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Developing Valid Estimates of Motorcycle Vehicle Miles Traveled

Valid estimates of motorcycle accident injury risk depend on accurate estimates of both numerators and denominators.  Numerators include values such as the number of fatalities or the number of injuries.  On the other hand, typical denominators include the number of registrations, riders licensed to operate a motorcycle or the number of miles traveled by motorcycles.  Because motorcycle use is seasonal in some parts of the United States and year-round in others, licenses and registrations do not provide a good estimate of accident risk associated with exposure in traffic.  At present, the only widely available estimate that includes motorcycle exposure is vehicle miles traveled (VMT), which is an estimate of the total number of miles traveled by all motorcycles in the United States, usually on a per-year basis.  Motorcycle VMT estimates have been compiled by the Federal Highway Administration, which simply aggregates motorcycle VMT estimates provided by each state.   There appears to be no uniformity of motorcycle VMT estimation method among the states, and no validation of the accuracy of various methods. 


One result of this variability and uncertainty is that estimates of motorcycle VMT appear to correlate poorly with other trends in motorcycling.  For example, VMT estimates showed little fluctuation from 1982 – 2002, even though in the mid-1990s motorcycle registrations and fatalities dropped to approximately two-thirds of their 1982 levels.  Motorcycle VMT estimates declined 10% between 1999-2002, even as motorcycle registrations increased by 20%, sales of new motorcycles soared by 63%, and motorcycle fatalities rose by 68%. 


Trustworthy estimates of motorcycle exposure in traffic are needed.  It is recommended that NHTSA or FHWA explore and test the validity and reliability of various methods of estimating motorcycle exposure in traffic, and develop guidelines for states so that they can produce more valid and reliable estimates of motorcycle usage. 


Objective:            Identify a reliable means for estimating accident risk for motorcyclists.  If VMT is to be used, develop guidelines for states that will result in more reliable estimates of motorcycle exposure in traffic.


Key Words:            VMT, Exposure, Motorcycle, Population at Risk, Accident


Urgency/Priority:          High




User Community:            Government and private motorcycle safety community, manufacturers, Insurance carriers.
Sponsoring Committee:ANF30, Motorcycles and Mopeds
Date Posted:08/04/2007
Date Modified:08/06/2007
Index Terms:Vehicle miles of travel, Motorcyclists, Motorcycle accidents, Motorcycle safety, Accident prone drivers, Accident risk forecasting, Injury severity, Crash injury research, Injuries,
Cosponsoring Committees: 
Data and Information Technology
Safety and Human Factors

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