County of Cass V. Floyd L. Phillips - MEMORANDUM ATTACHMENT



Laws protect the public by regulating unreasonable or unsafe actions. Actions of a reasonable person should be legal. Most people drive in a safe and reasonable manner. Laws cannot be effectively enforced without the public consent and voluntary compliance. Laws give highway agencies or localities authority to post limits (higher or lower), if they are determined on the basis of engineering study and accordingly, that they be fair, be related to risk, be credible and accepted by drivers and enforce control over unreasonable behavior.

For a state or local posted speed limit to be lawfully established, the numeric value displayed on this federally regulated traffic control device (federal designation, R2-1) must have been determined in accordance with the conditions precedent specified in Title 23, United States Code, Section 109(d) and Title 23, Code of Federal Regulations, Part 655.601 through 655.603; which specifies mandatory compliance with the Standards in the National Manual on Uniform Traffic Control Devices (MUTCD); the Supremacy clause provision under Article IV, Section 2 of the U.S. Constitution, providing that federal law is superior to and overrides state law when they conflict; and due process under the U.S. Constitution. The second paragraph of the federal standard below clearly states “regardless of type or class or the governmental agency having jurisdiction”.

MUTCD, 1A-2 - Requirements of Traffic Control Devices
This Manual sets forth the basic principles that govern the design and usage of traffic control devices. These principles appear throughout the text in discussions of the devices to which they apply, and it is important that they be given primary consideration in the selection and application of each device.

The Manual presents traffic control device standards for all streets and highways open to public travel regardless of type or class or the governmental agency having jurisdiction. Where a device is intended for limited application only, or for a specific system, the text specifies the restrictions on its use.

Numeric value that speeds-in-excess-of represents an unacceptable hazard to others as determined by a site specific “Basis in Fact” engineering finding.

*Absolute limits are warranted in school, alleys, construction and hospital zones or other such areas where high pedestrian traffic, etc.. However, absolute and special speed zones shall only be in effect after the numeric displayed has been determined by a site specific engineering finding of fact and be in effect only during specific times of day when the hazard is present, and removed or covered immediately when the hazard ceases to exist.

A federally regulated “Regulatory Traffic Control Device” (R2) that local and state authorities are granted a “conditional use permit” to post on any roadway open to the public, conditional on full compliance with the mandated “conditions precedent” contained in the National MUTCD (Manual on Uniform Traffic Control Devices).

MUTCD section 2B-10 requires that the numeric value be determined on basis of an engineering study finding that determined a need exist for that particular section of highway. To wit, review of roadway”s prevailing speeds, highway conditions, hazards and accident history – determining if the use of this mitigation device is justified, if so, then report on what numeric values are authorized within the guidelines to post. Once determined, the political entity can choose between those options that have been identified appropriate for that particular section of roadway.

There is no engineering requirement to post a speed limit. In fact, the opposite is true. The MUTCD admonishes that devices only be used when warranted and when they would have the desired effect on reducing accidents. The MUTCD states, “A standard device used where it is not appropriate is as objectionable as a nonstandard device; in fact, this may be worse, in that such misuse may result in disrespect at those locations where the device is needed.” The MUTCD also recognizes urban and rural conditions may require different determination criteria.

After the repeal of the NMSL speed limit, legislators wrongly assumed this was a political decision that they were to decide. The prior existing and extant laws of the land granted no such authority whatsoever to post an invented statutory numeric on these official traffic control device. Paper on this issue: 1966 Law Best Guide for 21st Century, Safety and Setting Speed Limits

Periodic traffic engineering studies are required on all roadways - even on roadways without speed limits. The measurement of speed in a traffic engineering study is only one component of an extremely important periodic safety evaluation of a particular section of highway.

When this information is combined with the accident history for that section of highway the engineer has the information needed to determine what mitigation efforts may be required to address the identified safety hazards and flow management issues and needs for that section of roadway. The measured prevailing speed of traffic determines the size and the distances for all traffic control devices and where they need to be placed to accomplish intended desired action, the timing of traffic lights, the length and capacity of turn lanes, the type of signs that may be warranted to guide traffic or warn traffic in advance of hazards that aren”t readily apparent to the approaching motorists et al.

