Talk:Highway tag usage
Interstate highways should always be tagged with highway=motorway.
US Highways should be tagged with highway=primary. State Highways and County Highways should be tagged with highway=secondary. Any of these which is a divided highway with high speeds (65mph+), non-limited access (i.e. at-grade intersections) should be tagged with highway=trunk.
- In Maryland, I know, and most other states, I believe, there are no roads other than motorways with speed limits of 65 mph, and none at all higher. This then suggests that "trunk," an unusual word in the US, should represent an unusual class of road. I take the view instead that "trunk" is simply the highest class of nonmotorway.
- But then what do you consider a "nonmotorway"? Just because "trunk" is not in common usage here doesn't mean it shouldn't be used. If the tagging guidelines are clear, it will be used. See my longer discussion below. --SiliconFiend 00:43, 14 November 2007 (UTC)
- Being a "US Highway" does not correlate well with anything worth indicating on a map: physical attributes, use, even legal status. Also, if everything short of a US Highway is no better than secondary, we'll have a boring lot of secondary roads.
- True; I'm in favor of fine-grained classification as best as we can make it. --SiliconFiend 00:43, 14 November 2007 (UTC)
- There are also no numbered "county highways" in Maryland.
- There are in California and many other states. They seem to be more common in rural areas, particularly where the roads are laid out in a grid. If you don't have county highways, consider using my guidelines below to pick a classification. --SiliconFiend 00:43, 14 November 2007 (UTC)
Sometimes a tertiary road will be physically larger than a primary or secondary road. This is acceptable.
Alleys should be tagged as highway=service.
- I believe the following is a better clarification for our use in the US:
In OSM language the Highway feature is used to designate what we call roads.
A motorway is a four+ lane, limited access, grade separated freeway. These can include Interstates, US Highways, State Highways, County Highways or even Farm to Market Roads if they meet certain criteria. These criteria are limited access,the use entrance/exit ramps to access the freeway. Intersections with other roads are at grade separated crossings or ramps. A grade separated crossing means one road goes over or under the other. (ie. over/underpass) When Motorways meet other motorways they generally use ramps that are classified as Motorway Link. These motorways usually connect to other cities or move the traffic around and through a city. Limited access ring roads usually fall in this feature class also.
A trunk is what a motorway becomes when it loses one of it's criteria. This usually occurs to US, State, County highways as they move outside the urban areas. Intersections with other roads can occur at grade and/or when ramps are no longer needed to access the road. Usually they remain 4+ lanes and may or may not be divided by a physical median.
A primary road can be a US, State, County Highway or other road that connects two cities or moves traffic from one part of the city to the other. These are the highways that become Main St when they go through a small rural town. They will have traffic signals when they reach more densely populated areas. These are the roads you jump on when the freeway has an accident and you don't want to sit and wait it out.
A secondary road moves traffic within a city. It would service only a certain area within a city.
A tertiary road connects the residential roads to the higher classes: motorway, trunk, primary or secondary.
