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Frequently Asked Questions

The Frequently Asked Questions (FAQs) are questions and answers about Compliance, Safety, Accountability (CSA) that the Federal Motor Carrier Safety Administration (FMCSA) compiled to assist the public. As questions come in through the website, FMCSA adds them to the database along with their answers. If you do not see your question or topic addressed, please contact us by submitting a feedback form. We will respond to you directly and consider your question for inclusion in the FAQs.

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  1. What is a Power Unit (PU) and how does the Safety Measurement System (SMS) use this information? Answer

    PUs are recorded in the motor carrier registration data (MCS-150) on file. PUs may include vehicle types such as trucks, tractors, hazardous material tank trucks, motor coaches, and school buses.

    The number of PUs a carrier has is used in part to account for each motor carrier's level of on-road exposure when calculating the Unsafe Driving and Crash Indicator Behavior Analysis and Safety Improvement Categories (BASICs). SMS calculates the average number of PUs for each carrier by using (1) the carrier's current number of PUs, plus (2) the number of PUs the carrier had 6 months ago, plus (3) the number of PUs the carrier had 18 months ago divided by 3. The average PUs numbers along with annual Vehicle Miles Traveled information are used as a measure of exposure to estimate the number of PUs operated over a 24-month time period when traffic enforcement violations (used in the Unsafe Driving BASIC measure) or reportable crashes (used in the Crash Indicator) could have occurred. Due to the potentially significant changes in exposure of individual carriers over the course of 24 months (via downsizing, mergers, etc.), an average number of PUs provides a more accurate estimate of vehicle exposure for carriers that have updated their MCS-150 motor carrier registration information.

    Please refer to the SMS Methodology document for additional information and an example of the average PU calculation.

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