This federal law is an ironic twist on federal government preemption. The drafters knew that safety is best served when the actual road being regulated is reviewed taking into account all factors. Traffic engineering studies become the cornerstone basis-in-fact finding as to what traffic control devices or safety mitigation may be warranted. Because, without a study, all traffic control is based on unfounded conjecture and safety is compromised.

Federal law says according to LOCAL conditions, after engineers have personally determined how the people who use that particular section of highway are driving and they have reviewed the highway facilities, existing traffic control devices and accident data. Then they are directed to apply nationally accepted and verified sound engineering practices to remedy any problems and best manage the flow for the conditions found - not conjecture from Washington, State Capitals or Local Politicians.

MUTCD: 2B-10 Speed Limit Sign (R2-1) "The Speed Limit sign shall display the limit established by law, or by regulation, after an engineering and traffic investigation has been made in accordance with established traffic engineering practices. The speed limits shown shall be in multiples of 5 miles per hour." Accepted practices: "Established traffic engineering practices" are those practices that are nationally recognized and have a substantiated basis in fact. Nationally recognized: The engineer must be able to articulate what studies or

FHWA, ITE or ASSHTO recognized guidelines, standards or studies that this basis-in-fact finding is based on. Interstates and surface highways each have their own different studies, standards and practices. The authority ordering the placement of the regulated devices must be applying nationally recognized practices. If there is no staff personnel that understand these mandates and procedures, then the MUTCD advises them to consult with outside experts or engineers from other agencies.

The use of the term "Engineering Judgement" is not a license authorizing the use of unapproved or hypothetical unverified methods, unfounded conjecture or to carry out personal or collective beliefs. There is a forum to ask for a variance from nationally accepted practices if the posting authority believes they have a better answer or method, but the National Committee must approve this thesis prior to field trials or test. A "Basis in Fact" finding can not be made without a site specific review/study that includes a detailed review of the above factors that are applicable for the particular section of roadway being regulated. Items to be reviewed are different for different classes and types of urban and rural highways, but site specific studies are required to justify the use first, then what particular devices are indicated and where the would be most effective and then the numeric value assigned must be supported and germane to accident reduction at that location.

Posting for curves or hidden hazards is to be done with advisory warning devices and downward posting for those conditions already apparent is not advised. Speed limits are posted for the free-flowing higher prevailing speed sections. Curves and hazards are to be posted with advisory warnings in proportion to the danger they represent to the approaching motorists travelling at the prevailing speeds – at sufficient distance to timely advise the motorists of the degree and nature of the approaching hazards.

California Vehicle Code states the anti-downward zoning rationale well:

VC 22358.5 "It is the intent of the Legislature that physical conditions such as width, curvature, grade and surface conditions, or any other condition readily apparent to a driver, in the absence of other factors, would not require special downward speed zoning, as the basic rule of section 22350 is sufficient regulation as to such conditions."

These practices are already being certified as being done in exchange for federal highway funds being received by the state. Nevertheless, many highway agencies and localities claim it would be too great a burden to actually comply with the law.

It is not a burden on the agencies. It is rather a choice made in the allocation of resources by the posting authority. For a proper study to be done on a cross-town expressway. As an example, it may take several man hour weeks once every 5 years. On the other hand, there has been no shortage of man hours available for enforcement with multiple officers assigned to work an area, frequently on a daily basis, resulting in many man hour years being allocated over this same 5 year period for enforcement of limits not lawfully set.

By far the most effective use of funds have been the investments made in engineering reviews along with mitigation efforts to guide and facilitate traffic by reducing flow conflicts and removing hazards. This is the primary function of an engineering study and the data collected to verify the appropriate speed limit posting is only one component of this necessary safety review program.

Free-flowing or Free-moving according the FHWA specifications is a minimum 4 second unencumbered headway between vehicles. Taken at representative higher speed free-flowing sections of the roadway being studied. Speed measurement locations should not be encumbered or under the influence of intersections, curves (horizontal or vertical), lane reduction zones, hazard warnings, traffic signals or stop signs.. i.e. choke points in measured speeds or flow conflict points. Minimum 500’ distance is required from a flow obstruction to the location where the speeds are measured.

