of built up areas are usually 100 km/h. Divided highways are either 100 or 110km/h - and any of the aforementioned paved roads could be anything from a minor artery to a freeway. Almost all non-artery in-town roads are 50 or 60 km/h (except alleys) 

In Montana if a road has asphalt the speed limit is usually 70 mph once you're out of a built-up area. The Interstate highways are 75 mph

What does this mean to us? It means that nearly all of the speeds attached to the zillions of road segments covering most of North America - are wrong.

How do you fix them?  One. at. a. time. and. you. will. wait. for. moderation. with. each. one. so. why. bother.

It would be truly glorious to have an interactive color-coded speed-limit map (the term in graphics parlance is "heat map") that could be used to do batch-fixes of stuff like this. 

[LVI56]

I spent about two days changing speed limits on just the minor arteries of a city in my area. In some cases they were 20mph slower than what was posted. That makes a huge difference in calculating travel time for directions.

[- deltafox -]

Le dimanche 8 janvier 2012 04:14:41 UTC+1, Wthrwyz a écrit :

Yes, the speed listed in Map Maker should match the posted legal limit.

Yes... and no ! Google contradicts itself on that:

Here, it says that speed attribute should correspond to average speed, so that times of travel calculations be accurate :

"Avg speed

Specify the average speed of the road here in mph (miles per hour) or km/h (kilometers per hour) based on the default value of the country. Speed is used to generate appropriate routes and travel times for directions on maps"

If you click on "Learn more", it says, at the contrary:

"The Speed attribute should represent the legal speed limit for an entire stretch of road. Advisory speed limit signs (frequently identifiable by a yellow or orange sign color) are usually used to indicate a recommended speed for a ramp, sharp turn, or other part of a road that might be best driven at slower speeds; since these are not legal speed limits, they should not be used to set the Speed attribute"

This is a non-sense ! Average speed cannot be equal to legal speed limit ! Travel times have to take account of advisory speed limits when present, and be at least 5 to 10% below legal/advisory limits to be on the safe side. Furthermore, there are many small roads in mountains or difficult terrain with sharp turns and no specific legal or advisory speed signs, maybe just a Danger Sign, or nothing on smaller roads ! In this case, average speed may be only 40 or 50 km/h with a legal speed of 90 or 100 km/h, this makes a lot of difference ! As a result, Directions ARE wrong. And this not only theoretical: I remember once having followed Google Maps directions on a small mountain road such as this, when directing through a better road slightly longer would have saved me at least a considerable time.

I understand that "Legal Speed" are also important (for speed control systems), but there should be 2 separate attributes, "Legal Speed" and "Average Speed". 

[biitrix]

Good point deltafox!!  I suppose this is where the Regional Experts would be most useful. What we're building here is a virtual model of the real-world road network. It's amazingly detailed, and has the potential to be amazingly accurate. When road priorities are set correctly GM can get me from A to B even faster than local drivers, but I have also seen where it would have picked a much inferior route based on driving time because a 70 mph road was saved with a 50 mph attribute.

In rural western Canada (I don't know much about the east), and the rural parts of the US states I'm intimately familiar with like Montana, Idaho, Utah, Nevada, Arizona, and northern California we measure time between places in hours (Q: Where do you live? A: About an hour south of {city}) and the real-world defacto speed is 10% above the posted limit. This assumes daytime dry-road conditions. Allowing for quick bathroom breaks, the (distance/speed limit) = time formula works with surprising accuracy.

In urban areas, it would be more useful to know the *real* average speed, per segment, per hour of day, per day of week - or define the hours of morning and evening traffic congestion, and what's the real speed then... I bet routing would change if the 100 km/h road with high priority but a 20 km/h rush hour speed was compared with the 60 km/h minor artery that flowed along nicely at 50 km/h during the same time. The beauty of this would be that you'd add more intelligence to the routing algorithm (by an order of magnitude) *and* you wouldn't need to fuss with the real-time traffic flow stuff for trip planning. It would work well nearly all the time! 

With the number of Android phones out there, I don't know why Google hasn't included a voluntary app to collect anonymous road segment / day / hour / speed data. For holidays use the default speeds, or use the weekend flow patterns. Include the planned road closure info from the cities and the highway construction dates/times/ special speed limits from the various DOT's and you have some freaky good info to do trip modelling with.

--- Hey Google - here's your next software patent!  Don't forget who your friends are :)

[Борис]

So? Average or legal? I mean sometimes in the city although the speed limit is 60 km/h you normally barely make 30 (unless near midnight). I'd be happier if google would tell me i need 30 minutes from point A to B and it would turn out to be 15 that it telling me 15 minutes when the trip takes half an hour. In Peru the case is, for example if you want to drive from Lima to Cuzco City Google tells you you need 13 hours when you actually can't make it in less than 20, so it's a big difference.

