The National Cooperative Highway Research Program (NCHRP) Report 500 series is a collection of guides in which relevant information is assembled into single volumes, each pertaining to emphasis areas, specific types of crashes, or contributing factors. The guides correspond to the emphasis areas outlined in the American Association of State Highway and Transportation Officials (AASHTO) Strategic Highway Safety Plan.
The volumes of the NCHRP Report 500 series can be classified in the following two categories.
1. Safety Data.
2. Safety Issues and Countermeasures.
Volume 21, Safety Data and Analysis in Developing Emphasis Area Plans, is the single volume in the series related to safety data. It was developed to aid highway safety analysts in using the other implementation guides. Specifically, it can be used to identify data sources and analysis techniques that may be employed to support the decision-making process, including the allocation of safety funds.
The other volumes are related to specific safety emphasis areas, including those listed below. Each guide includes a brief introduction, a general description of the problem, the strategies/countermeasures to address the problem, and a model implementation process. The guides can be used in site diagnosis to better understand the underlying problem or safety issues related to a specific emphasis area. The guides can also be used to identify proven, tried, and experimental countermeasures to address specific safety issues identified in site diagnosis. The following factors are presented (when available) for each countermeasure/strategy for the user to consider during countermeasure selection.

• Target group or population.
• Expected effectiveness.
• Keys to success.
• Potential difficulties.
• Appropriate measures and data.
• Associated needs.
• Organizational, institutional, and policy issues.
• Issues affecting implementation time.
• Costs.
• Training and other personnel needs.
• Legislative Needs.

Volumes include:

• A Guide for Addressing Aggressive-Driving Collisions
• A Guide for Addressing Collisions Involving Unlicensed Drivers and Drivers with Suspended or Revoked Licenses
• A Guide for Addressing Collisions with Trees in Hazardous Locations
• A Guide for Addressing Head-On Collisions
• A Guide for Addressing Unsignalized Intersection Collisions
• A Guide for Addressing Run-Off-Road Collisions

. A Guide for Reducing Collisions on Horizontal Curves

• A Guide for Reducing Collisions Involving Utility Poles
• A Guide for Reducing Collisions Involving Older Drivers
• A Guide for Reducing Collisions Involving Pedestrians
• A Guide for Increasing Seat Belt Use
• A Guide for Reducing Collisions at Signalized Intersections
• A Guide for Reducing Collisions Involving Heavy Trucks
• A Guide for Reducing Crashes Involving Drowsy and Distracted Drivers
• A Guide for Enhancing Rural Emergency Medical Services
• A Guide for Reducing Alcohol-Related Collisions
• A Guide for Reducing Work Zone Collisions
• A Guide for Reducing Head-On Crashes on Freeways
• A Guide for Reducing Speeding-Related Crashes
• A Guide for Reducing Crashes Involving Motorcycles
• Safety Data and Analysis in Developing Emphasis Area Plans
• A Guide for Reducing Collisions Involving Young Drivers
• A Guide for Reducing Collisions Involving Bicycles

The following companion documents complement the series.

• NCHRP Report 501 – Integrated Safety Management Process (2003).
• Updated Transportation Planner’s Safety Desk Reference (February 2010).