developing standards and guidelines for establishing speed

Developing Standards and Guidelines for

Establishing Speed Limits on Unpaved Roads

By

Joshua R. Jones, E.I.T

Traffic Engineer

Wyoming T2 / LTAP

University of Wyoming

Laramie, WY 82071-3295

Joel Meena, P.E.

State Traffic Engineer

Wyoming Department of Transportation

5300 Bishop Blvd.

Cheyenne, WY 82003

Khaled Ksaibati, Ph.D., P.E.

Director Wyoming T2 / LTAP

Department of Civil and Architectural Engineering

University of Wyoming

P.O. Box 3295

Laramie, WY 82071-3295

Word Count: 5243 + 9 Tables/Figures * 250 Words = 7493 Words

Submitted for Presentation and Publication at the

91st Annual Meeting of the Transportation Research Board

Washington, D.C., 2011

TRB 2012 Annual Meeting Original paper submittal - not revised by author.

Jones, Meena, and Ksaibati 1

ABSTRACT

The lack of national standards for establishing speed limits on unpaved roads has put pressure on

local governments to make judgment calls on their road networks. Unpaved roads have unique

characteristics that differ from paved roads. They usually are very low volume and were not

necessarily designed by engineers. This study was conducted to determine the necessary

standards and guidelines for establishing speed limits on unpaved roads in Wyoming. The

process used national standards and other state practices to ensure a comprehensive methodology

was followed. A focus group comprised of traffic and safety engineers was formed to find an

efficient process for establishing speed limits on unpaved roads. The group focused on four

main aspects for establishing speed limits: data collection requirements, roadway safety, finding

the appropriate speed limit and the declaration of the speed limit. Once the standards and

guidelines were developed, five different groups were asked to provide feedback to ensure that

all stakeholders had an opportunity to review them. The findings of this study will help states

and counties follow a similar process or be able to adopt the standards and guidelines with minor

adjustments.



INTRODUCTION Establishing speed limits remains one of the more controversial tasks for the traffic engineering

profession. Engineers, public safety officials, and others involved in setting and enforcing speed

limits may disagree on the appropriate balance between safety and road-user convenience while

considering conditions of topography, weather, road surface, adjacent activities, and traffic.

Motorists, other road users, and roadway neighbors have their own perspectives on this balance

and may or may not abide by the professionals’ judgments. If the regulation of speed is to be

effective, the posted limit must be generally consistent with speeds that drivers feel are safe and

proper. Enforcement is widely recognized to be crucial to the success of speed limits as a means

of making roads safer. If law enforcement officers and the courts are confident that speed limits

have been developed on a reasonable basis, their enforcement of the limits will be more

effective. Generally, speed limits should be set at levels that are self-enforcing so that law

enforcement officials can concentrate their efforts on the worst offenders.

As of 2008, over 32% of the 4,058,000 miles of roads in the United States had unpaved

surfaces (1). Currently, there are no national standards or guidelines for setting speed limits on

unpaved roads. This has put pressure on local governments and counties to make judgment calls

on the correct speed limit. A lot of states use the same criteria for setting speed limits on

unpaved roads as on paved roads. This can create inconsistencies since unpaved roads have

many different characteristics including: very low traffic volumes, inadequate signing, varying

road conditions, narrow shoulders, varying road width, and many roadside hazards. In addition,

unpaved roads frequently evolved from trails or farm access lanes and were not designed by

engineers.

In Wyoming a new law came into effect in 2011 that reduced the statutory speed limit on

unpaved roads from 65 mph to 55 mph. Title 31, Chapter 5 – Article 3 of the Wyoming Statutes

establishes the speed regulations for all public roadways in Wyoming. The limits specified in

this subsection established a maximum lawful speed on an unpaved roadway at 55 mph. Any

speed limit, other than a statutory speed limit that is posted on a Wyoming unpaved road, must

be based on an engineering study. That study should include an analysis of free-flow traffic

speeds and a general roadway safety evaluation.

To help counties implement the new law, the Wyoming Department of Transportation

(WYDOT) and the Wyoming Technology Transfer Center (WYT²/LTAP) developed standards

and guidelines for establishing speed limits on unpaved roads. The standards and guidelines were

developed following a similar process that national agencies have used for paved roads. This

entailed a focus group that developed a decision process for establishing different speed limits.

