[Talk-us] Prima Facie Speed Limits

stevea steveaOSM at softworkers.com
Wed Sep 10 23:34:42 UTC 2014

Hello Kerry and Greg:

Even though I'm "just" a lay person in this regard, I'm rather 
familiar with the MUTCD (though not at the level of detail of a 
traffic engineer or a professional urban transportation planner).

Any "federal standard" about stop signs being red and eight sided and 
intersections being marked in consistent ways happens because of a 
well-understood scenario, envisioned by the authors of our federal 
Constitution:  states develop such things in an experimental way, 
some solutions are found to be more successful than others, and hence 
emerge, then other states pick up on working solutions and they 
implement them as well.  Sometimes (as with traffic engineering, the 
MUTCD and Interstate Highways), formal standards bodies (like AASHTO) 
craft such statewide standards into something which "resembles" a 
federal standard, but in fact are more like a broad understanding: 
states together coming to agreement independent of the federal 
government.  AASHTO, after all, is a non-profit of professionals, and 
while it is based in Washington, DC, it is not part of the federal 

I say this to underscore my original point:  the distinction between 
what is federal (only those "enumerated powers" specified in the 
Constitution), and what is state (everything else).  Much about this 
continues to be confused in the public mind, (a failure of good 
civics in our public schools?) but the basic facts of this haven't 
changed in over 200 years.  I don't want to get overtly political, 
but it does seem to bear repeating in this context.  Oh, and states 
accepting federal dollars doesn't "override" state's rights, states 
simply give away certain sovereign rights in exchange for the 
dollars.  They don't have to, but that IS the bargain.

In short, states are responsible for traffic laws.  There is some 
overlap between state and federal which has been deliberately crafted 
(Interstate Highways, ICE-TEA funding, MPOs usurping local control 
via federal $...), but the fact of state/local control over 
transportation infrastructure, law and funding remains essentially 
true, until something explicit (e.g. acceptance of federal $) changes 

I don't know what the answers might be regarding prima facie speed 
limits in OSM.  It doesn't seem totally incorrect to put these in, 
but again, I find speed limits in OSM most useful when they designate 
where a sign explicitly specifies what speed limits are where.  "Data 
consumers" (ETA algorithms...) may or may not use such data.  The 
"better" ones might pay attention to them, then use them or ignore 
them based upon even MORE intelligence.  Yet again:  conscientious 
attention to both structured data and code (logic) is warranted.


>Signage standards are contained in the MUTCD (Manual on Uniform 
>Traffic Control Devices).  These are standards, not absolute 
>requirements, but you will find them followed pretty closely because 
>traffic engineers don't like having to explain why they have not 
>complied with standards.  Several states have their own version of 
>the MUTCD, usually with either a few additions to the MUTCD or even 
>by reducing the options of signage.
>Kerry Irons
>From: Greg Morgan [mailto:dr.kludge.gm at gmail.com]
>Sent: Wednesday, September 10, 2014 9:22 AM
>To: stevea
>Cc: talk-us at openstreetmap.org
>Subject: Re: [Talk-us] Prima Facie Speed Limits
>I wonder if 15 mph in a school zone and 25 mph in a residential area 
>are some sort of federal standard?  The source tag might be useful 
>but not much different than other states.
>On Tue, Sep 9, 2014 at 10:31 AM, stevea 
><<mailto:steveaOSM at softworkers.com>steveaOSM at softworkers.com> wrote:
>The federal government doesn't have anything to say about speed 
>limits (in states), as the US Constitution leaves such things to the 
>I was thinking more like a stop sign is red and eight sided.  A 
>traffic engineer told me that there is a federal standard governing 
>how intersections are marked, etc.
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