[Tagging] maxwidth vs. maxwidth:physical vs. width

Kytömaa Lauri lauri.kytomaa at aalto.fi
Wed Feb 18 17:01:02 UTC 2015

Tobias Knerr wrote:
>The odd one out is clearly that introduction of the Key:maxheight page.
>And that also used to clearly state that the key refers to legal limits,
>until this edit:

The history of the descriptions is scattered among several pages, including at least:
Map Features

In 2006 (17 March), the original Map Features listed these tags as table rows:
Linear, Restrictions, maxheight, Num, height limit in metres
and so on, linking to the Key:access page.

Created on that same day in 2006, the original Key:access read just 

Section "General statutory restrictions" and later changed to "Size and statutory restrictions", included all max* and min* keys, i.e. also maxspeed and minspeed,
"The restricted width limit in metres, eg 2m" / "The restricted headroom limit in metres, eg 2.5m"

Even the page introduction didn't refer to "legal accessibility". Later the infobox one sentence description was written as "who may access an element", and this was changed on 10 July 2008 to "the legal accessibility of ...", here:

The examples of maxheight / maxwidth, a couple of lines above this, were changed only once, on 22 June 2011, link below, and are still ambiguous for the outcome of this discussion: "the maximum vehicle height is 2.5 meters" - this doesn't refer to physical nor legal. 

The page Key:maxheight at first (April 2008) just redirected to Key:access, and the "legal" bit was added on 31 July 2009:
This edit summary does refer to some "recent discussion in talk-mailinglist" for the change.

It IMO comes down to the different views of two starting points for the modelling:
1) are you legally allowed to crash a too tall vehicle to the bridge, if there's no height limit sign?
2) which is more important, the existence of traffic signs or whether a driver of a vehicle of height x can use that section of the road.

No matter what one answers to these, the keys *:legal= and *:physical= are explicit. And mappers can measure the clearance, e.g. with an ultrasound distance meter, even when it's not signposted.

If there's (I seem to have written these with maxheight, but the statements apply equally to width):

maxheight:legal=x, maxheight=x, one knows that x is a signposted limit.
maxheight:legal=x, maxheight=y (but y is smaller than x), then one knows there has to be something physical preventing taller vehicles passing
maxheight:legal=x, maxheight:physical=z (and z is larger than x), then one knows there's a sign, but even taller vehicles could get through if they have a permission, or other right to disobey the sign.
maxheight:physical=z, maxheight=y (where y is smaller than z), there's presumably a sign with the value "y".
maxheight:physical=z, maxheight=y (where y is larger than z), there's presumably a sign with the value "y", but it's wrong and a tall vehicle could hit the low hanging barrier.

On a related note, regarding the fact that when turning, the physical maximum width depends on the length of the vehicle: road planners have the concept of a "design vehicle" which roughly corresponds to the largest allowed vehicle in that vehicle category, and the turning radius such vehicles should be able to achieve. So a tag maxwidth:physical:hgv could describe how wide such a vehicle could be to be able to navigate that curve, supposing the other attributes of the vehicle would correspond to the design vehicle. That leaves a lot of cases undefined, but could be a start.


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