Glossary
Actigraphy: The monitoring of time spent asleep using an actigraph, a device often worn on the wrist that assumes lack of movement indicates the wearer is asleep.
American Transportation Research Institute (ATRI): A nonprofit research organization that is a member of the American Trucking Associations.
Biomathematical models: Mathematical models that predict the impacts on performance of various work/rest schedules, including the effects of extended wake durations or rotating shifts. Very simple versions of such models are used to analyze two systems: sleep/wake homeostasis and the circadian biological clock.
Body mass index (BMI): A measure of a person’s degree of obesity, which is obtained by dividing the person’s weight (in kilograms) by the square of his or her height (in meters).
Carrier: A truck or bus carrier is a business that owns trucks or buses, respectively, and, unlike independent owner-operators, employs drivers to meet its driving needs.
Case-control study, cohort study, case-crossover study: A case-control study compares subjects who have a response or outcome of interest with those who do not in order to determine whether the two populations
differ in the frequency of potential causal factors. This analysis assumes that the two groups of subjects are otherwise similar with respect to any confounding factors, and this similarity can be achieved through pairwise matching and other techniques. In a cohort study, subjects are followed prospectively to determine which risk factors are and are not associated with the development of some condition or outcome of interest over time. A case-crossover study is similar to a matched-pair case-control design, except that the matched pair in this case is the same subject at two different points in time.
Circadian rhythm: Based on an internal biological clock that regulates when one has periods of sleepiness and wakefulness during the day. For many people, the period of greatest sleepiness comes between 2:00 and 4:00 AM, with a lesser period occurring between 2:00 and 4:00 PM.
Commercial driver’s license (CDL): Required to drive a commercial motor vehicle. To obtain a CDL, one must pass both a skills test and a knowledge test.
Commercial Driver’s License Information System (CDLIS): A nationwide computer system of commercial driver’s licenses that allows state driver’s licensing agencies to determine whether a commercial driver has any out-of-state convictions or other similar information. The central site is maintained by the American Association of Motor Vehicle Administrators.
Commercial motor vehicle (CMV): Either a single vehicle with a gross vehicle weight rating of 26,001 or more pounds; a combination of vehicles with a gross vehicle weight rating of 26,001 or more pounds if a vehicle being towed is more than 10,000 pounds; a vehicle that carries 16 or more passengers, including the driver; or a vehicle that transports hazardous materials.
Commercial Vehicle Safety Alliance (CVSA): An international nonprofit organization comprising motor carrier safety officials and industry representatives from the United States, Canada, and Mexico, with the mission of promoting commercial motor vehicle safety and security. As part of its mission, CVSA establishes out-of-service standards for commercial vehicles operating in North America, and its inspections can place a vehicle out of service if violations are discovered during the inspection process.
Confounding factor: A factor that may be causally associated with some outcome of interest and is not of primary interest in a study.
Disclosure avoidance, disclosure protection (sometimes called statistical disclosure avoidance, statistical disclosure protection, disclosure control, or other similar terms): A collection of techniques used to protect confidential individual-level information while at the same time retaining as much of the information as possible in a database that does not provide individually identifiable information.
Drowsiness or fatigue: Drowsiness refers to feeling sleepy or tired or being unable to keep one’s eyes open. Fatigue is a more general and subjective term that refers to increasing performance variability and instability in behavioral alertness and vigilance due to continued time on task without breaks.
Electronic-on-board recorder (EOBR): A device that is used primarily to log when a vehicle was in operation for some recent period of time—essentially the same as electronic logging devices (ELDs), and in contrast to paper logs.
Employee health and wellness programs: Encompass various methods for educating, incentivizing, and providing feedback to employees about their diet, exercise, and sleep habits to improve their health and wellness over time.
Exposure data: The amount of time or distance driven. Vehicle-miles traveled (VMT) is a common measure of exposure.
Fatality Analysis Reporting System (FARS): A database containing information on all motor vehicles involved in fatal traffic crashes in the United States, maintained by the National Highway Traffic Safety Administration (NHTSA).
