From what i have read of the Manual on Uniform Traffic Control Devices (MUTCD) This is true.
http://mutcd.fhwa.dot.gov
1) Page 1A-16 section 24, An engineering study shall be conducted by an
engineer to determine the appropriate speed limits and traffic controls and
this study shall be documented.
2) Page 2B-13 section 2B.11 The posted speed limit shall be in accordance
with the engineering study and shall be posted at the 85th percentile speed
of free flowing traffic rounded up to the nearest 5mph increment.
3) Page 1A-6 section 1A.10 Adoptions of traffic control devices other than
as described in this manual are prohibited.
4) Page 1A-6 section 1A.09 Jurisdictions without engineers on staff must
seek assistance from engineering consultants or nearby jurisdictions with
qualified engineers on staff, or the State Transportation Agency.
5) Page 1A-4 section 1A.07 When any local or State jurisdiction uses any
manual or supplement for determining traffic controls, that manual or
supplement must conform to the MUTCD.
6) Page 1-1 introduction: Standard, Paragraph 2: The MUTCD is authorized by
23 Code of Federal Regulations (CFR), part 655, Subpart F and is the
national standard for all traffic control devices on all public roads in
accordance with 23 U.S.C. 109(d) and 402(a). These are the policies of the
Federal Highway Administration (FHWA) to obtain basic uniformity of traffic
control devices as described.
Reference #1 means that an engineering study (speed survey) is not optional
if a speed limit is to be posted and enforced. It must be done. It must be
done by an engineer, and the survey must be documented and therefore
available to the public. This is obviously so that agencies can't just
create false low speed limits (speed traps) and then milk the public for all
the money they want in illegal revenue.
Reference #2 means that part of every legal engineering study is to
determine the 85th percentile speed, or the speed of the average driver,
then the road which was surveyed must be posted at that presumptively safe
85th percentile speed rounded up to the nearest 5mph.
Reference #3 means cities and towns
can not choose to obey or not obey these
Federal regulations
Reference #4 means that small towns or any agency that does not have or
cannot afford a traffic engineer (not just a job title, but someone with a
traffic engineering degree) must hire an engineering firm or arrange for an
out of town engineer to conduct the traffic engineering studied. Small towns
are never exempt from compliance with every regulation of the MUTCD.
Reference #5 means that cities, counties and towns cannot create thier own
manual or supplemental or municipal codes and say "we go by our own little
book". The only way a city can follow any other publication no matter the
source is if that publication conforms to the MUTCD. There are a couple of
states that use thier own book and usually call it the "State Traffic
Manual". However, as in the above federal reference, these books are legal
only as long as they conform to the MUTCD. Why do they print them, you ask?
Usually to try and bend the federal regulations and claim that it is ok,
because it is authorized in their own book. Remember, Federal superceeds the
State. Anywhere they differ, the State book is in error. In other words they
have to follow the federal regulations period.
Reference #6 gives the federal code book references that any judge or police
officer can look up as well as the references given from the MUTCD, and see
that the MUTCD is the bible of traffic law and traffic enforcement. There is
no other book that superceeds the MUTCD. The MUTCD superceeds all other
publications in regard to traffic controls and enforcement.
I could be wrong here, am I?