Rjgambrel/To help discuss use of expressway=yes in Minnesota
The purpose of this page is to help facilitate a discussion in August 2022 about guidelines for using the expressway tag.
Background
Since the introduction of the expressway tag and the analysis of the tag's usage in Minnesota (in December 2012), guidance was provided for when the tag might be used for "motorway islands". No clear guidance was given, in general, as to when the tag should be used for other segments of highways that were not then considered motorway islands. This document is a survey of the guidance provided for when to use the tag in (1) Minnesota, (2) the US, (3) as described in the Expressway wiki page, and (4) in other states' highway classification projects. This page is provided to help enable discussion of what should be done in Minnesota to provide better guidance.
(1) Current guidance in the Minnesota Highway guidance page about Expressways
The general guidelines for using expressway=yes in Minnesota is quite simple and can be found in section 5.1.2. Section 5.2.2 also provides some specific guidance but only about one specific segment and several motorway islands.
Section 5.1.2 (Agreed guidelines/Tagging general guidelines/Expressways)
The US Highway reclassification page has a section mostly devoted to expressways titled Exceptions and Borderline Cases. The guidance provided there seems to apply well in Minnesota. Note that as of December 2021 the expressway=yes tag has only been used on a single highway segment for a total in Minnesota of 19.4 kilometers.
Minnesota will follow the US Guidelines for expressways.
Refer to the specific route by route proposals listed below.
Section 5.2.2 (Agreed guidelines/Route by route guidelines/Expressway detailed guidelines)
A highway segment currently (MN 60 between the Iowa border and Worthington) that is tagged with expressway=yes does not meet the criteria for being an expressway. Specifically there are numerous at grade intersections and there are no grade separated interchanges. The tagging should be removed. This step should be done prior to adding any new expressway tags. This tagging has been removed on 3/7/2022.
The following chart details specific places where expressway=yes should be used in Minnesota:
In the wiki page from which the above was pulled is "Table S3: Expressways" which is a list of previously analyzed motorway islands that should be changed to trunk/expressway. The only discussion in section 5.2.2 about non-island (i.e. general) usage of expressway is the first paragraph about MN 60. The remainder of this section focused on motorway islands.
(2) Current guidance in the US Highway Classification page about Expressways
On August 14, 2022 the use of expressway was mentioned as follows.
Section 2.1.1 (Classification/Motorway/Exceptions and Borderline Cases)
Highways listed in the Wikipedia article 
List of gaps in Interstate Highways should be tagged as follows:
- Highways listed with "major at-grade intersections" and "other at-grade intersections" should be downgraded to highway=trunk
- Highways listed under "movable bridges" should remain tagged as highway=motorway provided that the bridge-opening frequency is low enough that the motorway character and expectation of road users having priority isn't normally violated.
Roads which are disconnected from the motorway network, but briefly exhibit motorway-like characteristics for short distances (also known as "motorway islands"), should not be tagged as a motorway. In general, a disconnected motorway should have multiple grade-separated, controlled access interchanges over a significant distance, generally at least 2-10 miles, in order to be tagged as a motorway island.
Additionally, there exist a small number of examples of roads that are of an expressway character but have characteristics that are slightly degraded when compared to modern Interstate highway standards, and may have one or more features such as:
- Right-in right-out (RIRO) limited access ramps
- Short-radius access ramps
- Incidental surface land-access roads in rural areas
- High frequency of on/off-ramps
- Narrow lanes
- Lack of shoulders
- Low overhead clearance
- Brief sections of single-lane travel through tunnels or mountain passes
- Reduced speed limits
Because of the wide variety of urbanization character and highway construction quality throughout the United States, it is not possible to define a clear-cut rule for determining whether or not these borderline cases should be tagged highway=motorway or some lesser classification.
These borderline cases have been the subject of edit wars. As such, roads that are "borderline" as described above (motorway islands and slightly degraded expressways) must not be changed from their current classification without consultation with the community to determine whether a consensus exists. Changes to the classification of these edge case roads without community discussion may be summarily reverted.