Fatigue risk management plan (FRMP) and fatigue risk management system (FRMS): A fatigue risk management plan establishes policies on managing and mitigating fatigue during operations. It typically includes a requirement for employee (e.g., drivers, fleet managers, dispatchers) fatigue awareness training, as well as processes for reporting instances of fatigued driving. A fatigue risk management system manages operator fatigue at a more granular level, and includes a continuous feedback loop that provides a means for continuous measurement and monitoring of an individual worker’s schedules.
Federal Highway Administration (FHWA): An agency within the U.S. Department of Transportation that, through financial and technical assis-
tance to state and local governments, supports the design, construction, and maintenance of the U.S. highway system so that it is safe and technologically up to date.
Federal Motor Carrier Safety Administration (FMCSA): An agency within the U.S. Department of Transportation with the mission of preventing commercial motor vehicle-related fatalities and injuries. Its activities include enforcing safety regulations, targeting high-risk carriers and commercial motor vehicle drivers, improving safety information systems and commercial motor vehicle technologies, strengthening commercial motor vehicle equipment and operating standards, and increasing safety awareness.
General Estimates System (GES): A database based on a hierarchical stratified sample of police-reported crashes involving at least one motor vehicle engaged in travel on a roadway and resulting in property damage, injury, or death, maintained by the National Highway Traffic Safety Administration (NHTSA).
Hours-of-service (HOS) regulations: Set by the Federal Motor Carrier Safety Administration (FMCSA), they specify the maximum number of hours in a day and in a work week that commercial motor vehicle drivers can drive and work, along with other rules on breaks and restart provisions.
Hypopnea/apnea: Measures of a lack of oxygen during sleep. The number of times a person is awakened during sleep per hour is called the apnea/hypopnea index. It includes breathing cessations, or apneas, and partial obstructions, or hypopneas.
Instrumental variables: A statistical technique that controls for confounding and measurement error in observational studies and so promotes the potential for drawing causal inferences. In particular, in regression models, an explanatory variable X may be associated with the error term (which combines the effects of factors not included in the model), with the result being biased regression coefficients. An instrument Z is one that is causally related to X, that affects the outcome variable Y only through its impact on X, and that is independent of the error term, and therefore in replacing X, will provide unbiased estimates of the regression coefficients.
Large Truck Crash Causation Study (LTCCS): A collaborative research project between the Federal Motor Carrier Safety Administration (FMCSA) and the National Highway Traffic Safety Administration (NHTSA) to col-
lect detailed information on the possible causes of 963 large-truck crashes that took place between 2001 and 2003. The resulting database has supported a great deal of study of the causes of large-truck crashes.
Motor Carrier Management Information System (MCMIS): A census of all trucks and buses involved in a crash that involved a fatality, an injury to a person transported for immediate medical attention, or at least one vehicle towed because of disabling damage. It is maintained by the Federal Motor Carrier Safety Administration (FMCSA).
National Highway Traffic Safety Administration (NHTSA): Established to prevent highway crashes, in part by supporting research on their causes and how they can be prevented. Its focus is more on the safety of the vehicle and the driving environment than on the driver.
National Institute for Occupational Safety and Health (NIOSH): An agency within the Centers for Disease Control and Prevention that carries out research to reduce work-related illnesses and injuries.
National Registry of Certified Medical Examiners (NRCME): A list, established by the Federal Motor Carrier Safety Administration (FMCSA), of medical professionals who have completed training and successfully passed a test on FMCSA’s physical qualification standards for working as a commercial motor vehicle driver. These professionals can then be used to determine whether a commercial motor vehicle driver is physically fit to drive. A commercial motor vehicle driver whose medical certificate expires must be examined by a medical professional listed in the NRCME to retain driving privileges.
National Transportation Safety Board (NTSB): Charged with determining the probable cause of transportation accidents and promoting transportation safety, and with assisting victims of transportation accidents and their families.
Naturalistic driving study (NDS): A study that collects video and other data on the performance of a vehicle while the driver is carrying out his or her usual driving duties. The Strategic Highway Research Program (SHRP) 2 is a recently completed large naturalistic driving study of automobile drivers.