The lead vehicle in a queue skews down results by unduly influencing the following vehicles natural pace speeds. Therefore, all vehicles in queues are not to be counted because the lead vehicle has biased down speeds all those that follow. If you count the lead vehicle and not the others in the queue you bias down the speed proportional by the number of vehicles whose higher speeds would have been measured if the slower vehicle had not impeded their movement. The intent of the speed measurements is to determine the actual speed of the unimpeded free flowing traffic. The speed of traffic should not be altered by concentrated law enforcement, or other means, just prior to, or while taking the speed measurements.

Defined as that speed at or below which 85 percent of the traffic is moving. On urban roadways the 85th percentile speed has been found to be the safest speed, where the 85th exceeds 50 mph the safest speed shifts to the 90th percentile. Speed limits established on the basis of the 85th percentile on urban roadways conform to the consensus of those who drive highways as to what speed is reasonable and prudent, and are not dependent on the judgement of one or a few individuals.

On most high volume roads, the recommendation is the 85th rounded up to the next 5 mph increment. Some jurisdictions it is the 85th rounded to the closest 5 mph increment and in school or residential districts it is the 85th percentile lowered to next 5 mph increment.

California’s appellant courts have defined unreasonably low, from a public safety standpoint in applying engineering standards, as any posting below the 85th lowered to the next 5 mph increment unless there were well documented exceptions. Hazards that are readily apparent to the motorists are not justifications as they are already reflected in the motorists actions. Regardless of justification, no posting below the next 5 mph increment is acceptable.

Likewise, the ITE 4M-25 Committee on Speed Limits found that in no case on the high volume roadways should the speed limit be set below the 67th percentile speed of free flowing vehicles.

California courts have adjudicated thoroughly what constitutes a justified study on urban streets and secondary highways as well as what rights a defendant has in challenging the numeric posted. The 85th percentile speed is the primary consideration. In the following cases the defendants challenged the validity of it findings. The court ruled in the defendant”s favor that the study was inadequate. People v. Ellis, (1995) 33 Cal. App, 4th 525

"Since the summary contained none of the raw data collected during the survey, how could the defendant have shown that the survey was inadequate?" "Allowing a defendant to attack the adequacy of an engineering and traffic survey if the document is not available for his or her use at trial."

Superior Court of the State of California, for the County of Ventura, Appellate Department, case no.: 13 Cal, App.4th Supp. I 1992 the People vs. Goulet. (attached) Conclusion;

"The survey in this case did not justify the prima facie speed limit."

The traffic engineer’s speed survey is simply a measurement of the "public’s consensus" as to what free-flowing speed they have found to be safe. Each motorist drives at a speed they feel comfortable and safe with. Each driver expresses their comfort level by their actions, taking in to account all visual clues that may be present. Engineers have found this to be a better process than basing the speed limits on the arbitrary judgments of a few. Setting all traffic control devices, turn lane lengths etc. based on this measured public consensus has been the most effective in reducing accident rates.

There are 2 types and applications of the term design speed within the traffic engineering profession. This has created considerable confusion for those not familiar with these distinctions and how they are applied.

Design Speed of Highway: Was first defined in the 1940’s as a comfort standard. During the Eisenhower administration in the mid 1950’s, the target design speed for the new National Defense Interstate Highway system was 70 mph. Example of comfort application; The desired design speed of a curve was the minimum 70 mph speed. This standard was represented in a formula that combined both the minimum radii and banking required to accomplish this comfort goal.

It was expressed in terms of lateral G force generated by the curve. A lateral force great enough to feel discomfort for an unseatbelted person sitting on the passenger side bench seat of a 1940’s motor vehicle. Discomfort - effort required to maintain their seating posture comfortably. Generally this G force was between .1 and .15 Gs.

Design Speed of Traffic Control and Safety Mitigation Devices: There is only one accepted method of making this component’s determination and it based on actual engineering study of the particular section of highway under review, if it is already open to the public. Or, if it is new construction, by applying the findings from a like section of highway where studies have been done – and after opening it to the public, doing a review to make sure the assumptions were correct.

Safety is comprised when these procedures and practices are not followed. Without the study all traffic control, management, guidance and safety countermeasures are based purely on conjecture.

By measuring the actual free-flowing prevailing speed and looking at these trends, the engineer has a basis in fact starting point as to what the design speed specifications should be for all the devices to be installed on that particular section of highway. The design speed determines the specification for size and type of all devices used and installation distance from point of need - Signs, exit designs, impact attenuators etc.