Once consensus has been achieved on the tagging of specific corner case expressways, it should be documented on that state's wiki page, with a link to where the discussion took place. If the consensus decision is to tag the road as a lesser classification, tag them with expressway=yes, in addition to their base highway=* value. It is not necessary to tag a highway=motorway with expressway=yes, as this is presumed.
Section 2.2 (Classification/Trunk)
As the top non-motorway classification, highway=trunk should be applied in the following cases:
- In areas of high population density, to expressways that meet most, but not all, of the requirements for highway=motorway, and provide connectivity between motorways and other trunk roads. These roads should also be tagged expressway=yes.
- In areas of medium to low population density, to the most important non-motorway roads that provide principal, long-haul connections between population centers of regional importance.
Additional mentions of expressway
Section 5.4.1 says: Use expressway=yes on highway segments where it is appropriate.
(3) The Expressway Key
The "official" wiki page for Expressway contains a lot of information that might inform us how to move forward in Minnesota.
Some possibly useful statements regarding requirements for using the tag are:
1) a highway that is designed for high-speed travel but lacks some of the characteristics that enable a motorway (freeway,
highway=motorway) to accommodate a high volume of high-speed traffic safely.
2) In general, an expressway overall:
- is a dual carriageway (divided highway,
dual_carriageway=yes)- has a higher than usual speed limit and accompanying design features, such as motorway-style signage
- has limited access to abutting properties (
access_control=partial), for example via frontage roads and right-in/right-out intersections
3) may have at-grade intersections with other public roads
4) an expressway typically restricts access to slower modes of transportation, such as pedestrians (
foot=*) and cyclists (bicycle=*).
5) the Highway Performance Monitoring System defines an expressway as:
- A divided highway facility with partial control of access and two or more lanes for the exclusive use of through traffic in each direction; includes grade separations at most major intersections.
6) Regional variation in road design can also be a deciding factor. True expressways are rare in the northeast United States
7)
expressway=yescan also refer to a "Jersey freeway", which is a divided road (typically a jersey barrier and narrow overall footprint) with high-speed design and grade separations. Unlike a standard expressway, however, it does have frequent access to adjacent properties, but has few or no at-grade intersections with other public roads.
(4) Current guidance in other states' guidance pages
Other states take different approaches (from Minnesota and each other) in dealing with expressways. A quick look for "expressway" in the various state specific pages found this rough breakdown. (Apologies to other states if I have mischaracterized or mis-counted in my quick cursory survey.)
| Number of States | Characterization of handling of expressway tag |
|---|---|
| 20 | No row in the state-specific classification standards table |
| 14 | Either no wiki page or no references to the expressway tag |
| 1 | Competing proposals; did not inspect either |
| 6 | Provide specific guidance about specific highway segments but provide no general guidance |
| 9 | Provide at least some general guidance about when to use the expressway tag |
The 8 other states (in addition to Minnesota) that provide some general guidance may be useful in informing Minnesota decision making on whether the Minnesota guidance should be changed. These states are:
- California
- Colorado
- Nebraska
- New Hampshire
- New Mexico
- Oklahoma
- Vermont
- Virginia
Usage of the tag as of this writing (in Minnesota)
This chart gives the current status of how the expressway tag is used in Minnesota. The usage of the tag was also measured in December 2021 near the beginning of the Minnesota Highway classification effort. Clearly the usage of the expressway tag has increased greatly during 2021.
| Expressway= | 2021-12-24 | 2022-08-20 |
|---|---|---|
| yes | 19.4 | 178.0 |
| no | 594.0 |
Much of the "no" was done my me, aggressively interpreting the US guidance (I keyed off the phrase: "slightly degraded"). Some segments might be reverted to "yes" after this discussion, as might some of the "yes" segments be changed to "no". Additionally, some segments (not measured or currently measurable) of motorways also had expressway tagged as yes. When found the expressway tag was removed (as redundant). Use of expressway=yes for them was not wrong, but just not needed.
I have paused my expressway related mapping changes until this discussion plays out.