- That sounds (mostly) good to me. I'd like to clarify something about "limited access" as not everybody knows what that means. If properties along a road have direct access to that road (such as a road dotted with houses or businesses along it) then it's not "limited access" as I understand the term. Also, I'm really not sure about such a broad use of "highway=primary". These show up at a significantly low zoom level, and I think they should be reserved for significant regional routes (which aren't motorway or trunk). US routes just about automatically qualify. Beyond that, I'd only want to include state highways which are important connectors in the context of the US and Interstate highway systems. To include every road that "becomes Main St when it goes through a small rural town" would clutter up the map with a zillion red lines. (There are a LOT of small towns which aren't located on significant highways. Some of them are located on railroad lines, and their Main St become ordinary farm roads outside of town that don't really go anywhere important.) Since Secondary also shows up at a fairly low zoom level, I'd suggest that it be used for State routes and significant local routes. If a major urban street has a lot of lanes and a high traffic, I don't think that alone should qualify it for primary or secondary. Most of that traffic is probably local; there's just a lot of it because it's in a big city. On the other hand, if the road also makes sense as a city-to-city route, then a higher designation makes sense. Vid the Kid 02:03, 13 July 2009 (UTC)
On another note, I'd like to point out another reason to keep the Primary and Secondary designations mostly to US and State highways: so the routes can easily be traced on a map. Take a look at a street map of a decent-sized city. You'll notice that the US and State routes are colored differently, whereas other major roads in the city aren't drawn much differently from the minor streets. The practical reason for this is to allow the reader to quickly see what streets carry the designated routes. If line styles were determined primarily from physical characteristics of the roads, this would be more difficult. In cities where the numbered routes make several turns, the only way to indicate the course these routes take would be to put route markers on almost every block. If we reject the idea that a road's route designation is a significant factor in determining its importance (I don't reject that idea, but I also recognize it's not the only factor) then we will have that problem. Maybe the solution here is to have the renderers identify the numbered routes continuously, like with highlights "behind" the roads. The US routes would be one color, state routes another... then again, maybe that's better left to a new renderer specialized in automobile travel, similar to CycleMap. (Since OSM is sort of turning into a map of everything, the usefulness of the main slippy map for road navigation is diminishing slightly.) Vid the Kid 02:03, 13 July 2009 (UTC)
These guidelines may not be ideal for the US. The vast majority of public roads there meet the physical standards for primary highways. Thus a map focusing on physical attributes may be monochromatic. Possibly the most useful attribute to represent is neither physical nor legal, but some (admittedly subjective) judgment about the use. Given two routes of approximately equal length connecting the same places, which is the main road, to be preferred for quick motor travel, and which the proverbial Blue Highway, better perhaps for cyclists or leisure drivers?
--Tompermutt 16:33, 1 October 2007 (BST)
Agreed. The criteria listed on the Wiki page promote too many highways to "motorways". It's too hard to distinguish between them; in dense urban areas you could end up with a lot of "motorways". It seems to me the "motorway" tag should be reserved for interstates, with some exceptions for major US highways. You left out "tertiary" from your descriptions. I would see "tertiary" as an important thoroughfare road through a town--higher speeds and less traffic controls than "unclassified". How about these guidelines, based on speed limits and lanes:
- motorway: Interstate, 2+ travel lanes, ramp access only, speed limit 65 MPH+
- trunk: US highway, 2+ travel lanes, ramp access only, speed limit 60-70 MPH
- primary: US highway, 1-2 travel lanes, or State highway, 2 travel lanes, speed limit 55-65 MPH, can have occasional stoplights/traffic controls
- secondary: State highway, 1-2 travel lanes, or larger county highway, speed limit 45-55 MPH
- tertiary: County highway, other unnumbered thoroughfare, speed limit 40-50 MPH
- unclassified: urban commercial district or rural low-density housing, normally no direct driveway access to housing in urban or suburban areas, speed limit 30-40 MPH
- missing_tag: It seems like there needs to be another classification for residential branch roads which are main roads through subdivisions but still have direct driveway access to housing.
- residential: urban or suburban roads primarily for providing access to housing, speed limit 15-25 MPH
--SiliconFiend 19:13, 8 October 2007 (BST)
- Further notes: In California, a "divided" road is always at least 2 lanes in each direction of travel. I know that's not the case in all states, though. I changed the criteria to clarify this.
- I think the classifications have a lot to do with expectations, too. To my knowledge, an interstate will always be at least 2 lanes, ramp access only, 65 MPH+. The same cannot be said of US highways which, in more rural areas, frequently pass through towns with grade crossings and are subject to stoplights and other traffic controls. This is another argument to restrict "motorway" to interstates only. State and county highways are generally slower than US highways (corners aren't straightened out as much) and are more likely to encounter traffic controls. Also, the road surface is generally better maintained for interstates than US highways, and US highways than state highways. I know that's not universally true, but you're more likely to encounter large potholes on state and county roads. --SiliconFiend 00:44, 14 November 2007 (UTC)
- I think the primary/secondary classification should take account of the shoulder, just to differentiate the two. Primary roads have 2 lanes with wide, paved shoulders which make the road safer to travel at 60-65 mph. This covers most 2-lane US highways and a few state highways. Secondary roads typically have 2 lanes with narrow to nonexistent shoulders; speed is limited to 55 mph or less for safety. This covers most state and county highways as well as some sections of US highways.--Elyk 04:20, 26 August 2008 (UTC)
"Motorway" I understand to be British for what is called a freeway in California, an expressway in some eastern US cities, and an "interstate" in many places in between where there are no examples besides official Interstate highways: a road with bridges and ramps instead of intersections. I don't remember ever seeing a map that didn't either render these all alike, or distinguish only free from toll. I suppose there will eventually be greater and lesser freeways, but I'm still happy with a single class for these.
