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
by submitting a feedback form. We will respond to you directly and consider your
question for inclusion in the FAQs.
The FAQ area has recently been enhanced. Users can now search FAQs by stakeholder
group, topics (displayed on the left side of the page), or by entering a keyword
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What is a Power Unit (PU) and how does the Safety Measurement System (SMS) use this
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.