Five different groups were contacted to get the necessary feedback from those who would be

directly impacted by the new standards and guidelines. These included WYDOT, local

governments at the transportation and safety congress, Wyoming County Commissioners

Association (WCCA), Wyoming Associations of County Engineers and Road Superintendents

(WACERS), and the general public.



The main objective of this paper is to outline the standards and guidelines which were

developed. The standards establish proper study procedures for completing the engineering

investigation in accordance with the statutes, provide guidance in setting appropriate speed limits

based on the study data, and specify the documentation and notification procedures needed when

establishing new speed limits on unpaved roads. These standards and procedures summarize the

minimum requirements to establish speed limits on unpaved roads. A professional engineer can

consider additional information when establishing speed limits. The guidelines described in this

paper can be implemented by other agencies managing unpaved roads.

NATIONAL STANDARDS AND GUIDELINES The Manual on Uniform Traffic Control Devices (MUTCD) states that “when a speed limit is

posted, it should be within 5 mph of the 85th

percentile speed of free-flowing traffic”. However,

the manual indicates other factors may influence the appropriate speed limit, including: roadway

characteristics such as shoulder condition, grade alignment, and sight distance; pace speed;

roadside development and environment; parking practices and pedestrian activity; and reported

crash experience for at least a 12-month period (2). Even though the MUTCD indicates that

these other factors can influence the speed limit decision, it does not quantify the impact of those

factors on the final speed limit decision.

The National Cooperative Highway Research Program has developed a web based

application called US LIMITS2 which recommends a speed limit on a specific road based on

information from the user. The application was developed in part to quantify the other roadway

characteristics besides speed data. US LIMITS2 calculates two speed limits; the first one

depends solely on roadway characteristics and the second one is calculated by considering crash

data.

Figure 1a shows the decision tree developed by US LIMITS2 for setting speed limits on

roadways in undeveloped areas. This was highlighted because unpaved roads are more related to

roadways in undeveloped areas than any of the other US LIMITS2 categories. The decision tree

starts with user input to help calibrate the model. It then asks the user if crash data is available

and if it is, the model calculates two speed limits. Speed limit one is based solely on the

roadway characteristics. For road sections in undeveloped areas, the roadside hazard rating is the

only road characteristic that is analyzed. The rating looks at the width of clear zone, side slopes,

and recoverability of run off the road situations. The ratings rank from 1 being the safest to 7

having the most risk associated with it. Figure 1b shows how the speed limit one is chosen based

on the rating number. The second speed limit is found by comparing crash data on similar roads

and if the road section under consideration has a higher than expected crash rate, then the second

speed limit is usually set lower than the 85th

percentile speed. The final speed limit is then found

by taking the lower of either values.



Figure 1a: Decision Process for setting speed limits in Undeveloped Areas (3).

Figure 1b: Speed Limit one Calculation on a Roadway Section in Undeveloped Areas (3).



Some of the shortcomings of the US LIMITS2 system for setting speed limits on unpaved

roads include the following:

There is no unpaved road option.

General process may not apply to Very Low Volume Roads (ADT < 400).

Roadside hazard rating may not apply to unpaved roads.

Higher variance between the 85th

and 50th

percentile speeds on unpaved roads is not

considered.

SPEED LIMIT PRACTICES IN OTHER STATES Michigan recently passed a law limiting speed limits on unpaved roads based on the number of

access points per half mile, as shown in Table 1. This law will stay in effect until Michigan State

Police finish their final report on guidelines for setting speed limits on gravel roads.

Table 1: Michigan Speed Limit Law on Gravel Roads (4).

Design Speed

Access Points

per 0.5 miles

25 60

35 45 - 59

45 30 - 44

55 < 30

In a study conducted by the Michigan DOT, The following recommendations were made

with regard to establishing speed limits:

Posting speed limits within 5 mph of the 85th percentile speed has a beneficial effect,

although small, on reducing total crashes but has a major beneficial effect on providing

improved driver compliance.