Summary list of the criterion found in all of the sources above
The following table summarizes the criteria specified by the various documents surveyed. The first column identifies the source pages (corresponds to sections 1 through 4 above). An ID is assigned to each criterion line to make discussion simpler. The third column purpose and values are described below the main table. Please refer to that small key before spending much time understanding this criterion chart. Note that some words have been capitalized by the author to emphasize quantitative guidance such as "most" or "some"
| Source | ID | Expressway? | Criterion |
|---|---|---|---|
| MN | MN-1 | Minnesota will follow the US Guidelines for Expressways | |
| MN-2 | no | Segments that have no grade-separated interchanges | |
| MN-3 | no | Segments that have numerous at-grade intersections | |
| US | US-1 | yes | Have characteristics that are slightly degraded (see 1a-1i) |
| US-1a | allowed | RIRO limited access ramps | |
| US-1b | allowed | Short-radius access ramps | |
| US-1c | allowed | Incidental surface land-access roads in rural areas | |
| US-1d | allowed | High frequency of on/off ramps | |
| US-1e | allowed | Narrow lanes | |
| US-1f | allowed | Lack of shoulders | |
| US-1g | allowed | Low overhead clearance | |
| US-1h | allowed | Brief sections of single-lane travel through tunnels or mountain passes | |
| US-1i | allowed | Reduced speed limits | |
| US-2 | yes | In high population density areas, if a segment meets MOST BUT NOT ALL of the requirements for motorway, AND provide connectivity between motorways and other trunk roads, tag as trunk and expressway | |
| Key | Key-1 | yes | Designed for high-speed travel but LACKS SOME of the characteristic of a motorway |
| Key-2a | yes | Is a dual carriageway (dual_carriageway=yes) | |
| Key-2b | yes | Has higher than usual speed limit and acompanying design features, such as motorway-style signage | |
| Key-2c | yes | Has limited access to abutting properties (e.g. via frontage roads and RIRO intersections) | |
| Key-3 | allowed | May have at-grade intersections with other public roads | |
| Key-4 | allowed | Typically restricts access to slower modes of transportation (e.g. pedestrians and cyclists) | |
| Key-5 | yes | A divided highway facility with partial control of access with 2 or more lanes for exclusive use of through traffic in each direction; includes grade separations at MOST major intersections | |
| Key-6 | Regional variation in road design can also be a deciding factor. | ||
| Key-7 | yes | A "Jersey freeway": divided (typically with Jersey barrier and narrow overall footprint) with high-speed design and grade separation. May have frequent access to adjacent properties but has few or no at-grade intersections with other public roads | |
| Others States | Others-1 | allowed | There may be cause for expressways in rural areas that do not have any grade separated intersections due to lack of significant intersections or traffic levels |
| Others-2 | no | If a trunk road does not meet the standards of expressway (such as a super 2 or within an urban area where the median may be removed in favor of a center lane) | |
| Others-3 | Having "expressway" in a highways name does not automatically make it an OSM expressway | ||
| Others-4 | There are no requirements for expressways to be networked (as it is more of a rendering tool than a routing tool) | ||
| Others-5 | yes | Roadways that meet SOME, BUT NOT ALL the cirteria of motorway. Should add access_control=partial. | |
| Others-6 | yes | In cities & towns: business access by frontage road only | |
| Others-7 | no | Use expressway=no for trunk highways that are not expressway=yes | |
| Others-8 | yes | In high population density areas: meets MOST BUT NOT ALL requirements of motorway AND provides connectivity between motorways and other trunk roads | |
| Others-9 | yes | Do not meet ALL of the criteria for motorway, but are more efficient roads than most others. |
The possible values in the third column are described in the following small chart:
| table entry | meaning |
|---|---|
| yes | the criterion specifies that expressway=yes is appropriate |
| no | the criterion specifies that expressway=no is appropriate |
| allowed | the criterion is an attribute that is allowed if expressway=yes |
| <blank> | interesting statement that does not provide clear tagging guidance |