[Talk-us] Speed Limit Validity in US Questions

Sat Jul 3 10:55:02 UTC 2021

Vào lúc 07:42 2021-07-02, Horea Meleg đã viết:
> 1. A speed limit sign is valid until next intersection, or until next speed limit sign encountered?

The national MUTCD standard calls for a speed limit sign to be posted at 
each point where the speed limit changes and, optionally, a confirmation 
sign posted after major intersections and at an interval along the road. 
[1] (Most states have their own MUTCD editions or supplements instead of 
following the national standard verbatim. The California [2], Delaware 
[3], Indiana [4], Maryland [5], Michigan [6], Minnesota [7], Missouri 
[8], Ohio [9], Texas [10], and Utah [11] MUTCDs largely follow the 
national MUTCD with regard to speed limit signs.) The spacing of 
confirmation speed limit signs depends on the state, road 
classification, and speed limit. [12][13]

Many states have guidelines to the effect of: if the speed limit changes 
at or just before an intersection, then the speed limit sign is the 
first sign posted just beyond the intersection. [5][14][15] Therefore, 
the sign's exact location is not necessarily the precise location where 
you'd split the roadway. In practice, if a north-south road has a 
different speed limit sign to the north of the intersection when going 
northbound and to the south of the intersection when going southbound, 
you'd typically split the roadway at the intersection instead of tagging 
a several-yard-long segment with maxspeed:forward/:backward tags.

As long as you're following a single road and aren't turning off onto 
another road, you can pretty much count on seeing a sign of some sort 
around where the speed limit changes. If there's even such a thing as an 
"until the next intersection" speed limit, the sign would say so. The 
closest exception I can think of would be a school zone speed limit: 
some states explicitly post a sign where the school zone ends, while 
others do not. In the latter case, you could try locating the beginning 
of the school zone on the other side of the road.

Rarely, a solid white line painted across the roadway can indicate a 
change in speed limit or the beginning of a school zone. [16] This would 
be the exact place to split the roadway.

> 2. If it's until next intersection, which is considered as intersection? Any kind of highway type? Or there are some special rules?
> 
> For example:
> 
> A.	   T intersection it’s considered?
> B.	   Cross intersection it’s considered?
> 
>   
> 
>    - I'm asking this because for example in Europe there are both situations (next sign vs next intersection) depending on country rules.

As noted above, a speed limit doesn't implicitly revert to another speed 
limit as you pass an intersection. However, it is common to post a 
confirmation speed limit sign at "major" intersections. Most standards 
are vague about what qualifies as a major intersection. Some states say 
it's based on the cross street's traffic volume but don't say how much 
traffic volume the street needs to carry to qualify. Georgia considers 
every intersection with a U.S. or state route to be major. [17] 
T-intersections and four-way intersections wouldi probably be treated 
the same for the purpose of speed limit sign placement.

> 3.  Speed Limits marked on the road are considered as valid, or just those posted on a traffic sign? Meaning it could be added the information in OSM based on speed limit road markings?

The national MUTCD allows for a pavement marking to supplement a speed 
limit sign. [18] These markings are the norm in urban and suburban areas 
in California. Elsewhere, they're much rarer, only used where there's a 
drastic speed reduction. They're just about always accompanied by speed 
limit signs, so if you see a speed limit pavement marking in aerial 
imagery, feel free to use it as a source, but don't count on there being 
another pavement marking at the end of the speed zone.

As others have noted, in some jurisdictions, it's quite common for a 
speed limit to go unposted anywhere along a given street, so the default 
speed limit takes effect. The MUTCD allows a jurisdiction to post a 
default speed limit at the boundary, applying to any street that doesn't 
have an explicit sign. Default speed limit signs are common, for 
example, among cities and villages in Ohio and in various neighborhoods 
of New York City.

A minor road may have no speed limit sign in a rural area that has no 
default speed limit sign. In the absence of any sign, determining the 
default speed limit is a maddening exercise [19][20], so I would advise 
your team to obtain an authoritative dataset from a state transportation 
department or county engineer's office as a reference or ask local 
mappers to research it for you, rather than making any assumptions 
yourselves.

[1] https://mutcd.fhwa.dot.gov/htm/2009/part2/part2b.htm#section2B13_para03
[2] 
https://dot.ca.gov/-/media/dot-media/programs/safety-programs/documents/ca-mutcd/rev6/camutcd2014-part2-rev6.pdf#page=36
[3] 
https://regulations.delaware.gov/register/may2018/final/MUTCDPart2Signs.pdf#page=38
[4] 
https://www.in.gov/dot/div/contracts/design/mutcd/2011rev1/part2b.pdf#page=12
[5] https://www.roads.maryland.gov/mmutcd/2011_Chapters_02B.pdf#page=19
[6] 
https://mdotjboss.state.mi.us/TSSD/getTSDocument.htm?docGuid=a933ceab-0a6c-4c81-a7fa-c3d973b002a5&fileName=mmutcdpart2b_2017.pdf#page=12
[7] 
https://www.dot.state.mn.us/trafficeng/publ/mutcd/mnmutcd2020/mnmutcd-2b.pdf#page=18
[8] 
https://epg.modot.org/index.php/903.5_Regulatory_Signs#903.5.10_Location_of_Speed_Limit_Signs
[9] 
https://www.dot.state.oh.us/Divisions/Engineering/Roadway/DesignStandards/traffic/OhioMUTCD/Documents/2012%20OMUTCD%20-%20Pt.%202.pdf#page=36
[10] 
https://ftp.txdot.gov/pub/txdot-info/trf/tmutcd/2011-rev-2/2b.pdf#page=13
[11] 
https://drive.google.com/file/d/1JyNnvMXo5LgvhvSltSOh5miCxD84PSdJ/view 
page 56
[12] 
https://ncutcd.org/wp-content/uploads/meetings/2011A/Attach-7-RW-No.6-Spacing-of-Speed-Limit-Signs-Appvd.pdf
[13] 
https://safety.fhwa.dot.gov/speedmgt/ref_mats/fhwasa1304/resources2/22%20-%20Policy%20on%20Establishing%20and%20Posting%20Speed%20Limits%20on%20the%20State%20Highway%20System.pdf#page=6
[14] 
https://www.wsdot.wa.gov/publications/manuals/fulltext/M51-02/Chapter2.pdf#page=14
[15] https://cornell.app.box.com/v/clrp-pb-tsh page 88
[16] 
https://www.bing.com/maps?osid=b9ea6558-8009-4b1b-9aea-595fc6769446&cp=32.829231~-97.188199&lvl=19&dir=0.337&pi=0&style=x&mo=z.0&v=2&sV=2&form=S00027
[17] 
http://www.dot.ga.gov/PartnerSmart/DesignManuals/smguide/GDOT%20SIGNING%20AND%20MARKING%20DESIGN%20GUIDELINES.pdf#page=25
[18] https://mutcd.fhwa.dot.gov/htm/2009/part3/part3b.htm#section3B20
[19] https://wiki.openstreetmap.org/wiki/Default_speed_limits is heavily 
abridged, but it gives a sense of the complexity involved.
[20] https://commons.wikimedia.org/wiki/File:Speed_limits_in_Ohio.svg is 
also abridged but is already quite complex.

-- 
minh at nguyen.cincinnati.oh.us