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63 GLOSSARY Benchmarking--To compare company practices and out- sors. Subjects are fully informed and usually paid, but they comes to those of other carriers (external benchmarking), quickly revert to driving in their normal manner. This per- or to track them in relation to past performance or to goals mits observation of driving behavior and traffic events as (internal benchmarking). they naturally occur. Correlation--The degree of association or predictability Navigation--Way-finding, generally in the context of a par- between two variables (e.g., height and weight) among ticular A-to-B trip. the same group of subjects (e.g., drivers). Odds ratio--A statistic often used to quantify relative risk Correlation coefficient--A statistic summarizing direction or occurrence of an outcome for two different situations and degree of association. Correlation coefficients range or groups. An odds ratio greater than 1.0 implies over- from -1.0 (a perfect inverse relation) through zero (no sta- involvement (e.g., in driving incidents), whereas an odds tistical association) to +1.0 (a perfect linear relation). ratio less than 1.0 implies under-involvement. Critical Reason (CR)--In the LTCCS, the human, vehicle, or Response bias--The tendency, likely strong in the current environmental failure leading to the Critical Event and thus surveys, for respondents to be more committed and inter- to the crash. The immediate or proximal cause of a crash. ested in the topic than those not responding. Because of Deadheads--Empty backhaul trips. response bias and other factors, the surveys in this project Detention--Excessive driver delays associated with truck should not be considered representative of larger groups loading and unloading. (e.g., all motor carrier safety managers). Diversion--The practice of avoiding freeway tolls by choosing Risk avoidance--In this report, refers to operational practices alternative, untolled routes, which often are undivided high- that deploy vehicles and drivers efficiently and with safety ways with more traffic interaction and higher crash risks. benefits; includes safety-conscious routing (e.g., maximizing Exposure--Vehicle-miles traveled (VMT), hours driving, freeways, minimizing peak hour driving, assigning familiar or other denominator to determine crash rates. Exposure routes) and similar deployment strategies. data are essential for determining relative risk for different Risk factor--Any prior factor (driver, vehicle, environment, drivers, vehicle types, and driving situations. carrier) that affects the probability of a crash. Haddon Matrix--A framework for understanding and design- Risk reduction--In the context of this report, refers to con- ing crash reduction strategies. The 3 3 matrix juxtaposes ventional carrier safety efforts to improve the safety per- time frame (i.e., pre-crash, crash, and post-crash) and agent formance of individual drivers and vehicles. This usually (i.e., human, vehicle, environment). Expansions of the involves making company investments in proven interven- Haddon Matrix account better for the complexities of CMV tions such as improved driver selection, training, manage- transport. ment oversight, or vehicle safety equipment; contrasted Higher-Productivity Vehicles (HPVs)--Vehicles with Gross with risk avoidance, defined earlier. Vehicle Weight Ratings (GVWRs) of more than 80,000 lb, Routing optimization--Improvements in the efficiency of the maximum size of standard tractor-semitrailers; includes an overall pickup and delivery sequence, as in a full driver Longer Combination Vehicles (LCVs). tour-of-duty or multiday trip (Bennett 2009). Likert scale--Common survey technique in which answer Speed limiters--Electronic controls that limit the top pow- choices are presented as numeric rating scales, often with ered speed of vehicles; also called speed governors. five choices numbered from 1 to 5. Speed paradox--Although excessive speed is the biggest Mean--The arithmetic average score in a group of scores, single proximal cause of crashes, there is generally less computed by adding all the scores and dividing the sum by crash risk at higher travel speeds across the normal ranges the number of cases. of speed (i.e., not including overspeeding). The speed para- Median--The middle score in a group of scores. The point dox demonstrates the overall positive association between or score that divides the group into two equal parts. The travel efficiency and safety. median is also known as the 50th percentile. Telematics--General term encompassing onboard sensors, Naturalistic driving--Safety research in which vehicles are networks, software, GPS, and wireless communications that instrumented with video camera and various dynamic sen- are becoming commonplace in today's commercial vehicles.