Posting speed limits more than 5 mph below the 85th percentile speed does not reduce

crashes and has an adverse effect on driver compliance.

Speed zoning should not be used as the only corrective measure at high crash locations in

lieu of other safety improvements (5).

An extensive gravel road study was done by Kansas State University in 2009. That study

focused on developing a system for determining the speed limit for a particular road section.

They found that the speeds being traveled on gravel roads had less to do with the actual speed

limit and were affected more by roadway geometrics, roadway characteristics, and drivers’

perceptions of safety (6). The study also found that some state DOTs, such as Oregon and

Minnesota, feel that because the conditions of gravel roads are always changing, it is not logical

to place a speed zone on such roads.



CalTrans doesn’t provide guidelines for setting speed limits on unpaved roads but does

offer a general process for setting speed limits on their roads. When a speed limit is to be posted

in California, it should be established at the nearest 5 mph increment of the 85th

percentile speed

of free flowing traffic. The posted speed may be reduced by 5 mph from the nearest 5 mph

increment of the 85th

percentile speed. If the 5 mph reduction is applied, the conditions and

justification for the reduced speed limit need to be documented in writing and be approved by a

registered civil or traffic engineer (7).

Texas DOT sets their speed limits based on the 85th

percentile and doesn’t allow the

practitioner to lower it. The procedure states that “Arbitrarily setting lower speed limits at point

locations due to a perceived shorter than desirable stopping sight distance is neither effective nor

good engineering practice (8).”

For low volume roads, the Vermont DOT uses several time runs to estimate the speed

instead of gathering a sample of 100 vehicles because it might require too much time to obtain

the sample. They require three forms to be completed for every speed study, including those on

unpaved roads, to be able to verify in court that it was done to standards. This helps give

enforcement agencies the confidence to issue speeding tickets knowing that the speed limit can

be verified. They also state that a spot hazard such as a sharp curve or intersection shouldn’t be

used to lower the speed limit. An established speed limit is a speed that will allow the driver to

react to a variety of situations but does not guarantee that the speed can be maintained

throughout the zone (9).

WYDOT currently has standards and procedures for setting speed limits on paved roads.

Their policy follows the MUTCD fairly closely but sets the lower bound of the pace speed as the

lowest acceptable speed limit. The pace speed is the 10 mph increment that encompasses the

highest proportion of observed speeds. When there is a wide range that a recommended speed

limit can be set to, the speed limit decision relies mostly on the engineer’s judgment. This can

create inconsistencies of how speed limits are set across the state (10).

METHODOLOGY The WYT²/LTAP and WYDOT followed a systematic process to develop the standards and

guidelines for establishing speed limits on unpaved roads. It was important to get feedback from

various organizations to insure successful implementation. This was critical since unpaved roads

are usually the responsibility of local governments. The following is the process that was used:

Conducted analysis on the WYT²/LTAP gravel roads traffic data.

Met with WYDOT district traffic engineers.

Developed draft standards.

Obtained approval from WYDOT’s chief engineer.

Obtained counties’ feedback at the WYT²/LTAP Safety Congress.

Obtained county engineers’ and road supervisors’ feedback at the WACERS meeting.

Presented the standards and procedures to the Wyoming County Commissioners

Association.



Incorporated input from the general public.

Implemented the standards and guidelines on July 1, 2011.

FOCUS GROUP The guidelines and standards were initially developed by conducting a focus group meeting at

the statewide traffic engineers meeting in Wyoming. The meeting had traffic and safety

engineers from multiple agencies as shown below:

State Traffic Engineer

District Traffic Engineers

FHWA Safety Engineer

State Highway Safety Engineer

WYT²/LTAP Engineers

Unbiased Survey

The meeting began by asking the group to fill out an unbiased survey. This was done to get the

individual members of the group to independently form opinions on setting speed limits on

unpaved roads before the meeting started. Table 2 shows the questions that were asked, the

percentage of participants’ choices, and any comments that were included. The group selected

the minimum value for the speed limit, access points, number of crashes and surface conditions

as critical variables when setting speed limits. A frequent comment was that many of the

variables are reflected in the 85th

percentile and don’t need to be considered separately as factors.

