Where America's Trucks Go — and Why It Changes Every Season
We analyzed 9.5 million FMCSA roadside inspection records from August 2022 through February 2026 to map how trucking capacity migrates across the United States. When a carrier domiciled in one state gets inspected in another, that's one observation of an interstate flow. Aggregated across millions of records, these flows reveal a recurring seasonal heartbeat in American freight.
Key Findings
- •Trucking capacity peaks in May (253K inspections, 108K unique carriers) and troughs in February (177K inspections, 79K carriers) — a 43% seasonal swing.
- •Capacity is most geographically dispersed in September and most concentrated in January, when trucks retreat to Sun Belt states.
- •Arizona’s reefer share swings from 25% in winter to 19% in late summer — tracking the Yuma produce harvest — the largest equipment-specific seasonal shift of any state.
- •Illinois, Texas, and California are the three dominant origin hubs, collectively generating more outbound flow than the next 10 states combined.
- •Mega fleets (100+ trucks) operate 660+ miles from home on average, while owner-operators stay within 375 miles — a nearly 2x distance gap.
The Seasonal Pulse
Freight doesn't flow evenly across the year. Our data shows a pronounced annual cycle: the system wakes up in March as carriers return to the road after winter, peaks in May at 252,709 inspections and 107,663 unique carriers, then gradually contracts through the fall. February is the quietest month with just 177,394 inspections — 30% below the May peak.
But it's not just volume that changes — it's geography. We measured market concentration using the Herfindahl-Hirschman Index (HHI) across all 50 states. In September, capacity is most evenly spread (HHI 0.048, with 34 states each holding at least 1% of national activity). By January, the index climbs to 0.057 as capacity retreats south — the top 5 states absorb nearly 40% of all activity, up from 36% in the fall.
This "winter concentration" effect means carriers physically migrate toward warmer states during the off-season, then spread back out as spring freight picks up. Play the seasonal animation above to watch this cycle unfold month by month.
Reefer Follows the Harvest
Select Reefer in the equipment filter above to see one of the clearest seasonal signals in American freight. Refrigerated trailers don't just go where freight is — they follow the agricultural calendar, and the map lights up in orange and blue as reefer concentration surges and contracts along produce corridors.
Arizona shows the most dramatic swing: reefer trailers account for 25% of all inspections in January — driven by the Yuma winter lettuce and vegetable harvest — then drop to 19% by September, a 6 percentage-point seasonal shift. This pattern is statistically significant (chi-squared test, p < 0.001) and repeats every year in our dataset.
Other states tell their own reefer stories: Idaho peaks at 26% reefer share in early spring (potato and dairy shipments) before dropping to 18% in summer. Washington runs 18% reefer in winter (cold-storage apple exports) and falls to 15% in June. Even Georgia shows a July reefer peak at 9% — peach season — before contracting in the fall.
Meanwhile, dry van remains the baseline at 40–49% share nationally, and flatbed trailers track construction activity, showing their strongest deviation in states with seasonal building cycles.
The Dominant Corridors
Not all interstate flows are equal. The heaviest corridor in our dataset is California → Arizona, averaging 1,224 inspections per month with over 1,000 unique carriers making the crossing. Close behind are Texas → New Mexico (1,159/mo) and California → New Mexico (1,026/mo) — reflecting the I-10 and I-40 freight corridors that connect the West Coast to the interior.
Three states dominate as origin hubs: Illinois generates the most outbound flow in the country (driven by Chicago's role as a national freight crossroads), followed by Texas and California. On the destination side, California flips to the #1 receiver of inbound capacity — carriers from Ohio, Illinois, Washington, and Texas all converge on the state. Click any state on the map above to explore its specific inbound and outbound patterns.
Fleet Size Changes Everything
How far a carrier operates from home is strongly correlated with fleet size. Owner-operators (single-truck carriers) average 376 miles from their domicile state with 48% of their inspections occurring outside their home state. Mega fleets (100+ trucks) average 668 miles from home with 79% of inspections out-of-state — a nearly 2x distance gap.
This gap holds across every month of the year but subtly shifts: in January, owner-operators venture slightly further from home (376 mi) compared to July (371 mi), likely reflecting the seasonal pattern of following freight to wherever it is available during the slower winter months. Large and mega fleets show a similar but smaller seasonal compression.
Methodology
This analysis is based on 9,501,412 roadside inspection records published by the Federal Motor Carrier Safety Administration (FMCSA) from August 2022 through February 2026. Each record includes the inspected carrier's DOT number, domicile state, inspection state, date, equipment type, and fleet size.
A "flow" is defined as an inspection where the carrier's domicile state differs from the inspection state. Seasonal baselines are computed by averaging each origin-destination pair across all available years for each calendar month. Deviations represent the percentage difference between a given month's flow volume and its seasonal baseline for that specific O-D pair. Equipment shares are calculated as the fraction of inspections involving each trailer type at a given state and month, with statistical significance assessed via chi-squared tests against the statewide annual baseline.
Geographic concentration is measured using the Herfindahl-Hirschman Index (HHI), computed from each state's share of national inspection volume. An HHI of 0.02 indicates perfect dispersion across 50 states; higher values indicate concentration.