U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
|Table of Contents
There are a number of information sources that can be accessed to get a picture of the roadway departure issues on the rural roadway network. These can be formal information sources or informal sources, including:
Examining the crash history will help practitioners identify locations with an existing roadway departure problem, and it will also provide information to identify locations that are susceptible to future roadway departure crashes. In addition to the location, the data can also provide information regarding crash causation. This will provide insights into identifying potentially effective countermeasures.
For the systematic treatment of roadway departure crashes based on proven low cost countermeasures, the available crash data is used to determine where specific crash types are predominant.
Emphasis on data-driven decisions is indicative of reliability and efficiency. The more reliable the data, the more likely the decisions regarding safety improvements will be effective. However, detailed, reliable crash data are not available in all areas. Under this circumstance the practitioner should use the best available information and engineering judgment to make the best decisions.
As a guideline, it is generally accepted that at least 3 years of historical data be used for crash history analysis, though additional years of data can provide more information. Due to the randomness of crashes in a given year, a multi-year average of safety data will smooth outlier years of relatively high or low roadway departure crash occurrences. If only severe crashes are analyzed (those that resulted in a fatality and/or serious injury), more years of data may be necessary for effective evaluation. In using data more than 5 years old, however, the practitioner should consider possible changes in traffic patterns and infrastructure when conducting the analysis.
Each state has a central repository for storing crash data. This is generally the most comprehensive data for roadway safety analysis, particularly if all public roads are included in the database. Several states share this information with the local road agencies. Alternatively, many states that do not currently share the raw crash data often provide comprehensive data analysis to local agencies upon request.
If the data are available, the local road practitioner can use these data to identify locations with multiple roadway departure crashes, conduct an analysis that can produce predominant crash types, and identify associated roadway features that may have contributed. The local agency can work with the State to compare its crashes to those occurring in similar areas around the state.
This information can be used for both spot location treatments and systematic deployments, depending on the details of the collected data. For example, if a high number of crashes are occurring at a particular curve or along a segment of roadway, a spot treatment at that location may be appropriate. However, systematic treatment of multiple locations experiencing specific crash types or location with the potential for those crash types may be necessary.
Action: Obtain at least 3 years of data to identify local roads that have a history of roadway departure crashes. Identify predominant roadway departure crash sub-types and other common characteristics.
Begin a spreadsheet of crashes, law enforcement reports, and citizen notifications by starting with crash history data (see Table 1). This can serve as a database to help an agency identify common crash characteristics and identify the appropriate countermeasures.
Both State and local law enforcement officials can be an important source of roadway departure crash data. Law enforcement crash reports can be valuable in identifying the location and contributing circumstances to roadway departure crashes. For these crash types, the following variables (at a minimum) should be extracted and compiled from the crash reports:
The local practitioner using multiple sources of law enforcement crash reports should be aware that they may differ by jurisdiction; however, the basic information is always included and should provide sufficient data to identify crashes on local roads.
Similar to the crash database, the information in the crash reports can be used to assist in the identification of potential treatments and deployment approach.
Action: Develop a relationship with law enforcement officials responsible for enforcement and crash investigation on their roads. This could foster cooperation in sharing crash reports and safety information and collaboration on problem roadway segments.
Many local jurisdictions do not have formal crash databases, and some State databases do not include local road crash data. Additionally, some local entities may not have a local police force, and in some cases State forces may not share their crash reporting with these local entities. In this case, the local road practitioner can still conduct field assessments to help determine the safety of the roadway network.
Regardless of data availability and quality or the implementation approach, a field assessment should be conducted at selected locations. Assessing locations in the field provides additional information to the local practitioner that will factor into issue identification and countermeasure selection.
An assessment can be as informal as driving or walking the road network looking for evidence of roadway departure crashes. An informal field assessment can be performed by an in-house multidisciplinary team with a traffic safety expert and law enforcement personnel. The team can visit several sites and document evidence of crashes or deficiencies on the roadway or roadside. Examples include damaged trees or fences, skid marks, ruts on the shoulder, car parts on the shoulder, and/or pavement drop-offs. This information can be used to develop recommendations for improvement.
Field reviews can also be more formalized in the form of a Road Safety Audit (RSA). An RSA is a formal safety performance examination of an existing or future road by an independent, multidisciplinary team. The team examines and reports on potential road safety issues and identifies opportunities for safety improvements for all road users.