WYT²/LTAP Gravel Road Study The next step was a presentation of the Wyoming unpaved road speed data that was collected by

the WYT²/LTAP. Information on 82 Wyoming unpaved roads was collected to gain a better

understanding of traffic volumes and speeds. Table 3 shows that the average 50th

percentile

speed recorded was 31 mph while the average 85th

percentile speed was 40 mph. This shows

that, on average, there is a 9 mph gap between the two percentiles and showed that the 50th

percentile may be too low for the lower bound of the speed limit.

To understand the challenges of data collection requirements for unpaved roads, Figure 3

was presented to review the distribution of unpaved roads by ADT. It shows that the majority of

unpaved roads in Wyoming have less than 100 vehicles per day.



Table 2: Unbiased Survey Results. Question Choice Comments

Are there any circumstances which would

justify recommending a speed limit higher

that the 85th percentile?

67% - Yes,

33% - No

When improper limits have been set and not enforced,

it should be higher than the 85th percentile.

When setting speed limits to the 85th

percentile, should it be the rounded down or

up 85th percentile?

75% - Both should

be used, 25% -

rounded up

Depends on roadway characteristics.

Check the boxes of all the characteristics that

would warrant a speed limit lower than the

85th percentile:

N/A Adverse horizontal curves, poor gravel condition, high

number of crashes, roadside hazards, high number of

access points were chosen

If the recommended speed limit is lower than

the 85th percentile speed, check the values

that can be used:

67% - Yes,

33% - No

Lower bound of pace speed (55%), Minus 5 from the

85th percentile, Minus 10 from the 85th percentile.

Should the recommended speed limit have a

minimum value that can be used?

67% - Yes,

33% - No

Allowing or documenting this will most always get

posted. This may lead to artificially posted speed limits.

Should a ball bank test be performed on all

adverse horizontal curves for unsigned roads

before recommending a speed limit?

56% - Yes,

22% - No,

11% Maybe

Advisory on curves that are lower than the speed limit,

Consider chevrons and delineation instead.

Should the Average Daily Traffic (ADT) be

considered for recommending speed limits?

44% - Yes,

33% - No,

22% - Maybe

Effect of ADT is observed in the 85th tile, As long as

there is a valid sample size.

Should Average Daily Truck Traffic (ADTT)

be considered for recommending speed

limits?

56% - No,

22% - Yes,

22% - Maybe

Included in the 85%tile, Higher ADTT roads should

generally have lower limits.

Should the segment length be considered for

recommending speed limits?

44% - Yes,

44% - No,

12% - Maybe

Attempt should be made to reduce short speed zones

Should roadside clearance be considered for


44% - Yes,

44% - No,

12% - Maybe

Influence is seen in the 85%tile, If roadside clearance is

less than 5 feet than lower the speed limit.

Should the roadway classification (ie, rural

major collector, rural minor collector, and

rural local road) be considered for


44% - Yes,

44% - No,

12% - Maybe

Major roads should keep high speeds, collectors should

generally have higher speeds than local roads.

Should the type of adjacent land-use (i.e.,

residential, commercial, mining, agriculture

and industrial) influence the speed limit

decision?

44% - Yes,

66% - No

Influence is seen in the 85%tile, adjacent land-uses

with high truck traffic should have a speed limit less

than the 85th percentile

Should the surface condition of the road be

considered when recommending speed

limits?

78% - Yes,

22% - No

Influence is seen in the 85%tile, this will take care of

itself when collecting data, speed limit should be set for

ideal conditions.

Should the number of access points

considered for recommending speed limits?

67% - Yes,

33% - No

20 access points should warrant a reduced speed limit,

influence is seen in the 85th percentile.

Should the number of crashes on a road be

used when setting speed limits?

78% - Yes,

22% - No

Minus 10 mph form the 85th percentile, no lower than

30 mph

Table 3: Wyoming Unpaved Road Speed Data - 82 Observations.

