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                        Speed Management: A Manual for Local Rural Road Owners


            
            In This Section
        Local and Rural Road Safety Program
                Training, Tools, Guidance and Countermeasures for Locals Practitioners
                Crash Facts
                
                2. IDENTIFY SPEEDING ISSUES
The greater tendency to speed in rural areas may be due to the typically lower traffic volumes there. In some locations, the geometry of the roadway may selfregulate motor vehicle speeds. On the other hand, the geometric and roadside characteristics of a roadway may encourage higher speeds, such as on flat, open areas. Because speed enforcement activities may be sporadic in rural areas, speeding may go undetected or underreported until a severe crash occurs, at which time an immediate reaction may be to reduce the posted speed limit. Studies have shown that lowering the speed limit without justification does not effectively lead to reduced vehicle speeds. Therefore, a systematic process must be employed in addressing speeding.

The first step in such a process is to identify if there is a speeding issue and, if so, determine its magnitude and contributing factors. This entails data collection, an assessment of the posted speed limit, and a determination of whether speeds are excessive. It also involves the review of available crash and roadway data to isolate the factors contributing to the problem. If there is a documented speeding issue, then countermeasures are selected and coordinated with partner agencies and other stakeholders.

2.1 Data Sources

Road owners can become aware of locations with speeding issues through a number of sources:

Crash records.
	Road conditions.
	Citation history.
	Partner agencies.
	Citizen concerns.An analysis of crash records provides a solid foundation for identifying speeding problems. In some States, there is a specific data element on the crash report for the police to code the crash as speed-related. As a result, speed-related crashes in those States can be more-readily identified from the crash data. Typically, at least three years of crash data are necessary to be able to identify trends.

Some local agencies may maintain a crash records database. The agency that collects and maintains crash data varies by State and may include the State’s DOT, Department of Motor Vehicles, State Police or Highway Patrol, or Department of Public Safety. The appropriate agency can assist a local agency with obtaining crash data. A local practitioner can also contact the local law enforcement agency or the LTAP/TTAP representative to determine the availability of crash data. The Strategic Highway Safety Plans (SHSPs) in some States may include speeding as an emphasis area, so an SHSP may provide background information on the source of the data or identify opportunities to coordinate with other agencies.

The crash analysis can range from creating a simple "push pin" map (on which clusters of crashes attributed to speeding are located) to conducting a more detailed review of crash reports that can be used to identify other speed-related crash issues (e.g., crash type, time of day, weather conditions, and crash severity). For example, a high incidence of run-off-road crashes may be an indicator of speeding as a contributing factor.

In addition, exposure should be considered when analyzing crash data. Considering exposure allows for the more appropriate comparison of roadway segments or intersections. Two common types of exposure elements include crashes by roadway miles and crashes by traffic volume. More information on analyzing crash data is provided in *Roadway Safety Information Analysis: A Manual for Local Rural Road Owners.*

There may be evidence on the roadway that indicates there is a speeding problem. This evidence will not establish whether drivers were exceeding the speed limit or driving too fast for conditions but may provide information on locations where speed is a concern. This can be verified through agency staff actively observing conditions along the roadways that they routinely travel. Physical conditions that may indicate a speeding problem include the following examples:

**Skid marks** are the result of rapid braking. One set of skid marks is not likely to indicate a chronic problem. However, multiple sets of skid marks could indicate a condition where motorists are choosing an inappropriate speed and are braking suddenly to correct their speed.
	**Rutting** on the outside of curves can indicate that motorists are choosing speeds too fast for the curve design. The ruts indicate a loss of control through the curve.
	**Worn centerline markings** on the inside of curves can indicate that motorists are choosing speeds too fast for the curve design.
	**Sign knockdowns or guardrail/fencing strikes** may indicate speeds too fast for roadway conditions. Evidence of sign knockdowns or guardrail strikes may be coupled with rutting.Citations for speeding are another source of information about a speeding problem. Law enforcement often collects and maintains citation data that can be used to identify patterns in speeding. Linking these data to crash data provides a good understanding of the extent of the problem.

Concerns raised by a citizen or elected official are often based on personal observations and perceptions and should, therefore, be verified with field evidence. A concern expressed by an employee of a governing agency or law enforcement group is often based on evidence that can be found in the field or in the citation records. Regardless, the Speed Management Program should have a procedure for processing information brought forth by citizens and partner agencies. This information should be verified with crash data and citation records.

2.2 Assessing Speeding

Once an area of concern has been identified, and it has been determined that speeding is occurring, the next step is to determine any site-specific factors in speeding. As a starting point, the agency should address the following questions:

Has the posted speed limit been set in accordance with accepted procedures for the location?
	Do the accepted procedures consider the types if users, such as vulnerable users like pedestrian and cyclists, and slower vehicles, such as farm equipment? Are other environmental characteristics considered?
	Are unexpected conditions being encountered, such as a transition into a developed area or a change in the geometry of the roadway?
	Are motorists provided with sufficient information regarding an unexpected condition (e.g., a gateway treatment or signage noting a change)?
	Are there any engineering deficiencies in the roadway or roadside, such as inadequate pavement markings or signing, that may be contributing to the observed speeding? For example, in a rural village, speeds may be higher than expected if the travel lanes and parking spaces are not properly marked, creating extremely wide lanes.Although, a thorough review of police crash reports for an area of concern can provide insights, an agency should conduct a field review of the identified sites under free flow traffic conditions, which are usually observed outside of peak periods. Free flow traffic conditions are essential when studying a location to capture the natural tendencies of motorists unencumbered by traffic. Peak traffic conditions typically occur during the morning commute to work, lunchtime, the evening commute from work, and some special occasions (such as certain holidays). Field reviews can be either informal (e.g., using only an agency’s own personnel) or formal (e.g., a road safety audit using an independent multi-disciplinary team).*(5)*

Understanding the factors in speeding will help identify effective speed management strategies.

