Step 1. Compile Data and Resources

Overview

The first step in conducting safety analysis is compiling the available data. The type of safety analysis that can be conducted and its level of sophistication vary according to the quantity and quality of the data used. Valuable safety analysis can be conducted with very little data. The most common types of quantitative data used for safety analysis are crash data, traffic volumes, and roadway characteristics. Qualitative or anecdotal information from stakeholders also is commonly used in safety analysis.

In addition to data, documents and other readily available resources along with information and assistance from a variety of organizations and agencies can be referenced and enlisted as support for safety analysis.

This section provides information about:

• Anecdotal data;
• Quantitative data, including crash data, traffic volumes, and roadway characteristics;
• Data from existing resources and documents; and
• Organizations and agencies that can provide additional safety analysis support.

These types of data and resources are described in further detail below.

Data Examples

Anecdotal Data

Anecdotal data include phone calls from concerned citizens, community member survey results, news items, and local staff and police knowledge about a particular site or segment of roadway. These data provide a range of perspectives about potential safety issues, including speeding, limited sight distance, lack of signage, and roadway segments that frequently experience icy conditions. They are particularly useful in identifying sites with potential for safety improvements. Additional information, as well as ideas for potential solutions, can be gathered from these stakeholders as well.

Quantitative Data

Quantitative data include information from police reports, crash data, traffic volume data, and roadway characteristics.

Crash Data

Typical sources of crash data include local and state crash databases as well as local police crash reports and the National Highway Traffic Safety Administration (NHTSA) Fatal Analysis Recording System (FARS).

Quantitative versus Qualitative?

Quantitative: Deals with measurable data, such as speed, time of day, traffic volumes, numbers, and rates of crashes or fatalities.

Qualitative: Deals with things that can be observed but not easily measured, such as an individual’s perception of safety on a roadway, public attitudes towards DUI checkpoints, and various other descriptive information.

Local and State Crash Data. Local law enforcement agencies usually keep records of all crashes their officers have recorded. These crash reports are recorded on crash forms that are uniform across the state, but often differ between states. Despite differences in the forms, crash reports across all states generally contain data related to:

• Crash date, time, and location;
• Drivers and passengers (age, impairment, gender);
• Road condition at the time of the crash;
• Crash type;
• Crash severity;
• Weather conditions at the time of the crash; and
• Lighting conditions.

Most crash reports include a key that describes the meaning of the codes used in the form. Figure 2 is an example of a crash report form from Michigan.

In some states, the DOT collects and maintains crash data for all public roads. In others, the state police maintain a comparable data system. These databases enable summary crash data to be analyzed and reports to be generated. Many states also publish summary crash reports that can be useful to understand crash trends and provide contact information for data requests or support (for example, Oregon Department of Transportation’s annual crash report.

Figure 2. Example of Crash Report Form from Michigan

Source: Michigan Department of Transportation, UD-10 Traffic Crash Report Manual.

Crash data can be requested from the DOT or State Police. Staff in the traffic engineering or safety division of the DOT or Local Technical Assistance Program (LTAP)/Tribal Technical Assistance Program (TTAP) can provide guidance on requesting crash data. Typically, these staff study both engineering and behavioral-related (behavioral, including seat belts, driving under the influence of alcohol or drugs, texting/cell phone usage) crash issues and are therefore good resources for data analysis assistance and information about safety-related activities at the DOT. Be aware that due to processing and reporting issues crash data summaries are often published six to nine months after the end of a given calendar year.

NHTSA Fatal Analysis Recording System. All motor vehicle crashes with fatal injuries are recorded in the NHTSA Fatal Analysis Reporting System (FARS) database, as illustrated in Figure 3. FARS is an on-line database which can be queried to learn about fatal crashes in any jurisdiction.

Figure 3. Example from NHTSA FARS On-line Database

Source: NHTSA Fatality Analysis Reporting System (FARS) Encyclopedia.

Traffic Volume Data

Traffic volume data are routinely collected for traffic operations analyses, transportation planning activities, and analysis of traffic patterns. These data can be used in combination with crash data to calculate crash rates. Calculating crash rates is helpful because the number of crashes at a given location depends not only on roadway characteristics and driver behavior, but also on the volume of traffic or “exposure.” It is best to use crash rates as a tool to compare safety performance for sites with comparable traffic volume and roadway characteristics.

The types of traffic volume information that contribute to safety analysis include:

• Average Annual Daily Traffic (AADT). If AADT is not available, Average Daily Traffic (ADT) can be used to estimate AADT.
• Vehicle Miles Traveled (VMT). VMT is traffic volume on a segment of road multiplied by a segment length.
• Major and minor street AADT (or ADT) or total entering volume (TEV) for intersections. Intersection TEV is the sum of the traffic entering the intersection at all approaches.