50th

percentile

speed

85th

percentile

Speed

Average 31 40

85th

Percentile 41 52

Standard Deviation

Deviation

9.1 11.1



Figure 2: Distribution of Test Sections by ADT – 82 Observations

After the presentation of Wyoming unpaved road data, nine case studies were presented

where each study had different characteristics associated with it. The group individually

evaluated the first 2 while the next 7 were evaluated collectively. A “round table” discussion

followed where members discussed the pros and cons of each major decision. Table 4 shows the

speed data that was used for the case studies. All of the speed data was taken from actual roads

in Wyoming. On average only 44% of the vehicles recorded were in the pace speed. This

observation confirms that there is a higher variability in speeds on unpaved roads than on paved

roads.

05

10152025303540

Nu

mb

er

of

Ro

ads

Average Daily Traffic (vehicles/day)



Table 4: Speed Data for Case Studies.

Case Study/

Scenario

85th %

speed

50th %

speed

Lower Bound

of Pace (mph)

Upper Bound of

Pace (mph)

Percentage in

Pace speed

1 57.8 46.7 42.8 52.2 38.5%

2 38.3 29.6 25.8 35.7 42%

3 45 28.6 33.4 43.3 45.9%

4 45.8 35.6 24.9 34.8 36%

5 48.1 40.3 34.1 44 53.3%

6 40.9 30.7 26.7 36.6 36%

7 29.3 22 16.3 26.2 59.5%

8 47 39 35.5 45.4 48%

9 60.6 48.9 45 54.9 37.1%

Averages 45.9 35.7 31.6 41.5 44%

OUTCOMES OF THE FOCUS GROUP MEETING

The discussions at the focus group meeting were instrumental in developing the first draft of the

standards and guidelines. The group focused on four main aspects: the determination of an

appropriate speed limit, data collection, roadway safety, and declaration of speed limit. For each

major decision, a procedure was proposed and voted on by the group. A major concern of the

group was the data collection requirements for speed data. Unpaved roads are generally very

low volume roads which make some of the data collection techniques unfeasible.

Data Collection A big difference for setting speed limits on unpaved surfaces compared to paved surfaces is the

data collection. Most unpaved roads have very low volumes which presents challenges to the

traditional spot speed study. Also, weekends can bring larger volumes and less familiar drivers

onto the roads. This affects the speeds that are recorded and more importantly the safety of the

road. The focus group approved data collection procedures which incorporated many of the

aspects that effect unpaved roads.

Procedure 1 - For the engineering studies, vehicle speeds and traffic volumes should be

determined using automated traffic counters. For most low volume unpaved roads, seven

consecutive days of traffic counts are required. For unpaved roads with more than 200 vehicles

per day, 2 days of traffic counts may be adequate. The automated traffic count values that are

required are: 85th

percentile, 50th

percentile, upper bound of the pace speed, the Average Daily

Traffic (ADT) and the Average Daily Truck Traffic (ADTT).

A special form was developed to assist with the collection and analysis of the traffic

count data and the safety aspects of the road as shown in Table 5. The form includes five parts:

general information, automated traffic count values, roadway characteristics, historical crash

data, and range of speed limit values. In the form, the clear boxes correspond to the input that

trained technicians or engineers are required to provide. The gray shaded boxes correspond to



the calculations and information that the registered engineer is required to provide. When

collecting speed study data, the general information should be completed before proceeding to

the next steps. The required automated traffic count values can be obtained from the output file

that the automated traffic counters produce. As shown in Figure 3, the output file summarizes

the different speed and traffic volumes that the automated traffic counters produce.

Table 5: Unpaved Roads Speed Limit Data Collection Form



Figure 3: Automated Traffic Counter Output (11)

Roadway characteristics are collected during a field inspection of the road. The roadway

characteristics that were determined to be critical to the speed limit decision are:

Roadway Length

Number of Access Points

Roadway Width

Adjacent Land-Use

Type of Terrain

Roadway length was chosen so that speed zones in very short segments could not be set

using the standards and guidelines. Access points is an important characteristic because unpaved

roads have unplanned access points on the road that can create risk. On some unpaved roads, the

roadway width is limited which can make vehicles drive on the shoulder to accommodate two-

way traffic.

Adjacent Land-Use was chosen to associate the roadway with a demographic of drivers.

The choices for the adjacent land use are shown below and were obtained from AASHTO’s

Guidelines on Geometric Design for Very Low Volume Roads (12). The descriptions of each



adjacent land use highlight the type of vehicles and drivers that can be expected to traverse the

road.