As with other sources of information, evidence discovered in a field assessment can help support spot location treatments and/or systematic deployments, depending on the information found. For example, if evidence is found of multiple roadway departure crashes on a single curve (due to multiple ruts on the roadside, fence repairs, or vehicle parts found on the roadside from more than one vehicle), a spot treatment may be appropriate to address safety at the curve. If similar types of crashes are occurring on several curves on the roadway network, then systematic deployment of appropriate countermeasure(s) can a viable solution.
Law enforcement officers and local crews who maintain the roads can serve as valuable resources to identify problem areas. Since they travel extensively on the local roads, they can continuously monitor the roads for actual or potential problems (e.g., poor delineation, fixed objects near the roadway, missing signs, signs of vehicles leaving the road).
Law enforcement officers patrol the local jurisdiction at night and on weekends when most public agency employees are not in the field. Their observations of driver behavior and roadway elements at these times can provide valuable insight to the local road agency. Additionally, law enforcement officers are sometimes aware of problem areas based on citations written, even if crashes related to the violations have not yet occurred.
Road maintenance crews often keep logs of their work, including sign replacements and edge drop-off repairs. These logs can provide supplemental information about crashes that may have not been reported to law enforcement.
Very similar to field assessments, information obtained from road maintenance crews and law enforcement officers while they are completing their normal duties can help support all three methods of implementation – spot location treatments, systematic deployments, and the comprehensive approach. Often, offenses such as speeding and impaired driving lend themselves to education and enforcement solutions to address these behaviors and supplement infrastructure countermeasures.
Action: Add information received from law enforcement and road maintenance crew observations to the spreadsheet (see Table 1).
Add information received from law enforcement citations to the spreadsheet.
Develop a system for maintenance crews to report and record observed roadway departure safety issues and a mechanism to address them.
Occasionally, when unsafe situations are observed, local citizens may notify the local government by email, letter, telephone call, or at a public meeting. While this is anecdotal information, these sources can serve as indicators that a safety issue may exist; the notifications potentially warrant further review and analysis to determine the extent of the issues.
Information identifying safety issues on local roads may also come from community or regional newspapers and newsletters or correspondence from local homeowner and neighborhood associations. This information can help pinpoint which segments are candidates for review, and it can support the local agency's relationships with the community that will benefit the safety program.
Action: Review and summarize the information, identifying segments or corridors with multiple notifications and recording the locations, dates, and nature of the problem that is cited.
Add information received from public notifications to the Table 1 spreadsheet.
It is also valuable to obtain information about the roadway infrastructure. The following roadway data are often used to assist practitioners in safety analyses on roadway segments:
This information can be combined with crash data to help local practitioners identify appropriate locations and treatments to improve safety. For example, if a local rural segment is experiencing a high number of horizontal curve-related crashes, analysis of the inventory of roadway elements could reveal that the roadway does not have sufficient signing installed in advance of many of those curves.
The raw number of crashes can sometimes provide misleading information about the most appropriate locations for treatment. Introducing exposure data helps to create a more effective comparison of locations. Exposure data provide a common metric to the crash data so roadway segments and intersections can be compared more appropriately.
The most common type of exposure data used on roadway segments is traffic volume. A count of the number of vehicles can provide information to the practitioner for comparison. For example, if two roadway segments have the same number of crashes but different traffic volumes, the segment with fewer vehicles (i.e., less exposure) will have a higher crash rate, meaning that vehicles were more likely to have experienced a crash along that roadway segment.
In situations where traffic volume is not available, segment length can serve as an effective exposure element for comparison.
|Source of Information
|Type of Information
|Nature of Crash
|Time of Day
|Date of Action
|Rt 123, 2 miles North of Fox Mill Road
|Route 123 West / 1/2 mile South of intersection with Fox Mill Road to intersection
|Drivers losing control at curve
|Miller's Curve on Route 430, 3 miles South of city limits
|Driver ran off road at curve
|Route 657; 1/2 mile South of Glade Drive
|Driver hit tree on shoulder; single vehicle
|Route 657; 1/4 mile South of Glade Drive
|Driver ran off road; single vehicle
|Clifton Road; South of Veirs Mill Road
|Driver ran off road on curve; exceeding posted speed
|Oakwood Road near Jones Elementary
|Route 657; 1/4 mile South of Glade Drive
|Oakwood Road just North of post office
|Trees covering warning signs
|Middlebrook Pike; 1 mile North of Running Cedar Road
|Numerous tire tracks on curve approach
|Advanced Curve Warning Signs Added
|Table of Contents