Traffic volumes tend to vary with the type of roadway facility, the season, day of week, and the level of development. If an agency has a public works, engineering, planning, or traffic engineering department, it already may collect and record traffic volume data for local roads. State DOTs typically collect and record traffic volume data on state-owned roads (and in some cases non state-owned roads as well). The Handbook of Simplified Practice for Traffic Studies (see resources) provides information about collecting traffic volume data if none are available.

Roadway Characteristic Data

Many safety analysis tools use roadway characteristics data as an element of the analysis, including:

• Roadway Segment Characteristics. Characteristics of roadway segments include such items as roadway functional classification, number of lanes, length of medians or guardrail, and width and type of shoulder.
• Intersection Characteristics. Typical intersection characteristics include traffic control and signal phasing (if appropriate), number and type of lanes at each approach, sight distance, skew angle, and number of approaches.

Functional Classification

Streets and highways are grouped into classes, or systems, according to the character of traffic service that they are intended to provide.

Common functional classifications in a local environment are arterial, collector, and local roads. A road is planned and designed to be an arterial, collector, or local road based on the character of the traffic (i.e., local or long distance), the degree of land access provided and travel speeds.

Arterial – Provides the highest level of service at the greatest speed for the longest uninterrupted distance, with some degree of access control.

Collector – Provides a less highly developed level of service at a lower speed for shorter distances by collecting traffic from local roads and connecting them with arterials.

Local Roads – Consists of all roads not defined as arterials or collectors; primarily provides access to land with little or no through movement.

Agency public works, planning, or traffic engineering specialists may be familiar with or have access to roadway characteristics information. State DOTs have much of this information, at least for state-owned roads, because they are required to provide it for the National Highway Performance Monitoring System (HPMS) database. If roadway characteristics data cannot be obtained through these sources, they can be collected through field reviews or identified through review of on-line satellite images (Several sources can be used including Google Maps™ mapping service or Bing® Maps).

HPMS Information

Among many purposes, the state Highway Performance Monitoring System (HPMS) is used for understanding national highway system performance analysis, funding allocation analyses, and reporting to Congress. Roadway extent, use, condition, and performance data are described in the HPMS database which all states provide on-line.

Data in Existing Reports, Plans, and Documents

Often, crash data, traffic volume data, and roadway geometrics data are provided as part of the safety analyses conducted for various projects and reports. Statewide safety policy and planning documents also may contain information useful to local or Tribal practitioners studying safety. Example resources include:

• Strategic Highway Safety Plan (SHSP). Every state is required to have an SHSP. The SHSP provides a statewide strategic approach to reducing fatal and serious injury crashes on all public roads. It identifies the key safety issues in the state and provides approaches for addressing them. SHSPs typically contain information such as:
  • Crash types that are common across the state, and therefore potentially useful to the practitioner;
  • Treatments or actions to address these crash types for consideration statewide; or
  • Other state, local, and/or Tribal practitioners working on roadway safety issues.

  More information about SHSPs is available on the Strategic Highway Safety Plan page. This site also provides links to all state SHSPs.

State SHSPs present emphasis areas and strategies statewide and provide valuable information about the most important safety issues from the state’s perspective. Because of their broad, statewide scope however, they may not provide practitioners with localized data.

• Other Useful Reports or Information. State DOTs usually have processes and procedures in place for studying state roadways and identifying sites with potential for safety improvements. If a state-owned roadway traverses a local or Tribal jurisdiction, state planners and engineers are likely to have crash data, traffic volumes, and roadway characteristic information available. In some cases, a state or regional long-range transportation plan also may have a chapter devoted to roadway safety. This could also be a resource for information about crash trends, data sources, or staff available to support local analysis.

Most state DOTs have Tribal Government Liaison staff that are charged with working with sovereign Tribal governments on transportation issue. Tribal Liaison staff can be an easy access point for Tribal governments interfacing with the state DOTs or local agencies in their area.

Organizations or Agencies That May Be a Resource

Many organizations provide safety training, information, contacts, advocacy, and analysis support, including:

• LTAP/TTAP. Local Technical Assistance Programs (LTAP) and Tribal Technical Assistance Programs (TTAP) centers serve every state. Seven regional TTAP centers serve tribal governments by region across the country. The goal of these programs is to provide training, information, and resources to local and Tribal practitioners to address safety, security, congestion, capacity, and other issues on local and Tribal roads.

  Kentucky, Florida, Idaho, Iowa, New York, Pennsylvania, West Virginia, and the Northern Plains Tribal Assistance Program have Safety Circuit Riders. Safety Circuit Riders provide safety-specific training, resources and support for analyzing safety issues, studying sites, and identifying low-cost safety countermeasures. FHWA has published a best practices guide for safety circuit riders. The purpose of the guide is to help state DOTs and LTAP/TTAPs enhance existing Safety Circuit Rider programs. If a state does not have a Safety Circuit Rider, safety training, resources, and support are available through the LTAP/TTAP.