On the face of it, virtually all Department of Transportation are now violating these principles on Interstate highways. Most proclaim current design speeds of 70 mph or in accordance with legislature established unlawful state statutory limits. Both reasons violates basic engineering tenets because it is of common knowledge that the current prevailing free-flowing speeds of traffic is exceeding this design specification and that traffic speeds only increase over time and it is a natural process of advancing technology. Therefore, safety has been and is continuing to be compromised.

Accepted: Loops or imbedded magnetometers are always preferred, then comes dual rubber hoses and devices like the Nu-Metrics Trans Star 9700 which is a small computer that is temporally anchored to the pavement. The software for all these programs can produce vehicle speeds, classifications and headway.

Radar and Laser Not Advised: As long ago as the late 70’s the FHWA found that states using radar to measure speeds for compliance with the National Speed Limit were showing measurably better compliance than those states using traffic loops. They immediately outlawed the use of radar to collect data in compliance reports, because of radar detectors and even unmarked vehicles parked on the shoulder were documented to result in lower than actual reported speeds.

The study shall include a report on the number and nature of accident for that particular section of roadway. The engineer should compare this with an on site analysis of the location looking at all contributing roadway design, delineation and traffic control device factors present.

Most recognized statutory time: ITE guidelines state that all highways should have safety reviews at least once every 5 years and this includes an engineering study of current traffic patterns and accident data.

Exceptions: Anytime development or highway work has been done in area which substantively changes the conditions on that particular section of roadway. To wit, where changes in roadway or traffic conditions have occurred, including, but not limited to, changes in adjoining property or land use, roadway width, or traffic volume. Example: simply resurfacing a highway without other changes can result in increased measured 85th percentile speeds up to 4-6 mph.

You want to minimize speed limit changes by averaging the findings on contiguous sections of highway to post uniform speed limits. If the posted limit does not exceed a plus or minus 5 mph posting recommendation for this section, averaging is warranted. If the speeds show an incremental increase in a particular direction then post the limits accordingly. The FHWA workshops recommended measurements be taken every 1/2 mile for local roadways. On Interstates there should be sufficient measurement points to get a true picture of the prevailing speeds.

The legacy of the NMSL left us with few government personnel aware of prior law or understanding of its principles and mandates or knowledge of how to set interstate limits. Information on procedures is sparse and there are many misconceptions prevalent, even among engineers.

There has only been a few comprehensive studies of urban interstates, Cirillo’s speed relative risk curve became the accepted baseline. (Cirillo, J.A., Interstate System Accident Research Study II, Interim Report II, Public Roads, Vol. 35, No. 3, August 1968, pp. 71-75)

There is a direct correlation between accident rates and flow conflict points; converging highways and interchanges. The accident rates at these locations are primarily a design question regarding methods used to allow traffic to egress and ingress into the stream or converge. If they are too close to each other rates increase exponentially. Once the stream clears these conflict points the accident rates drop precipitously.

The speed of traffic is self-regulating, flow becomes uniform as congestion increases and the speed of traffic in not effected or influenced by posted speed limits nor are the nature and type of accidents that do occur. Conversely, when the conditions become light, you do see increases in speed differentials and during these light free-flowing periods” accidents for any reason drop to negligible rates.

The shape of the Cirillo curve was heavily influenced by the accident rates of vehicles that had slowed, or were traveling slower than the mean, and those traveling in the lanes closest to flow conflict areas. The nexus of this study was a widely held thesis that speed differential was a major contributor to accident rates on urban interstates.

When read, the studies data clearly shows that vehicles traveling well above the mean have the lowest accident rates and once motorists clear the conflict points, accident rates are negligible for any reason.

The safest speed - the mean plus 12 mph were the least likely to be involved in an accident and until you exceeded the mean plus 18 mph did the higher speed vehicles reach the risk of those traveling at the mean or slower.

When site data is examined and only those accidents during the light free-flowing periods away from the conflict points are analyzed, flow differential accidents are extremely rare events and the Montana and Autobahn experience quantify in real world experience that speed limits on this classification of highway have little or no effect during off peak hours.