Rural major access roads serve a dual function of providing access to abutting

properties as well as providing through or connecting service between other local road or

higher type facilities.

Rural minor access roads serve almost exclusively to provide access to adjacent

property. The length of minor access roads is typically short. Because their sole function

is to provide access, such roads are used predominantly by familiar drivers.

Industrial or commercial access roads serve developments that may generate a

significant proportion of truck or other heavy vehicle traffic. These roads are classified

separately from minor access roads, which they otherwise resemble, because of the

consideration for trucks and other heavy vehicles.

Recreation and scenic roads serve specialized land uses, including parks, tourist

attractions, and recreation facilities, such as campsites or boat-launch ramps. Their users

are often unfamiliar drivers and serve recreational vehicles including motor homes,

campers, and passenger vehicles pulling boats and other trailers.

Rural resource recovery roads are local roads serving logging or mining operations.

Resource recovery roads are distinctly different from the other functional subclasses of

very low-volume local roads in that they are used primarily by vehicles involved with the

resource recovery activities and the driving population consists primarily or exclusively

of professional drivers with large vehicles.

Rural agriculture roads are used primarily to provide access to fields and farming

operations. Vehicle types that use such roads include combines, tractors, trucks that haul

agricultural products, and other large and slow-moving vehicles with unique operating

characteristics.

Type of terrain refers to the general character of the road. This characteristic helps look

at sight distance and the alignment of the road in general terms so it can encompass the entire

road. This allows the technicians or engineers to speed up the data collection process and not

have to measure all of the sight distance and alignment issues. There are three different types of

terrain that can be chosen:

Level – Highway sight distances, as governed by both horizontal and vertical restrictions,

are generally long or can be made to be so without construction difficulty or major

expense.

Rolling – Natural slopes consistently rise above and fall below the road or street grade,

and occasional steep slopes offer some restriction to normal horizontal and vertical

roadway alignment.

Mountainous – Longitudinal and transverse changes in the elevation of the ground with

respect to the road or street are abrupt, and benching and side hill excavation are

frequently needed to obtain acceptable horizontal and vertical alignment. (12)



Roadway Safety The focus group decided that a general road safety evaluation should be considered when

determining speed limits. Such an evaluation should include the following:

If there are a high number of crashes on the roadway under investigation, then a detailed

crash analysis should be performed to find the causes of the crashes. Once the causes are

determined, then additional steps should be taken to provide safety enhancements for

high crash locations. Reducing the speed limit by itself will not automatically reduce

crashes.

The road should be driven at a reasonable and safe speed to determine if any curves

require vehicles to slow down. Further safety enhancements such as signage, delineation,

shoulder widening, and guardrails should be considered at adverse curves.

When horizontal curves are signed, they should include either chevrons, delineators or

curve warning signs. Speed advisory signs are not required on unpaved roads.

Speed limits should not be reduced due to the presence of isolated fixed objects such as

utility poles, trees, rocks or narrow cattle guards. Consideration should be given to using

object markers, removing the hazard or widening the road at those locations.

The speed limit should never be lowered to reduce the number of signs needed on a road.

The general roadway safety section was meant to provide recommendations rather than

outlining required procedures. An important decision was to not require that all curves have a

“ball bank test” performed. It was thought that it would take too much time and effort to analyze

every curve with a ball bank test. On unpaved roads, gravel buildup and constant grade changes

lead to a speed that is not consistent around curves. Also trucks can travel faster around curves

than smaller vehicles making the ball bank test car specific and difficult to advise a speed for all

vehicles. Because of this, it was recommended to sign the adverse curves with delineators or

chevrons instead of advisory speeds.

It is recommended that 10 years of crash data be included in the evaluation. The

following three types of crashes are evaluated: number of fatalities, number of injuries, and the

number of Property Damage Only (PDO). The Equivalent Property Damage Only (EPDO) can

then be calculated by using Equation 1.

(Equation 1)

Once the EPDO is calculated, the EPDO per mile is determined by dividing the EPDO by

the roadway length. If there are a high number of crashes, then a detailed crash analysis should

be performed to determine if speed is a factor in the crashes.