2.2.1 Assessing the Speed Limit

Speed limits are only meaningful if the majority of motorists comply voluntarily, and that occurs only if a speed limit is reasonable for the conditions and meets drivers’ expectations. There are two methods for establishing speed limits: the first involves applying the statutory speed limit, while the second involves establishing a speed limit through an engineering study.

Statutory speed limits are established by the authority of law in each State. Some State laws provide speed limits for all roads on the basis of functional class (i.e., arterial, collector, or local road) but are not limited to these speed limits if there is an overriding concern.*(6)* In many cases, these speed limits typically apply in the absence of a posted speed limit and usually do not preclude the establishment of a speed limit based on an engineering analysis of site-specific conditions.

On the other hand, some States may provide reduced *prima facie* speeds under certain conditions. For example, speed reductions may be warranted based on access point/driveway density (i.e., an indication of how many driveways are located in a specific section of roadway). Local rural practitioners should understand the laws that govern speed limits in their State. If the speed limit is not mandated by State law, then an evaluation of a speeding concern provides an excellent opportunity to review the appropriateness of the posted speed limit.

Research has shown that setting speed limits based on driver behavior and the adjoining land use can reduce the number of speeding citations, speed variance, and, most importantly, speeding-related crashes.*(7)* The establishment of a speed limit based on an engineering study allows for consideration of local conditions, such as geometry and crash history. FHWA provides an easy to use tool—USLIMITS, a Web-based expert advisor—for determining speed limits.*(8)* The following information is needed to conduct a typical speed limit determination using USLIMITS:

Land use type (e.g., high density, low density, hamlet, or rural).
	Frequency of roadside access (e.g., number of residential and commercial driveways, intersecting roads, etc.).
	Road function (e.g., traffic movement versus access to abutting properties).
	Facility characteristics (e.g., paved width, divided or undivided, lane width and number of lanes, sight restrictions, etc.).
	Current vehicle speed data (e.g., data from a speed study).
	Existing speed limits.
	Special conditions that may exist (e.g., adverse alignment, the presence of pedestrians and cyclists, roadside design, high crash rates, etc.).Other information on establishing speed limits can be found in *Methods and Practices for Setting Speed Limits: An Informational Report**.**(9)*

2.2.2 Determining if Speeds are Excessive

A speed study should be conducted in order to assess whether vehicle speeds are in excess of the posted speed limit and/or compatible with conditions. Appendix A (How to Conduct a Speed Study) provides guidance for conducting a speed study. Speed limits are often set by the 85th percentile speed, which is the point in the speed distribution at which 85 percent of vehicles travel at or below.

Use of the 85th percentile speed concept is based on the theory that the vast majority of drivers can be characterized by the following:

They are reasonable and prudent.
	They do not want to be involved in a crash.
	They desire to reach their destination in the shortest possible time.A speed at or below which 85 percent of people drive at any given location under good weather and visibility conditions may be considered as the maximum safe speed for that location.

The results of numerous and extensive "before-and-after" studies substantiates the general value of the 85th percentile criterion. Experience has also proved these findings valid and shows that the 85th percentile speed is the one characteristic of traffic speeds that most closely conforms to a speed limit that is considered safe and reasonable.

The data collected during the speed study is typically plotted on a graph as depicted in Figure 2. The graph plots the cumulative percentage for increases in speed. From this plot, the 85th percentile can be determined, which in this example is 33.2 mph. The light blue line depicts the actual speed measurements on the road in question and the dark blue line depicts the 85th percentile speed. More information on how to conduct a speed study is provided in Appendix A or can be found in the *Handbook of Simplified Practice for Traffic Studies.**(10)*

"Graph. A graphical depiction of how to determine the 85th percentile speed. The actual speed measurements on the road in question are plotted against the percentage of drivers. Zero drivers are driving at 5 MPH  at 33.2 MPH, 85 percent of drivers are driving at or below that speed. The chart peaks at 40 MPH, which is at the 100th percentile."

**Figure 2. Graphical Depiction of 85th Percentile Speed.**

2.2.3 Unpaved Roads

There are over 1.4 million miles of unpaved roads in the United States. In many rural areas of the country, local road agencies do not have any paved roads under their jurisdiction. Unpaved roads (e.g., limestone, natural aggregate, dirt, and sand) require special consideration when determining appropriate speed limits.

"Photo. A rural unpaved road. "

***Unpaved roads frequently do not have posted speed limits.***

Although usually low-volume facilities, unpaved roads typically lack adequate runoff areas, clear zones, and guardrails, making them more prone to injury and fatality-producing crashes. Hence, this type of road may require special consideration if a speed issue is identified.

A 2007 study conducted in Kansas supports the notion that gravel roads are fairly self-regulating with regard to speeds because of physical conditions, such as geometry, road width, and surface.*(11)* Speeding issues on gravel roads will be best addressed through the use of a combination of engineering, enforcement, and education countermeasures.
      
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                Book:Speed Management: A Manual for Local Rural Road Owners
              1. Introduction
                2. IDENTIFY SPEEDING ISSUES
                3. IDENTIFYING COUNTERMEASURES
                4. IMPLEMENTING COUNTERMEASURES
                5. SUMMARY
                References U.S. DEPARTMENT OF TRANSPORTATION

**Federal Highway Administration**

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