On what values should be primary consideration, at FHWA workshops they handed out copies an Indiana study. Prior to the national speed limit being adopted, there was a debate going on within the engineering community as to what was the most appropriate value to set urban interstate limits at. (Maximum Speed Limits: A Study for the Selection of Maximum Speed Limits, Indiana University, Institute of Research in Public Safety, final report, volume I, Oct. 1970, Contract No. FH-11-7275)

This Indiana study evaluated between the 2 choices being championed by different factions of the engineering community. It examined if it should be the 85th or the 90th percentile of free-flowing traffic speeds rounded up to the next 5 mph increment. On urban interstates the study concluded it should be the 85th percentile rounded up.

If speed limits are found to be warranted for urban Interstates, it must be noted that when the Cirillo relative risk curve is overlaid on actual speed data, the safe for conditions speed at these location extends up to and includes the 95th percentile and more.


The most accepted and only verified method of setting speed limits on urban interstates is found in the 1970 Indiana study’s findings, limits on urban freeways should be set at the 85th rounded up to the next 5-mph increment.

There are no studies on contemporary Rural Interstates and Primary highways for anyone to use as a baseline or to refer to make a judgment from. In this vane Montana’s DOT undertook many different evaluations to determine if there were cause and effect relationships to accidents. They studied the origin of the vehicle registration and speed to see if there was a correlating accident cause and to determine which group had the highest speed. This honor went to vehicles registered in Alberta and Washington State; they were not over represented in the accident data. The following is the conclusion of the author based on what evidence was made available and the accident data supports these observations. A review of the Montana data can be found at - 2/01/00 Final Report: Montana – No Speed Limit Safety Paradox
found at:

The 85th percentile is not a sound basis to determine these limits. The evidence provided by Montana’s experience would suggest that speed limits have no effect on fatality or incapacitating injury rates for this class of roadway. If speed limits are to be set then they should be set to encompass all those vehicles found on the relative risk curve to be a low risk for being in an accident.

Applying numbers to the most accredited relative risk bell curve, by Cirillo, tells an interesting story. This curve was based on urban interstate research during off peak hours. It found the safest speed to be the mean plus 12 mph, and when charted on the graph the safest speeds extended up to the mean plus 18-20 mph.

Translated, the current mean on most rural interstates is between 70-75 mph and the safest speed would be 82-87 and the vehicles least likely to be involved in an accident are those traveling between 70 and 93-95 mph. The current speed limits are set so low that the vehicles least likely to be involved in an accident, according to the studies, are the primary targets of enforcement during the best highway conditions.

Should the limit be set at 90 or 95 mph? Either way, it would seem to have no effect on accident rates. The Montana and Autobahn real life experience of unposted limits having no apparent effect on safety can not be ignored.

After the repeal of the NMSL, Montana went to NO SPEED LIMITS outside of urban areas ON ALL ROADWAYS. Highway fatality and incapacitating injury rates remained within normal deviations. More interestingly to the discussion of speed limits, the "basic speed law" was ruled unconstitutional and the public knew they had no enforceable speed limits whatsoever. Fatalities were down during this period in 1998-99. The fatalities in 1999 were the lowest yet for the first half of the year, during the second half it has gone up.

Montana FARS Report

DATA FROM NHTSA FARS - (Fatal Accident Reporting System)
  Rural Interstate Rural Primary Total of Both % State Fatal Total Statewide
1994 41 51 92 50.5% 182
1995 33 48 81 34.5% 186
1996 39 54 83 46.4% 179
1997 51 56 107 48.0% 223
1998 30 54 84 40.3% 208
5 yr. average 39 53 89 43.9% 196
(Fall 95 - mid 99 no daytime speed limits)

Even though there was a dramatic drop from 1997 to 1998 with the lowest number of fatal accidents reported in modern times on Montana’s interstates, the 1995 number shows this is within normal deviation. Therefore, there is only one conclusion that can be drawn from Montana’s real life example, there is no apparent correlation between the number of fatalities, enforcement and posted limits on rural roadways.

2/01/00 Final Report: Montana – No Speed Limit Safety Paradox

The Montana experience solidifies the long held engineering axiom taken directly from the Washington State DOT website:

“that people don't automatically drive faster when the speed limit is raised. These are common misconceptions, along with the mistaken belief that speed limit signs will decrease the accident rate and increase safety, and highways with posted speed limits are safer than unposted highways”.

Author: Chad Dornsife
The Hwysafety Group
Box 141
Zephyr Cove, NV 89448