LTAP and TTAP Centers

Every state plus Puerto Rico has a LTAP center. There are also seven tribal centers (TTAP). LTAP and TTAP Centers are charged with helping local and tribal agencies with transportation problems through training and technical support.

• State DOT Local Assistance. State DOTs support some form of local assistance program or office. Staff in these offices are focused on helping local agencies solve transportation-related problems and also may administer Federal and state funds for local agencies. Staff in these offices are often excellent resources that understand project funding opportunities. They can also provide connections to key people within the DOT.
• State Highway Safety Office. Every state and territory has a Highway Safety Office (HSO). Representatives from the HSO are valuable resources and know a great deal about critical behavioral safety issues (behavioral safety issues include impaired driving, occupant protection, distracted driving, driving while drowsy) in the state. They can provide access to crash data as well as information about effective behavioral countermeasures and grant funding opportunities. State Highway Safety Offices submit annual Highway Safety Plans to NHTSA documenting strategies, actions, and performance-related to specific NHTSA performance measures.
• Regional Transportation Planning Organizations (RTPO)/Metropolitan Planning Organizations (MPO). Many RTPOs/MPOs have long-range transportation plans with information about existing and planned transportation networks and/or provide transportation safety-related support and technical assistance to local agencies. This support can include: compiling crash data, analyzing data, developing funding applications, or facilitating road safety audits.
• The Governor’s Highway Safety Association (GHSA) is a national advocacy and leadership organization that provides support to the Highway Safety Offices. The GHSA web site provides a wealth of information about behavioral safety issues, programs, funding sources, and a variety of other safety resources.
• FHWA State Division Offices. Each state has an FHWA Division Office. Staff from FHWA Division Offices provide support on a wide array of transportation planning and engineering topics, including roadway safety. Division Office staff can provide information about best practices appropriate to local and Tribal roads, solutions to specific safety issues, and connections to other available resources.

FHWA division offices generally have a Local Agency Engineer/Specialist that is specifically charged with interfacing with local and Tribal governments in their area.

• National Association of County Engineers. The National Association of County Engineers (NACE) is an association for practitioners responsible for county roads and bridges. The organization provides advocacy, networking opportunities, training support, and many other resources for county/parish engineers, transportation directors, highway superintendents, road supervisors, and highway administrators. The organization provides connections to other professionals working on transportation safety issues as well as on-line resources on a variety of transportation topics, including roadway safety.
• American Public Works Association. The American Public Works Association (APWA) is an education and networking resource for professionals, organizations and agencies responsible for “building, maintaining, and improving our communities.” (quote from APWA) APWA is a resource for staff seeking to learn more about managing transportation and road safety in their community.

Application

After compiling and reviewing the available safety data, its quality should be assessed. Answers to the following questions provide a good indication of data quality:

• How complete is the data. Does the data sufficiently cover the roadways and locations of interest?
• How current is the data. Does the data reflect current conditions at the site?
• How accurate is the data. Are there errors in the data that are readily apparent?
• How consistent or uniform is the data. If evaluating multiple sites, are the data more comprehensive for some sites than they are for others?

The type and quality of available data determine the type and quality of analysis that can be conducted. The more comprehensive and accurate the data, the more options there are for in-depth analysis. However, valuable results can be obtained even with limited data.

In some instances estimating data using best judgment is sufficient to advance the analysis. In such cases, documenting how the estimate was made and why objective data was not used, helps everyone involved understand the limitations associated with the estimation process and the results obtained from it.

Resources for Step 1: Compile Data

NCHRP 500 Safety Data and Analysis for Developing Emphasis Area Plans (Volume 21).

Source: National Cooperative Highway Research Program.

Section II of this document provides additional information about resources, opportunities and barriers associated with collecting and applying many of the data sources described above. Section III of this document also provides a process for identifying, evaluating, and identifying treatments for a specific safety concern. This publication can be found on the TRB web site.

Road Safety Information Analysis: A Manual for Local Rural Road Owners

Source: FHWA.

This manual was published in 2011 by the FHWA to provide information on crash data collection and analysis techniques specifically applicable to local practitioners with limited resources. It is intended to help improve safety on local rural roads by providing a background on data driven decisions. The manual is written in nontechnical language and designed to meet the needs of local road professionals, regardless of their educational background or experience.

Pages 4 to 12 of the manual summarizes the three common types of data needs for a safety project or program: crash data, roadway characteristics data, and exposure data.

The manual is FHWA Report Number: FHWA-SA-11-10.

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