Determination of Appropriate Speed Limit

After collecting all the required data, a registered engineer can recommend a speed limit for

unpaved roads to the county commission. When recommending the speed limit, the focus group

felt that the registered engineer should consider the following procedures:

Procedure 2 - The preferred speed limit is the 85th

percentile speed rounded to the nearest

5 mph.

Procedure 3 - A professional engineer can consider other roadway characteristics to

justify a lower speed limit. But the lowest acceptable speed limit may only be up to 10

mph less than the 85th

percentile speed.

Procedure 4 - The recommended speed limit on unpaved roads shall never be higher than

the statutory speed limit of 55 mph

Declaration of Speed Limit Form Posted speed limits (other than statutory speed limits) on unpaved roads that have been

established by an engineering investigation must be documented by a Declaration of Speed

Limit. A declaration of speed limit form is shown in Figure 4.

When declaring a speed limit, the declaration of speed limit form must be signed and

sealed by a professional engineer. The form, with appropriate background information, is then

presented to the county commission where a resolution number approving the proposed speed

limit is issued. The resolution number will then be added to the declaration of speed limit form.

The form is then returned to appropriate county officials so that the necessary signing changes

can be made. Enforcement of the new speed limit cannot occur until the appropriate signs giving

notice thereof are in place. It is also recommended that copies of the resolution be sent to the

local law enforcement agency(ies) for help with enforcement.



Figure 4: Declaration of Speed Limit Form

FEEDBACK ON THE STANDARDS AND GUIDELINES Five different groups provided feedback on the developed standards and guidelines after the

focus group meeting. They are:

WYDOT Chief Engineer.

Local governments attending the Transportation and Safety Congress.

Wyoming Associations of County Engineers and Road Superintendents (WACERS).

Wyoming County Commissioners Association (WCCA).

General Public. The Chief Engineer of WYDOT wanted to make sure that the counties and

commissioners had input since they were going to be the ones in charge of implementing the

standards and guidelines. He also wanted the WCCA to have input on what the correct process

was for declaring a speed limit. During the presentation at the WYT²/LTAP Safety Congress, it

was advised that all speed limits set before the standards and guidelines were finalized could be



considered valid and wouldn’t need a new study as long as they were done in accordance with

WYDOT’s procedures. The WACERS committee recommended that the lower bound of the

recommended speed limit be changed from minus 5 mph to minus 10 mph from the rounded 85th

percentile. It was brought up to a vote and all 11 of the committee members voted for the

change. The WCCA recommended that a resolution number be assigned to every new speed

limit. That way if it is brought up in court they can find the resolution number and find all the

supporting information that is needed. It also simplified the process of declaring a speed limit.

SPEED LIMIT WORKSHOPS As part of the implementation of the standards and guidelines, the WYT²/LTAP will provide

training workshops to train county technicians and engineers on how to set speed limits on

unpaved roads. WYDOT worked out an agreement so that the WYT²/LTAP can establish speed

limits on local roads, if the counties collect the necessary data. A workshop training manual was

developed to explain all the steps and procedures in more detail. The following process is a

general outline on how the Center will assist and train counties and municipalities with setting

speed limits on unpaved roads:

1. Automated Traffic Counters

a. The Center will provide training on the equipment and the software.

b. The Center will provide training on the location and set up of the equipment.

2. Roadway Characteristics

a. The Center will provide training on how to collect the roadway characteristics that

are required for the study.

3. Safety Evaluation

a. The Center will provide training on the safety evaluation that should take place

during the speed study. This includes identifying low cost measures for

improving the safety of unpaved roads.

4. Declaration of Speed Limit Form

a. The Center will provide training on the steps to be taken when declaring a speed

limit. This includes the required documentation and signatures.

SUMMARY AND CONCLUSIONS The lack of national standards for establishing speed limits on unpaved roads proved to be a big

challenge for this study. However it also provided an opportunity for Wyoming to assist other

agencies that are pursuing the same type standards. The standards developed in this study can be

adopted with minor modifications by any agency managing unpaved roads.

