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Introduction to Highway Safety Analysis – Part 2

By Matt Hiland
June 30, 2009

This article is the second in a series that provides a high-level look at the typical data and processes for highway safety analysis.
Crash Reports

A crash report is a legal record of a traffic crash. Different states collect different data and use different forms to do so, but most of them collect at least some elements in each of the following categories:

  • Crash
  • Vehicle
  • Person
  • Environment and Factors

Crash Data

General data about the crash includes the date, time, location, and others. The date, time, and location of a crash are critical to further analysis of its causes and possible safety improvements. The crash location can be identified in several ways, including but not limited to:

  • Two intersecting roads
  • Distance and direction from two intersecting roads
  • Road and mile marker (linear measure along the road)
  • Road and GPS coordinate
  • Address
  • Visual placement on a map

Vehicle Data

Information collected about each vehicle involved includes but is not limited to:

  • Type (passenger car, SUV, motorcycle, truck, etc.)
  • Age
  • Insurance
  • Damage severity
  • Vehicle actions

Person Data

Some information is collected about all people involved in the crash, but more is collected for the drivers of each vehicle. Data collected includes but is not limited to:

  • Person type (driver, occupant, pedestrian, etc.)
  • Driver’s license number, status, and type
  • Name, address
  • Injury severity (extra information is collected if the crash is fatal)
  • Use of alcohol or drugs
  • Restraint system/helmet use

Environment and Factors

Additional information is collected about the road(s) on which the crash occurred, the conditions at the time and location of the crash, and other factors with either the vehicle or driver that may have contributed to the crash. These include but are not limited to:

  • Driver’s condition (sleepy, drunk, distracted, etc.)
  • Vehicle condition (faulty steering, brakes, etc.)
  • Road condition (wet, icy, potholes, etc.)
  • Light condition (dark, daylight, etc.)

Roadway Data

Data about the roads is usually maintained in a GIS. The roads are represented as a series of connected lines that make up a linear network. The ability to translate textual location descriptions (such as “100 feet north of the intersection of Highway 5 and Highway 36”) to spatial locations along the linear network is handled by a Linear Referencing System (LRS).
Different states collect and maintain different data about their roads. Key attributes for safety analysis include but are not limited to:

  • Traffic Volume
  • Road Class (Interstate, US Highway, State Highway, etc.)
  • Road Configuration (Two-way undivided, divided, median type and width, shoulder type and width, etc.)
  • Roadway Sections and Intersection
Linear sections of roads are typically analyzed differently from intersections of roads. Point features are often created from the road network to represent intersections. The intersections have similar attributes to road sections, but also have some additional ones such as:
  • Traffic Control (signal, stop sign, flashing light, etc.)
  • Turn Lanes
  • Intersection traffic volume

In Part 3, we’ll look at highway safety analysis processes.