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#1
rudy

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Hello All -

Here's something to think about over the Christmas holidays. Has anyone come across a consistent and useful definition and classification of North American roads? Some are fairly easy and straigthforward (e.g. Free limited access multilane highways), others are a little more fuzzy (e.g. primary highway). Since, it seems, each province and state in Canada and the U. S. have a slightly different classification scheme, it would be nice to have a clear and consistent set of definitions that can be applied to all jurisdictions.

Rudy

#2
Hans van der Maarel

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Here's something to think about over the Christmas holidays. Has anyone come across a consistent and useful definition and classification of North American roads? Some are fairly easy and straigthforward (e.g. Free limited access multilane highways), others are a little more fuzzy (e.g. primary highway). Since, it seems, each province and state in Canada and the U. S. have a slightly different classification scheme, it would be nice to have a clear and consistent set of definitions that can be applied to all jurisdictions.


First of all, make up your mind whether you want a classification based on function or on appearance. This is my major pet peeve when working with data by the Dutch Topographic Service. A very extensive, ~100-class classification just for roads, based on appearance. Whereas I normally map them by function...
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#3
rudy

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First of all, make up your mind whether you want a classification based on function or on appearance.


How do you mean "by appearance?" By appearance on the map or by how they look in real life? I would tend to go for function - regardless of who operates or maintains the road (i.e. municipality, state, federal)

R

#4
Hans van der Maarel

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How do you mean "by appearance?" By appearance on the map or by how they look in real life? I would tend to go for function - regardless of who operates or maintains the road (i.e. municipality, state, federal)


By how it looks in real life. Which means there's different classifications for roads with and without a lane divider, to name just one example. The Topographic Service classification is very extensive and mainly based on real-world appearance (railroad with 1, 2, 3 or 4+ tracks, 4 different classes), although function does get taken into account at certain points.

What's really making it a very complex classification is the fact that there's only a single attribute (or, in the Microstation version, a unique combination of attributes) available for classification. So the entire roads classification is copied 3 times (to cater for "under construction", "in design" and "in tunnel".

So another recommendation is, if you want to store this, make sure you have an attribute especially for that... Right now, if I'd want to select all roads under construction, I'd basically have to get out the Excel table that holds the descriptions, looks for the ones I want, note down the numbers and then do a select on those in whatever GIS package I use.
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#5
natcase

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The National Highway Planning Network (NHPN) has metadata classifying Federal-aid highways as:
1: Rural Interstate
2: Rural Principal Arterial
6: Rural Minor Arterial
7: Rural Major Collector
8: Rural Minor Collector
9: Rural Local
11: Urban Interstate
12: Urban Freeway or Expressway
14: Urban Principal Arterial
16: Urban Minor Arterial
17: Urban Collector
19: Urban Local

Which works for a national map scale. It's the network in the National Transportation Atlas Database (NTAD)

The problem with sub-Federal aid highways is they actually are inconsistent in maintenance level from state to state. For example, Wiscsonsin "county roads" are all paved... some of them can only be considered in that you can detect bitumen among the gravel remnants, but... By contrast, there is at least one state highway in Minnesota that is still just gravel. So there's a lot more asphalt, although what there is may not be as well maintained, as soona s you cross the border. The Dakotas do not number county roads. Not at all. Which makes it look like we just for got to number west of the border on our state map. And so on.

The problem gets more extreme north of the border, where limited access were never the defulat mode for inter-province travel. Thus the clear national network of roads from the US to Canada seems to end suddenly at the border as liimited-access access highways become perfectly passable grade-access highways.

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#6
Mike H

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US State level data is more likely to classify roads by an economic factor, moreso than the descriptors mapmakers would prefer for visual classification. A Federal Highway, a State Highway, a county road, a township road, a private road - these are the categories that state planners rely on to allocate funding resources for maintenence. In a large, rural state like Maine I'm constantly trying to figure out if they are paved, gravel or dirt.
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#7
Charlie Frye

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I've found that there is no simple answer to this. At local scales there are many different schemes--Nat listed some commonly used "types". Texas also has ranch or farm to market, and there are others. The main issue to me, is that the road line should be symbolized according to capabilities or functional class, and labeled according to its adminstrative class. Thus, there are:

1. Restricted Access highways, which may be labeled as interstates, U.S. Routes, State Routes, or even county level routes.
2. Limited Access Highways, which may be U.S. Routes, State Routes, etc.
3. And so on

Whether you include a median, or additionally the type of median may be important. Whether the highway is a toll road or has a carpool lane, or an express (toll) lane also may be of importance.

Unfortunately, not all locales consistently use or define arterials, collectors, and local roads the same way. Major and Minor distinguishers are not always used. Highway ramps and frontage roads are not always considered consistently either. Private streets and trails also need to be accounted for. Then as Mike noted paved and unpaved is an issue.

Problems begin to arise for larger scale maps when you consider that main street in many a small town is a U.S. or State route. Thus, it should have both designations labeled on the map. Many highways routes also share pavement for a stretch, for example, locally, I have I-215 and CA-60 doing just that. A number of road GIS datasets have Alternate names included as attributes, but the functional class is not always correct, and the adminstrative class is only implied through the name.

So, my answer is once you get past the small scales, where using Interstates and Trans Canada, U.S. Routes, and then State or Provincial Routes, there's not much of a way to be consistent. Further, more than just taxonomic problems will arise; population density has a lot to do with what class of roads exist within a location. For instance, a 1:50K map in SW New Mexico will have different needs than a map of the same scale in NE New Jersey.

If you're compelled to show all roads, I would also say look at the USGS--they had to do this in making the 1:24K, 1:63K, 1:100K, 1:250K, and state map series--they punted. They made up their own much simpler classification system in order to gloss over all these details and problems.
Charlie Frye
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Software Products Department
ESRI, Redlands, California




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