banner of Methodology for Determining Motorcycle Operator Crash Risk and Alcohol Impairment

1. Background

Drinking Rider Problem

In 2004, 4,008 motorcyclists were killed and an about 76,000 were injured in traffic crashes (NHTSA Traffic Safety Facts, 2004). Motorcyclist fatalities have been steadily increasing since 1997 when 2,116 fatalities were recorded.

It is apparent that alcohol use continues to be a significant problem in motorcycle crashes. In fatal crashes in 2004, a higher percentage of motorcycle operators had BAC levels of .08 g/dL or more, higher than any other type of motor vehicle driver. The percentages for vehicle operators involved in fatal crashes were 27 percent for motorcycles, 22 percent for passenger cars, 21 percent for light trucks, and 1 percent for large trucks.

Also, in 2004, 28 percent of all fatally injured motorcycle operators had BAC levels of .08 g/dL or higher. An additional 6 percent had lower alcohol levels (.01 – .07), and 41 percent of 1,672 motorcycle operators who died in single-vehicle crashes had BAC levels of .08 g/dL or higher.

Other important findings concerning alcohol use in fatal motorcycle crashes from Shankar (2003) include the following:

  • Alcohol involvement in fatal crashes among motorcycle operators has shown an improvement from 49 percent in 1992 to 37 percent in 2001. However, still over one-third of operators were alcohol-positive in fatal crashes in 2001, with a majority of them intoxicated (BAC≥.08).
  • Males were operating the motorcycle in 97 percent of fatal motorcycle crashes.
  • Riders in the 40- to 49-year-old age group had the highest percentage of alcohol involvement (46%).
  • Alcohol was involved in 49 percent of single-vehicle fatal motorcycle crashes and 25 percent of multiple-vehicle fatal motorcycle crashes.
  • Alcohol was involved in 54 percent of nighttime fatal crashes and 19 percent of daytime fatal crashes.
  • Three-fourths of operators involved in fatal crashes between midnight and 3 a.m. were alcohol-positive.
  • Motorcycle operators not wearing helmets or who were improperly licensed or speeding at the time of a fatal crash were more likely to be alcohol-positive than other operators.

Project Objectives

In 2000, the National Agenda for Motorcycle Safety (NAMS) cited alcohol as a “prominent factor in serious motorcycle crashes” (NAMS, 2000). It states that we need a better understanding of the following:

  • Why alcohol continues to play a role in motorcycle crashes more frequently than in those of other vehicles;
  • Alcohol use and substance abuse patterns of motorcyclists; and
  • The role of alcohol and substance abuse in motorcycle crashes.

This report summarizes the results of a NHTSA-sponsored project to assess alternative methodo­logical approaches for determining the effects of varying blood alcohol levels on alcohol-impairment among motorcyclists as well as motorcyclists’ likelihood of crash involvement. Some of the methodologies examined would provide information on alcohol’s impairing effects on motorcycle operation. Others would provide a measure of relative risk of crash involvement through the comparison of crash data with population-at-risk data.

This project was performed by a team comprised of staff from the Pacific Institute for Research and Evaluation (PIRE) of Calverton, Maryland, and the Head Protection Research Laboratory (HPRL) of Paramount, California. The basic approach involved the project team developing a literature review document (see Vol. II) and providing it as a background document to a panel of national experts. The panel was invited to a workshop to discuss, compare, contrast, and rate various methods of data collection.  Subsequently, project staff, using panel member comments and priorities, created a system for prioritizing the various research methodologies discussed in this project.

One way to determine the relative risk of being involved in a crash when a motorcyclist has been drinking would be to collect and analyze both motorcycle exposure and crash data. The crash data becomes the numerator and the exposure data is the denomi­nator for use in statistical comparisons and analysis. Currently, there is no national resource for both crash and exposure data for motorcyclists. Of course, crash data is reasonably well documented. Generally the more serious the crash outcome, the better documented the crash is. The Fatality Analysis Reporting System (FARS) is NHTSA’s nationwide resource for fatal crash data. There is no comparable data set for motorcycle exposure data.

In addition to crash risk it is possible to obtain a fuller understanding of the effects of alcohol on motorcycle operation by examining performance based changes (decrements) and decision errors associated with drinking alcohol.  Studies involving use of riding simulators and motorcycles operated on closed course have been used to assess rider impairment.

The methodologies under consideration for this project should ultimately permit addressing the questions regarding the likelihood of being involved in a crash at various BAC levels—questions such as “Are motorcycle riders more vulnerable at lower BAC levels compared to drinking auto­mobile drivers?” The methodologies considered may also allow more effective targeting of counter­measures to those who drink and ride, by answering questions such as “Are younger riders at a greater risk of crash involvement after drinking compared to older riders at similar BAC levels?”

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