I did leave out tertiary and unclassified. We'll see what others say, but for me four classes besides motorway (trunk, primary, secondary, residential) may be plenty. Indeed, it looks to me like most contributors so far use even fewer, perhaps because they are reluctant to use "trunk" which has no meaning to most Americans.
- I've been using "trunk" as an upgrade for roads that are primary/secondary by designation (US and State highways) which are divided and high speed (65+) but are not grade-separated. --Hawke 00:02, 29 January 2008 (UTC)
Note also that divided highways are supposed to be mapped with double traces, so that even if we think dividedness is important (which I'm not sure of), it is redundant to fold it into the classification as well. --Tompermutt 23:59, 14 October 2007 (BST)
Some attention also should be paid, I think, to roads as a network rather than in isolation. It looks silly for a primary highway to peter out in the countryside: it should usually connect to another primary highway unless it ends at a town or other significant destination. After all, it's a primary highway because it's the road to somewhere.--Tompermutt 14:04, 19 October 2007 (BST)
There is conflicting information about this, especially in the US, at several places. I suggest the subject be discussed on this page with a view toward unification. I've tried to collect here what I could find elsewhere, and to link here from other entry points:
I think it's important to have some guidelines, and I think the international ones (to the extent they are even consistent themselves) need some adaptation to the US. At the same time, I think classification of roads and networks of roads is a creative part of mapping, and I wouldn't like it reduced to a mechanical checking of legal status or width.--Tompermutt 16:31, 12 November 2007 (UTC)
- I think it's entirely appropriate to change the classification of a road at the point where the physical characteristics change, even if it seems to "peter out". It's common for a road to scale up from 1 travel lane in each direction to 2 or more as it approaches a city. That change doesn't happen at the city itself, but somewhat farther out at the point where traffic starts to increase. --SiliconFiend 00:43, 14 November 2007 (UTC)
- I've been using "secondary" for county highways, and "tertiary" for that missing_tag you suggest. My logic is that many county roads are equivalent (physically) to the state roads. Also, "trunk" does not need to be limited access (ramps etc.) --Hawke 16:27, 29 February 2008 (UTC)
I have tweeked the wording of various road classes in the associated article and would appreciate people seeing if they agree with me. I suspect that some of what I have done will have been helpful, but some may not have been, so feel free to keep tweeking.
I have added a section clarifying the importance of the road hierarchy, such that a motorway is for more important (bigger) roads than trunk and trunk is more important roads that primary etc.
I have clarified that link roads (ie motorway_link and trunk_link etc) should be classed according to the more major road involved (for example that the link between trunk and motorway should be motorway_link not trunk_link etc). PeterIto 16:32, 20 April 2008 (UTC)
- I notice that highway=service is not listed on this page. Is there a reason it's not? --Hawke 17:15, 21 April 2008 (UTC)
- When I originally wrote this I was concentrating on what I had used so far in Korea. --Korea 10:10, 22 April 2008 (UTC)
Usage guide vs. Key:highway
I thought that highway:tag was just supposed to be a description of common values. In a job I had once the standards manuals just had a description of the fields and told you nothing about how to use them. I saw some logic in this. I think most of the how to use information should be moved here from Key:highway. --Korea 10:14, 22 April 2008 (UTC)
Agreement not reached yet?
This discussion seems stale, so I'd like to jump start it again with my thoughts.
