Re: [Talk-us] Speed limit editing in Detroit

[Tod Fitch]

> On May 6, 2017, at 1:11 AM, Paul Johnson  wrote:
> 
> 
> 
> On Sat, May 6, 2017 at 3:07 AM, Paul Johnson  > wrote:
> 
> 
> On Fri, May 5, 2017 at 7:55 AM, Horea Meleg  > wrote:
> 
> A lot of motorway_links don’t have a speed limit sign. Do you have any idea 
> where could we get the speed limit values from?
> In North America, ramps with speed limits are relatively rare, but following 
> the usual rule that the previous speed limit applies, the speed limit of the 
> off-ramp would be the same as the freeway itself unless otherwise posted, and 
> if the same ramp returns to the freeway contiguously, that speed limit would 
> continue to carry over to the on-ramp.  It's not very much more complicated 
> than that, but in practice, just leave off maxspeed on the ramps entirely 
> unless it's actually posted with a regulatory (white sign) speed limit or a 
> general speed limit is known (both relatively uncommon). maxspeed:advisory 
> would be far more common, as exit ramps are nearly universally posted with an 
> advised (yellow sign) speed.
> 
> Adding to my own answer again, I should say rather than "in practice, just 
> leave off maxspeed" but rather, "in practice, it never comes up so people 
> rarely tag it."  I don't mind adding these if folks consider that favorable 
> (I do see the value).
> 

From a end user of a routing app on my phone that uses OSM data, I’d rather 
have the maxspeed omitted from *_link ways if it is not signed. The reason is 
that there are some freeway/freeway ramp geometries where traveling by the ramp 
is slightly shorter than keeping on the freeway. I’ve seen cases where that 
caused the app I use to route me off the freeway and then immediately back on. 
If there is no maxspeed tag, I can set the default for the *_link such that I 
am not needlessly routed off and then back on a freeway.

I guess that is “omitting tags for the data consumer”, but since we are 
discussion situations where there is no sign and, in general, we tag what we 
see I don’t see that as being too far from the normal tagging philosophy.

Cheers,
Tod


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Re: [Talk-us] Speed limit editing in Detroit

[Paul Johnson]

On Sat, May 6, 2017 at 3:07 AM, Paul Johnson  wrote:

>
>
> On Fri, May 5, 2017 at 7:55 AM, Horea Meleg 
> wrote:
>>
>>
>>1. A lot of motorway_links don’t have a speed limit sign. Do you have
>>any idea where could we get the speed limit values from?
>>
>> In North America, ramps with speed limits are relatively rare, but
> following the usual rule that the previous speed limit applies, the speed
> limit of the off-ramp would be the same as the freeway itself unless
> otherwise posted, and if the same ramp returns to the freeway contiguously,
> that speed limit would continue to carry over to the on-ramp.  It's not
> very much more complicated than that, but in practice, just leave off
> maxspeed on the ramps entirely unless it's actually posted with a
> regulatory (white sign) speed limit or a general speed limit is known (both
> relatively uncommon). maxspeed:advisory would be far more common, as exit
> ramps are nearly universally posted with an advised (yellow sign) speed.
>

Adding to my own answer again, I should say rather than "in practice, just
leave off maxspeed" but rather, "in practice, it never comes up so people
rarely tag it."  I don't mind adding these if folks consider that favorable
(I do see the value).
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Re: [Talk-us] Speed limit editing in Detroit

[Mark Wagner]

On Fri, 5 May 2017 12:55:55 +
Horea Meleg  wrote:

> Hello all,,
> Me and my Telenav colleagues are planning to start editing speed
> limit in Detroit area and we found the following situation:
> 
>   1.  There's a trunk road which continues with a motorway but we
> don't have a speed limit sign at the beginning of the motorway. Do
> you think we should add the speed limit value from position 1 or 2 on
> the highlighted segment? 42.4985931, -83.3042949 --> Position 1 (50
> mph) 42.4941433, -83.2950564 --> Position 2 (70 mph)

The speed limit from (1) should be used.  A change of road
classification doesn't automatically imply a change in speed limit.
 
>   1.  A lot of motorway_links don't have a speed limit sign. Do you
> have any idea where could we get the speed limit values from? Thank
> you, Horea Meleg

In general, motorway_links to a motorway are treated by everyone
(drivers, police, courts) as having speed limits equal to the speed
limit of the motorway they provide access to.  Links from a motorway
are treated as a "transition zone" where you are expected to be going
the motorway's speed limit at the start of the link, and the
destination road's speed limit at the end.  Advisory speed limit signs
are common, while signed mandatory limits are extremely rare.

-- 
Mark

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