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

Executive Summary


In 2004, 4,008 motorcyclists were killed and an additional 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, motorcycle operators had higher blood alcohol concentration (BAC) levels ( .08 grams per deciliter [g/dL] or higher) as compared to other types of motor-vehicle operators. 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.

In 2004, there were 1,264 motorcycle operators killed who had been drinking (BAC .01+), of whom 1,025 (81%) were intoxicated (BAC .08+).

Drinking and driving has been researched extensively, and the association between drivers' BAC and crash risk is well-understood.  On the other hand, there is insufficient research to understand the effects of BAC on motorcycle operation, which is very different from automobile operation due to issues of balance, coordination, and vulnerability. Though there are BAC data available for some crash-involved riders, there are essentially no data available on the incidence of alcohol involvement in the on-road motorcycle-riding population.

The National Highway Traffic Safety Administration sponsored a project to investigate alternative methodological approaches for determining: (1) the relative risk of alcohol impaired motorcycle riders being involved in a crash and, (2) rider impairment at different BAC levels. This project was conducted in two steps: first by reviewing the literature, and second, by inviting a panel of national experts in alcohol and field data collection to a workshop to discuss, compare, contrast, and rate various methods of data collection.  The results of this project are reported in two volumes:

  • Volume I: Synthesis Report on Alternative Approaches with Priorities for Research – This report summarizes the project findings, including a detailed account of information discussed at an expert panel workshop convened for this project.  Among the topics discussed at the workshop were the advantages, disadvantages, scientific validity, and costs related to each alternative methodology.  In addition, each methodology was prioritized as to its future research potential.
  • Volume II: Literature Review Report – This report discusses past research on impaired motorcycle operation, past research methodologies used to understand alcohol’s effects on human performance, and methodologies used to measure exposure in populations-at-risk.  This report was provided to panel participants in support of the expert panel meeting.  Two appendices are included.  The first contains detailed descriptions of documents referenced in the report.  The second contains detailed descriptions of documents reviewed for the report, but not referenced.


A literature search was performed that focused on: (1) past research on impaired motorcycle operation; (2) past research methodologies used to understand alcohol’s effects on human performance, including laboratory simulation, closed-course operation, self-report surveys, crash investigation, and analysis of archival crash data; and (3) methodologies used to measure exposure in populations-at-risk, including roadside surveys. The literature review revealed a dearth of relevant research on impaired motorcycle operation. The most significant problem identified was the lack of scientifically valid information on BAC levels among on-road non-crash-involved motorcycle riders (i.e., the motorcycling population at risk). A total of 143 reports and Web sites were reviewed for this project;  61 of these are cited in the Reference sections of Volumes I and II, and described in detail in Appendix A.  Appendix B provides detailed descriptions of documents reviewed but not cited in either Volume I or Volume II of this report.   In addition, an in-house study of fatal motorcycle crashes was also conducted and discussed in this report.

An expert panel was assembled. Panel members were specialists in motorcycle safety, alcohol, and survey research, as well as law enforcement and other related fields. For each methodology under consideration, advantages, disadvantages, cost, and other issues were discussed.  At the end of discussion, panelists provided their personal opinions as to which methodologies should be considered the highest priority for future research, based on feasibility and validity of the research methodologies.

Methodologies Assessed

The following methodologies were considered as being potentially capable of contributing to a better understanding of crash risk and alcohol impairment among motorcycle operators. Some of the methodologies listed provide data from crashes. Some provide comparison data from the population at risk. Some would provide both.  Most would require collecting new data, though the last method listed could be done with existing data.

Studies Providing Data on the Impairing Effects of Alcohol

Simulation Study—Using a laboratory-based motorcycle simulator with alcohol-dosed subjects, impairment can be determined by comparing performance of each rider at various positive BAC levels.   Performance at different BAC levels are compared to the same rider’s performance when sober (.00 BAC) on different measures, such as rider balance, steering control and other rider tasks.

Closed-Course Study—Alcohol-dosed subjects would ride a motorcycle at low speeds on a closed (off-road) course outdoors. Performance of riders at various BAC levels would be measured and compared to their performance at the .00 g/dL BAC level.

Field Studies Providing Both Crash and Comparison Data

Contemporary Case Control—Data associated with crashes (including BACs of riders) is recorded and compared to similar data from non-crash-involved riders at or near the same location as the crash. Factors such as time of day and day of week would be matched carefully between crash and comparison cases.

