Power Units
The industry-standard measure of fleet size, counting only vehicles with an engine — trucks and tractors, not trailers. When someone says a carrier has 50 trucks, they mean 50 power units. CarrierOk reports power units separately from trailers via the total_power_units field, sourced from MCS-150 filings.
Definition
Power units are the industry-standard metric for measuring fleet size in the trucking industry. A power unit is any commercial motor vehicle with its own engine — this includes tractors (semi-trucks), straight trucks, buses, and other self-propelled CMVs. Trailers are explicitly excluded because they don't operate independently and many carriers use trailer pools or interchange trailers with other carriers. When the industry, FMCSA, or insurers reference 'fleet size,' they mean power units. The MCS-150 form breaks fleet size into owned power units and term-leased power units, which together constitute the total fleet. This distinction matters because owned equipment represents capital investment and maintenance responsibility, while leased equipment may indicate owner-operator relationships with different risk profiles. Fleet size is a core underwriting variable — it determines premium base, establishes peer groups for BASIC percentile comparison, and influences operational complexity assumptions. Common fleet size segments include: single owner-operator (1 unit), small fleet (2-10 units), mid-size fleet (11-100 units), and large fleet (100+ units). CarrierOk reports total_power_units, owned_tractors, and term_leased_tractors as separate fields, enabling precise fleet composition analysis.
Why It Matters
For Underwriters
Power unit count is the primary exposure base for commercial auto policies — it determines premium, establishes the carrier's peer group for BASIC comparison, and signals operational complexity.
For Brokers
Fleet size indicates a carrier's capacity and operational scope — a 3-truck carrier accepting loads across 48 states is a different risk than a 200-truck carrier doing the same thing.
For Developers
Use total_power_units as the denominator for per-unit metrics (crashes per power unit, violations per power unit) to normalize safety data across carriers of different sizes.
In the API
/v2/profileRelated Fields
total_power_unitsowned_tractorsterm_leased_tractorstotal_trailerstotal_driversFrequently Asked Questions
What is a power unit in trucking?
A power unit is any commercial motor vehicle with its own engine — tractors, straight trucks, and other self-propelled vehicles. Trailers are not power units because they don't operate independently. When the industry references fleet size, it means power units. A carrier with '50 trucks' has 50 power units, regardless of how many trailers they own or lease.
Why do we count power units instead of total vehicles?
Power units are the standard because they represent the actual operational capacity and risk exposure of a fleet. Trailers are excluded because they're passive equipment — many carriers use shared trailer pools, interchange trailers with partners, or operate with far more trailers than tractors. Counting trailers would inflate fleet size measurements and distort peer comparisons. FMCSA, insurers, and the industry all use power units as the standard.
What is the difference between owned and leased power units?
Owned power units are vehicles the carrier holds title to and is directly responsible for maintaining. Term-leased power units are vehicles leased from another party for a defined period, often associated with owner-operator arrangements where the driver provides the truck. The distinction matters for insurance because it affects maintenance responsibility, driver relationship type, and the carrier's capital structure.
Related Terms
MCS-150 (Motor Carrier Identification Report)
A biennial update form that motor carriers must file with FMCSA reporting fleet size, driver count, mileage, cargo types, and contact info. An MCS-150 older than 2 years is a compliance red flag. CarrierOk tracks MCS-150 filing dates and flags stale filings as a risk signal.
CDL (Commercial Driver's License)
A license required to operate commercial motor vehicles in the United States, classified as Class A (combination vehicles over 26,001 lbs), Class B (single vehicles over 26,001 lbs), or Class C (hazmat/passenger). CarrierOk reports total CDL drivers per carrier as a fleet composition signal.
Safety Rating
A rating assigned by FMCSA after a compliance review: Satisfactory, Conditional, or Unsatisfactory. An Unsatisfactory rating can trigger an out-of-service order. However, most carriers have never been reviewed and carry no rating — absence of a rating does not indicate safety. CarrierOk includes safety rating status in carrier profiles.