North American Fatigue Management Program (NAFMP): An online educational program designed to promote greater understanding of
effective ways to manage and mitigate fatigue in trucking and busing operations.
Observational study: A study in which researchers observe subjects and measure variables of interest without assigning treatments to the subjects, so that the treatment each subject receives is beyond the control of the researcher.
Obstructive sleep apnea (OSA): The most common type of sleep apnea, a sleep disorder in which breathing repeatedly stops and starts during sleep. In OSA, one’s throat muscles intermittently relax and block one’s airway.
Odds ratio: A measure of the association between a risk factor and an outcome. The odds ratio is the probability that an outcome will occur divided by the probability that it will not in the presence of a risk factor, divided by the same ratio when the risk factor is not present.
Owner-Operator Independent Drivers Association (OOIDA): A North American trade organization that represents the interests of truck drivers and works to affect state and federal legislation regarding the trucking industry.
PERCLOS (percentage of eye closure): A measure of the percentage of eyelid closure over a period of time—one of the most accepted measures of drowsiness.
Polysomnography: A sleep study that records the following body functions as subjects either sleep or try to sleep: air flow in and out of the lungs, the level of oxygen in the blood, body position, brain waves, breathing effort and rate, electrical activity of muscles, eye movement, and heart rate.
Positive airway pressure (PAP)/continuous positive airway pressure (CPAP) devices: Devices that are effective for treating obstructive sleep apnea. They work by blowing pressurized air through the airway to keep the throat open.
Propensity scores: A statistical technique that uses an estimate of the probability of treatment as a function of a set of potential confounding factors in various ways to balance a study’s treatment and control groups for the effect of those confounding factors.
Psychomotor vigilance test (PVT): A reaction-timed test that measures behavioral alertness and attention by measuring psychomotor speed, lapses of attention, and impulsivity induced by fatigue.
Restart provision: As part of the current hours-of-service regulations, drivers may “restart” their 7/8-consecutive-day duty period after 34 or more consecutive hours off duty.
Rubin’s causal model: A causal effect is defined as the nonzero difference between potential outcomes (one of which must be counterfactual) when different treatments are administered at a particular point in time under otherwise identical conditions.
Rumble strips: A road safety feature designed to alert fatigued or inattentive drivers that they are leaving their lane or the roadway by causing a vibration and an audible rumbling sound when a vehicle’s tires pass over them.
Safety-critical events (SCEs): Often identified by various kinematic motions of the vehicle, they are thought to be events that could have been crashes if the circumstances of the driving environment had been only slightly different.
Safety culture: A culture of shared beliefs, practices, and attitudes within an establishment that shapes behavior. It can include management and employee norms, beliefs, and attitudes; policies and procedures; supervisor priorities; responsibilities and accountability; and employee training and motivation.
Short-haul vs. long-haul drivers: Short-haul drivers often drive no farther than 150 miles from home and return home most evenings. Long-haul drivers often drive farther than 150 miles, and their trips often require them to sleep away from home.
Technologies for crash avoidance: Include electronic stability control (ESC), roll stability control (RST), lane departure warning (LDW), blind spot warning (BSW), forward collision warning (FCW), adaptive cruise control (ACC), and collision mitigation braking systems (CMBS).
Telematics: A set of technologies that use sensors to monitor the performance of a motor vehicle, including braking, steering, and speeding.
Truckload versus less-than-truckload services: Less-than-truckload services combine shipments from multiple shippers and transports to multiple destinations. Truckload services typically entail a load from a single shipper that is to be transported to a single destination.
Trucks Involved in Fatal Accidents (TIFA) and Buses Involved in Fatal Accidents (BIFA): Two databases that resulted from censuses of medium and heavy trucks and of buses, respectively, involved in fatal crashes. Both were based on the Fatality Analysis Reporting System (FARS), supplemented by data collected by University of Michigan Transportation Research Institute (UMTRI) researchers.
Vigilance: “The ability to maintain sustained attention within the road environment” (Thiffault and Bergeron, 2003). Alertness is roughly synonymous with vigilance.