[DdDave]

Use legal.

All the responses I've seen from Google employees agree that it should be the legally posted limit.  The problem with trying to determine a true "average" is that it's going to be time dependant (slower in rush hour, faster at 3am).  They have to draw the line somewhere and can't start having all of the trip calculations to be a function of the departure time and how many pee breaks you take, you just need to know to leave yourself more time in rush hour.

[Boris Villagarcía]

Then they should really change the field name to "Speed limit" or "Avg speed limit". Because the actual name is kinda misleading.

On Thu, Jan 19, 2012 at 3:12 AM, General Map Maker on behalf of DdDave <google-...@googlegroups.com> wrote:

Use legal.

All the responses I've seen from Google employees agree that it should be the legally posted limit.  The problem with trying to determine a true "average" is that it's going to be time dependant (slower in rush hour, faster at 3am).  They have to draw the line somewhere and can't start having all of the trip calculations to be a function of the departure time and how many pee breaks you take, you just need to know to leave yourself more time in rush hour.

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[delta fox]

Did you see any response from Google employees ? they just ignore our concern :-(

And, it's not advisable to use 'legal speed' when the label for the field is 'average speed' !

But I agree with you that it has to be independent of traffic (computed time is supposed to be correct when there are no traffic jam, the user can add extra duration at rush hours)

[Moid]

Hi Everyone,

Sorry it took us a while to post back. 

As you have correctly pointed out, a road segment gets assigned a default speed, depending upon its priority. However, if you're certain that a certain segment has a particular ‘speed limit’, you can assign the specified speed as the average speed. 

As for the discussion pertaining to whether ‘Advisory speed limit’ or ‘Legal speed limit’ should be used, the answer is the legal speed limit. 

Also, as much as we'd like to provide that functionality to our users, the current computed time is independent of traffic and duration of the day. 

Regards,

Moid. 

[Andrew Sawyer]

Moid, thanks for your clarification. I have a question about freeway ramps and their speed limits. In NH, USA the legal speed limit for ramps is the posted speed limit for the freeway. I have in the past posted ramps with a 55mph or 65mph but these have been commented on by GRs that the speed is not appropriate. is it permissible to post the legal speed limit or should we use the suggested posted speed limit (yellow sign) on said ramps?

Sent via BlackBerry from T-Mobile

---

From: General Map Maker on behalf of Moid <google-...@googlegroups.com>

Sender: General Map Maker on behalf of Moid <google-...@googlegroups.com>

Date: Sun, 19 Feb 2012 22:38:43 -0800 (PST)

To: <google-...@googlegroups.com>

ReplyTo: General Map Maker on behalf of Moid <google-...@googlegroups.com>

Subject: Re: Road Speed Limits

--

[Moid]

Thanks for replying back Andrew. To answer your question, the permissible legal limit should be used. We have communicated with our reviewers about the same.

Moving forward, if you come across any comment which says otherwise, please post back with the link.

Thanks,

Moid

[delta fox]

Moid:

You reply is appreciated. I notice also that the help balloon has been changed accordingly (from 'average speed' to 'max speed') very recently. But there are still a few questions :

- the ballon still says that the purpose of this field (Max Speed) is "to generate appropriate routes and travel times for directions on maps" -  if the max speed attainable due to the route condition or geometry is much lower than legal limits, and the 'legal speed' is entered, both travel times and routes will be inappropriate ! Why is the legal limit so important for you, if this limit may not reasonably be achieved ??? For instance, a small unpaved road in mountaineous terrain will likely have no specific legal limit, so that the general limit outside towns will apply (100 km/h), whereas the maximum achievable speed may be 30 km/h at most !!!

- when default speed, depending upon priority, are not equal to the legal speed limits in a particular country, could the default values be corrected in the system ??? 

- in addition to Andrew's concern above, not only the Reviewers but the system itself may make impossible to set the legal limits to a particular segment: for instance, the system does not let a Freeway or Expressway have any speed under 60 km/h - but some freeway exchange roads, in sharp turn, or roundabouts connecting two expressways, do have a lower legal limit (30 km/h for instance). We can communicate with Reviewers, but the System does not allow us to validate the correct speed ! Shouldn't be possible to override this limitation (eventually with a warning and moderation, like in other cases when a parameter look strange to the system) ???

[delta fox]

Erratum:

The name of the field is different from one country to another (!). in the US, as stated above, it says 'Max. Speed' - in other countries, as in Morocco, it still says 'Avg. Speed', with help ballon 'Specify the average speed of the road here in mph (miles per hour) or km/h (kilometers per hour) based on the default value of the country...'

This may be the Mountain View modern variant of old saying "Vérité en-deçà des Pyrénées, erreur au-delà" ;-)