In the US, Interstates clearly qualify for highway=motorway status. The US Highways are a little unclear. When they pass through cities, they often become major traffic-carrying roads with lights and low speed limits. When they are in the expanse between cities, they often are long uninterrupted stretches of road with few intersections and fewer lights. Thus it sounds like highway=trunk is too high a classification for them inside a city, while highway=primary might be too low outside of the cities.
Furthermore, there are sometimes roads which meet the criteria for highway=motorway (divided way, no at-grade intersections, high (55+) speed limit) but aren't really "on par" with the rest of the motorways. New Circle Rd encircling Lexington KY is a good example; it's a state highway (KY 4), but not US Highway or Interstate.
Lastly, the important information about "is this road a US Highway or Interstate" can be obtained through the route relations, so the tagging of a road shouldn't be influenced by this factor.
I think, then, that it makes the most sense to use highway=motorway for anything that meets the usual motorway criteria (specifically no at-grade intersections), highway=trunk for any road which allows relatively free travel (speed limit 50+, "few" lights), and highway=primary for any road which is "important" for moving traffic either through a city or between cities but doesn't have a high rate of flow (due to low speed limits or many traffic lights).
- It makes the normal OSM map very colorful.
- Better indication of the usefulness of a road for long-distance travel. Could help routers find the best route in absence of any actual speed measurements.
- US Highways which pass through small rural towns and become speed traps (i.e. sudden 35mph speed limit) probably would be highway=trunk outside the town and get marked highway=primary under this scheme, rather than trunk, thus providing a hint to drivers.
- If someone wants a map of the Interstate or US Highway system, they can still query the route relations and generate a map from that information.
- This could be done to generate a traditional "map of the US" where all the Interstates are one color and all the US highways are some other color, regardless of their actual traffic-carrying capacity.
BigPeteB 17:19, 13 October 2009 (UTC)
P.S. Regardless of what's decided on, this should really be consolidated into a single place.
I'm new to the project, so I've read all the documentation and the relevant commentary. What strikes me is that everyone, so far, is trying to map the OSM model to only a single view of reality. I do not mean this disparagingly, since, presumably, the ultimate goal is a model of the one world.
However, I suggest that there are three related but different aspects of our reality here in the US that we would consider:
I'll describe what I believe they are, as well as how I propose they factor into the OSM classification, with examples (mostly centered around where I live and work, naturally). I do not propose a rigid set of rules, but, rather, a framework on which to build ones best judgement.
This category includes anything that exists, fundamentally, on "paper" or as information. Sometimes, these aspects of a highway are, at their core, arbitrary.
Highway numbering, statutory classification, where the money for building and maintaining the road come from (including if it's a toll road), and traffic regulations are all Administrative.
I suppose a way to think about it is if one were the last human on earth, what attributes of a highway would no longer exist or be completely irrelevant?
There is an overlap with the "Practical" category in that highway numbers are not individually arbitrary and that we place them on signage. There is an inherent overlap in the area of traffic regulation. There is some overlap with engineering in certain regulations, such as with trucks.
Of course, none of us is the last person in existence, so administrative qualities of a road *do* exist and should be taken into account. The last traffic signal on the Interstate system was remove less than 20 years ago. Was that section still "motorway" (I would say no, it's not even a "trunk"). I-93 has a 2-lane section, exempt from Interstate standards, so how about this? (I would say yes, and it's definitely at least a "trunk").
Regardless of my opinion on these examples, my point is that merely calling something an "Interstate" doesn't supersede its engineering reality. Similarly, not calling a divided, multi-lane, limited access highway a "freeway" doesn't make it any less of one.
Today, bearing a US highway shield
On the other hand, absent any other clues, administrative classification, even if wishful or forward-looking, can be an excellent starting point.
This category ecompasses the physical attributes of the highway itself, many of which have their own tags. Most of these have to do with the construction of the highway, but some are aspects of maintenance.
- pavement material
- surface smoothness
- number of lanes
- banking of curves
- lane width
- pavement markers
- traffic control devices and the competence in their operation
- incline steepness
- local weather
- where built ("alignment")
The practical category might also be called the "end user" category, with both the user of the map and the highway itself to consider.