The standards and guidelines for establishing speed limits on unpaved roads were

developed through an extensive process that allowed all stake holders a chance to provide timely

feedback. The standards and guidelines provide Wyoming counties with a step by step process

and the documentation needed for establishing speed limits on unpaved roads.



According to the developed standards and procedures the following steps should be

followed when establishing speed limits on unpaved roads:

A registered engineer or a trained technician can collect the necessary data. For the

engineering studies, vehicle speeds and traffic volumes should be determined using

automated traffic counters. For most low volume unpaved roads, seven consecutive days

of traffic counts are required. For unpaved roads with more than 200 vehicles per day, 2

days of traffic counts may be adequate. The automated traffic count values that are

required are: 85th

percentile, 50th

percentile, upper bound of the pace speed, the Average

Daily Traffic (ADT) and the Average Daily Truck Traffic (ADTT).

The road should be driven at a reasonable and safe speed to determine if any curves

require vehicles to slow down. Further safety enhancements such as signage, delineation,

shoulder widening, and guardrails should be considered at adverse curves.

Speed limits should not be reduced due to the presence of isolated fixed objects such as

utility poles, trees, rocks or narrow cattle guards. Consideration should be given to using

object markers, removing the hazard or widening of the road at those locations.

The preferred speed limit is the 85th

percentile speed rounded to the nearest 5 mph.

A professional engineer can consider other roadway characteristics to justify a lower

speed limit. But the lowest acceptable speed limit may only be up to 10 mph less than

the 85th

percentile speed.

The recommended speed limit on unpaved roads shall never be higher than the statutory

speed limit of 55 mph.

The declaration of speed limit form needs to be sealed by a registered engineer then

approved by the county commission with a resolution number.

The training workshops will provide comprehensive knowledge to the county engineers

and technicians and let them know exactly what is expected of them. It also provides an

opportunity for practitioners to understand why the procedures are needed. The safety aspect of

the workshop will provide an opportunity to illustrate safety tools that can be used on all county

roadways. A major benefit is that the WYT²/LTAP will analyze the data free of charge if the

counties collect the necessary data.

This project will help create more uniform speed limits on unpaved roads and give the

public confidence that they were set appropriately. The enforcement of the speed limits will be

more efficient because police officers will feel that they were set appropriately and will only be

ticketing the worst offenders. It will also give the enforcement and judicial system confidence that

speed infractions will be upheld in the court of law.

ACKNOWLEDGMENTS The authors of this paper would like to thank WYDOT, Wyoming Association of County

Engineers and Road Superintendents, and the Wyoming County Commissioners Association for



their contributions in helping develop the standards and guidelines for establishing speed limits

on unpaved roads.



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United States by Type of Surface: Current as of January 1, 2008.

http://www.bts.gov/publications/national_transportation_statistics/html/table_01_04.html

(accessed July 2011)

2. Federal Highways Administration. Manual on Uniform Traffic Control Devices. 2009.

3. NCHRP, Transportation Research Board. Expert System for Recommending Speed Limits

in Speed Zones. Project No. 6-67, November 2006.

4. Dissanayake, S. Criteria for Setting Speed Limits on Gravel Roads. Journal of

Transportation Engineering, ASCE, 2011.

5. National Motorists Association. Comparison of Speed Zoning Procedures and Their

Effectiveness. Report No. 89-1204, September 1992. http://www.motorists.org/speed-

limits/comparison-zoning (accessed June 2011)

6. Dissanayake, S. and L. Liu. Speed Limit Related Issues on Gravel Roads. Report No. K-

Tran: KSU-06-5, Kansas Department of Transportation, 2009.

7. California Department of Transportation. Traffic Operations Policy Directive. Policy No.

09-04, June, 2009.

8. Texas Department of Transportation. Procedures for Establishing Speed Zones. Manual

Notice No. 2011-1. February 2011.

9. Vermont Local Roads Program. Setting Speed Limits, A guide for Vermont Towns. June,

1995.

10. Wyoming Department of Transportation. WYDOT traffic studies manual. 2009.

11. JAMAR Technologies, Inc. TraxPro Program. 2010.

12. AASHTO, Guidelines for Geometric Design of Very Low-Volume Local Roads.

American Association of State Highway and Transportation Officials, Washington, D.C.,

2001.


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