On 24/05/18 13:47, Tod Fitch wrote:
On May 23, 2018, at 7:57 PM, Paul Johnson <[email protected]
<mailto:[email protected]>> wrote:
On Wed, May 23, 2018 at 10:34 AM, Tod Fitch <[email protected]
<mailto:[email protected]>> wrote:
On May 22, 2018, at 12:48 PM, Paul Johnson <[email protected]
<mailto:[email protected]>> wrote:
In the case of your typical bog standard American residential
street, I'm strongly disinclined to agree that this is a two
lane situation. I'd be inclined to mark unpainted lanes in the
cases where channelization regularly occurs without the pavement
markings anyway. This isn't the case on residential streets, as
people will tend to drive right up the middle of such streets,
only movingly right to meet oncoming traffic and maybe when
approaching a stop sign.
Hmmm. I guess driving culture may vary from place to place in the
US. I always keep to the right regardless of the existence of a
lane markings. I will admit, however, that traffic studies
indicate that the average driver will be a bit more to the center
of the pavement if there are no lane markings. Similarly, at
least in residential areas, it has been found that drivers will
generally go slower if there is no center marking. At least that
is the rational my local government is using to remove the center
divider marking for traffic calming purposes.
While this may be true, most people will shy towards center (and
perhaps even stay in center) for most of their trip down a standard
width street (which, while typically 40 feet, this is /inclusive/ of
all features including sidewalks, making the effective width of the
roadway closer to 25 feet, a random pull from Mesa, Arizona's design
guide <http://www.mesaaz.gov/home/showdocument?id=1044> blindly from
Google confirms this, with their design guide being 27 feet across
between curbs), means that two full size pickups can (barely) pass
two cars parked on opposite sides of the street at once. That's also
generously wide compared to a lot of places, many suburban and small
town residential streets I've encountered are open-edged with parking
off the paved area, and the paved area being maybe 20 feet on a
particularly wide street. New urbanist street designs are similarly,
deliberately, narrow as a traffic calming measure, as parked vehicles
will tend to provide de facto ad hoc chicanes. As such, if lanes are
marked at all, it's usually at the very ends of blocks only, where
parking is prohibited, as a confirmation that the street is indeed
two-way and provide a hint as to the default passing rule.
I have noticed that newer developments, especially infill development,
have narrower residential roads than where I live. And I admit I did
not look up current design standards. I simply took a tape measure to
a number of residential streets in my neighborhood. The one in front
of my house is 40’0" +/- 1" between the curbs. There are sidewalks but
I excluded them from my 40’ number. Subjectively my current street
seems about the same as others in the area and the same as my in
previous neighborhood in a different city. Both neighborhoods are
older, laid out when accommodating the automobile was high on the list
of design criteria. It would be interesting to pull out the design
standards that were in effect in the 1950s, 60s and 70s when much of
our current suburbia was created. I would not be surprised if a lot of
our current stock of residential roads are wider than the current
standards specify.
By the way, I don’t see a way to tag the accuracy or confidence level
for a measurement. Seems like we ought to have something like
*:confidence=*, similar to the *:lanes tagging so we could, for
example tag the width of a road as:
width=18’0"
width:confidence=2’0"
The metrology term is 'uncertainty' .. so
width:uncertainty=2'0"
To be complete there would need to be a statement of level of confidence
and coverage factor.
However, for OSM simplicity, it could be assumed to have a normal
distribution covering one standard deviation .. making the confidence
level ~68% and the coverage factor ~1.
Of course the stated confidence level and coverage factor would be
assessed by the next metrologist.
There is a rough wikipedea thing on it .. it is rough.
https://en.wikipedia.org/wiki/Measurement_uncertainty ...
Best to look at the second reference in that wikipedia page ... NPL do
good articles.
If you are only estimating from the most likely source (allowable
imagery) then you probably are not going to be much closer than 0.5
meters or a couple of feet.
A confidence/accuracy tag would probably be another can of worms. How
are you determining it? Statistically? One sigma? Two sigma? Or assume
a single measurement but with a technique known to some typical error
pattern?
But I digress.
I know that road design varies over the world and even, to a
certain extent, within different states in the United States. So
this discussion is showing different regional points of view. A
typical, or to borrow the UK slang “bog standard”, American
suburban residential street is wide enough for parallel parking
on each side and space for trucks/lorries to get past one another
[1]. Typical parking lanes are about 8 feet (2.4 meters) and a
typical traffic lane is 12 feet (3.7 meters). So a total pavement
width is typically around 40 feet (12.2 meters). In some parts of
the world, even in older crowded US cities, a road of that width
might be striped for four lanes of traffic. But a typical US
residential street has no lane markings.
US tends to favor 9 feet per lane and 6 or 7 foot parking strips for
a full size residential street (and combine with 6 feet being the
minimum, 7 becoming common, and even wider in some places for the
bike lane, this will feel quite clausterphobic and many, if not most,
drivers who will yield the entire space to a vehicle passing a parked
vehicle first to stay out of the door zones). Per federal
guidelines, a boulevard would be at least 10, preferably 11 foot
lanes (and this will still feel quite narrow to most American drivers).
I can see the logic of only using the lanes tag if there is paint
on the pavement. But that leads to another issue: It is pretty
easy from experience to glance at a photo of a road and say it is
wide enough for two lanes of traffic. But it is much harder for
me to determine a width accurate to a couple of feet. I don’t see
a way to show a measurement error estimate [2] and listing
something as width=40'0" implies much more accuracy than a guess
based on a quick visual survey or imagery actually provides.
Look for the wear marks, these will be quite prominent in sun-prone
areas and where concrete is used. Generally speaking if there's
defined lanes that are just worn off, there will be wear marks where
passing motorists have rolled the same spot repeatedly. This can
often be confirmed with your favorite license-compatible street-level
imagery or a survey. Though if you're using JOSM and have suitably
high resolution aerials available, you can use JOSM to draw a line
perpendicular to the way from curbface to curbface to find the width.
My current favorite license compatible street level imagery is from my
dash cam. :)
I am considering getting another dash cam and rigging up something so
that it faces out a passenger side window. I figure that would be a
reasonable way to capture a bunch of shop details that I can’t get
with a forward facing camera.
Fortunately, or unfortunately depending on how you look at it, the
lane markings in my area are kept in fairly good repair so seeing
where they are worn off is often not possible.
I am rambling. To the point, if I were to add my photo [1] to the
urban highway tagging examples page of the wiki [3] what tags
should it have. My current guess is:
highway=residential
parking:lane:both=parallel
sidewalk=right
surface=asphalt
width=40'
For the specific example given by the photo, what tags would you
suggest.
Probably closer to 34'0" wide (we're still in agreement on customary
units that the inches should be included even when not necessary when
tagging?), since those vehicles are narrower than a full size pickup
(typ. 7 feet) and up against the curb, and so I'm reasonably sure
there's not more than 22 feet between them, but more than 18 feet.
I'd still leave off the lanes.
Only issue with fully specifying feet and inches is that it implies
inch level accuracy with I doubt any of our road mapping achieves. See
above for a digression on tagging accuracy/confidence levels.
I guess the question is: Would you leave off the lanes=* regardless of
the width as long as there is no painted center line? If it is width
dependent, at what width would you add a lanes=* tag even if there was
no center line painted.
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