This includes branding and signage, such as "Interstate" and "Freeway" and highway numbers. It includes whether, despite access not being legally restricted, it is surrounded by (if I may borrow from Neal Stephenson's Snow Crash) burb-claves. It includes the typical traffic patterns of the local community.
Perhaps most importantly, it includes users' expectations. I suggest the principle of least surprise.
I would, for exmample, be surprised if a 4-lane street were classified as "residential," even if it were undivided, bore a residential street speed limit, and there were sidewalks only homes along the street.
I would not, however, be surprised if the difference between a trunk and a primary were less clear or nonexistent in another state.
I would also be surprised if any Interstate were not a "motorway," but I associate no such meaning with US highway branding. Other than the expectation that a 1 or 2 digit (plus US 101) such highway be contiguous and be mostly east-west if even, I have no expectations of them at all.
My Local Examples
In California, regulation is at the state level. However, most of the funding is at the county level. The construction of major highways is usually orchestrated by the state, but the maintenance and signage is done (differently) in/by each county.
Motorways are the easy classification, since that's freeways. The local outliers are the Golden Gate and Benicia bridges. They're freeways by statute, but not in engineering standards. They are both, however, directly connected to freeways, so it is, perhaps, a moot point.
For trunks, I think a good standard is "almost freeway except for one thing." This would apply to sections of divided rural highways which could be freeways except for at-grade crossings. These days it would reasonably apply to CA 17 over the Santa Cruz mountains.
The main question in my mind is if "trunk" applies to the Santa Clara county expressways and similar urban roads. They have mostly limited access, except where there are driveways directly into shopping areas. They have grade separation with railways, except in Milpitas. They have the fastest non-freeway speed limits of parallel roadways, except for San Tomas Expressway (45mph) and Brokaw Road (50mph until a year or so ago when San Jose re-signed it 45 mph). They have full interchanges with freeways they cross, except San Tomas and I-280. They have no uncontrolled at-grade crossings, except Oregon Expressway in Palo Alto. Still, I believe they were intended as trunks and the exceptions might one day fade, and if they're not an example of urban trunks, I'm not sure what is.
For primary/secondary/tertiary, I think the documentation is clear enough. I don't believe being a numbered highway is significant: Stevens Creek Boulevard is just as much a primary as CA 82 (El Camino Real or The Alameda). At the other end of the spectrum, I think there are very few urban "residential" roads here in th Bay Area, except for hilly areas and the streets within higher density burb-claves.
Mk408 18:47, 28 November 2009 (UTC)
- I've tagged several minor highways in Cincinnati as trunk highways, and they're pretty similar to the "urban trunks" you mention. For instance, Columbia Pkwy. (US 50) is very similar to Alma St. / Central Expwy. Vid the Kid and I have been pretty selective about tagging non–US routes as primary highways, non–state routes as secondary highways, etc. If Cincinnati had a state route like El Camino, I'd probably make it primary, but it wouldn't have much company. – Minh Nguyễn (talk, contribs) 07:53, 29 November 2009 (UTC)
- I agree on most points except where to anchor the lower end of the ladder. This is really about expectations, too. I think there is value in having a normal, average residential street be tagged "residential". And in the Bay Area, this means curbs, space for street parking and one lane in each direction. StellanL 13:02, 14 January 2010 (UTC)
Just to throw y'all a curve: In Texas, we have, on top of our state routes, "Farm-to-Market" and "Ranch-to-Market" highways (abbreviated "FM" or "RM", and sometimes referred to as "farm roads" and "ranch roads"), which serve exactly that: farms and ranches. There is one "beltway" that I'm aware of (Beltway 8 in Houston, aka "Sam Houston Tollway") and probably the one and only "Nasa Road 1" (near Galveston at the Johnson Space Center). There are even "park roads" for use in state parkland areas. Most of these are two-lane roads, but can easily be made into the other configurations. How would you classify all of these? --Rapierman 06:17, 31 October 2010 (UTC)