Cohort Study—A sample of riders would be selected and alcohol use (e.g., BAC while riding) would be recorded over time, under naturalistic riding conditions along with data on any crashes that occur. Data would be collected using an instrumented motorcycle (to obtain BAC data, etc.) and other methods, including surveys and diaries.

Emergency Department—Similar to Contemporary Case Control study except that the interview with the crash-involved rider and BAC testing take place at a hospital.

Survey Study—Traditional survey techniques (e.g., phone, mail, or in-person surveys) would be used to collect self-reported data from riders concerning alcohol use and crash histories. Survey respondents would answer questions about past drinking and riding incidents which may or may not have resulted in a crash. Height, weight, gender, and number of drinks consumed would be used to estimate BAC of riders during these drinking and riding incidents.  Crash risk would be determined from these self-reports. 

Studies Providing Crash Case Data

Fatal Crash Records—BAC data from motorcycle rider cases in the Fatality Analysis Reporting System (FARS) would be obtained and compared to BAC data from motorcycle population-at-risk (exposure) data from a different source.

Injury Crash Records—BAC data on motorcycle riders from hospital records of motorcycle non-fatal injury crashes would be compared to population-at-risk data from a different source.

Studies Providing Comparison Data

Geo-General Comparison Data—Population-at-risk BAC data would come from general roadside surveys of motorcyclists, not from specific sites of previous crashes.  Crash data would come from a different source (e.g., FARS).

Geo-Specific Comparison Data—Population-at-risk BAC data would be collected from visits to specific sites of previous motorcycle crashes found in archival data, such as FARS, which serves as the crash data source.

Fuel Station Survey—This would be similar to the roadside collection of BAC and other data except that the survey takes place when riders stop to refuel. Data is then compared to data from another source (e.g., FARS).

Study Using Existing Data for Crash and Comparison Cases

Induced Exposure—Using archival data (e.g., FARS), the BACs of crash-involved riders deemed not to be at fault would be used for the population-at-risk and compared to BAC data for at-fault riders.


Based on input from the expert panel, each methodology was assigned to one of the three following cost categories: Low Cost = <$250K, Medium Cost = $250K-$500K, and High Cost = >$500K. Within each of these cost categories, methodologies were assigned to one of three levels of scientific validity (high, medium, and low), that is, the expected scientific validity of findings from the methodologies, given the barriers to collection of complete and accurate data. The assessment of scientific validity was determined by the contractor’s project team, based on input from the expert panel, results of the literature review, and past experience of the project team. With some exceptions, the methodologies rated highest for scientific validity were considered to be highest priority within their cost categories. Assigning priorities within cost categories will make it possible to select different promising methodologies depending on the funds available for future research. In one case, a methodology that would be highly valid scientifically (the cohort study) was rated a low priority because it would likely be so costly and time consuming as to be prohibitive to conduct. In another case, a methodology of relatively low scientific validity (induced exposure) was given a high priority by the project team because it would likely be very inexpensive to conduct.  The authors point out that the cost categories are fairly broad, and that relative priorities could change as more exact cost information for each methodology becomes known.

Highest Priority Methodologies

The highest priority methodologies determined by the project team are as follows: 

  • Lowest Cost Category—Simulation, Induced Exposure
  • Medium Cost Category—None
  • Highest Cost Category—Contemporary Case Control

Medium Priority Methodologies

  • Lowest Cost Category—Closed-Course Study
  • Medium Cost Category— Fuel Station Survey paired with Fatal Crash Records, Fuel Station Survey paired with Injury Crash Records
  • Highest Cost Category—Emergency Department, Geo-Specific paired with Fatal Crash Records

Lowest Priority Methodologies

  • Lowest Cost Category—None
  • Medium Cost Category—SurveyStudy
  • Highest Cost Category—Geo-General paired with Fatal Crash Records, Cohort Study


Compared to drinking and driving, relatively little is known about the effects of alcohol on motorcycle operation.  There are many methodologies that could be used to better understand these effects, each with its own set of advantages, disadvantages, and issues to be considered.  None of the methodologies considered as part of this project were completely ruled out by the project team, although three methodologies were deemed highest priority:  the Simulation and Induced Exposure studies, from the low-cost category, and the Contemporary Case Control study from the highest cost category.