Rail Traffic Reverses Hard: AAR's Week 36 Data Show Intermodal Down 4.1%, One Week After an 18% Gain

The Association of American Railroads' Weekly Rail Traffic report for the week ending Sept. 12, 2026 shows U.S. carloads down 3.3% and intermodal units down 4.1% from the same week a year earlier. That's a sharp reversal from the prior week, when Seven Stars reported intermodal volume up 18% year over year for the week ending Sept. 5 — a swing of more than 20 points in one week that has more to do with the Labor Day comparison base than with a change in underlying demand.

Year-to-date, the picture is still positive: carloads are up 2.7% and intermodal up 4.0% through week 36, both comfortably ahead of where 2026 started. The single-week numbers are the ones that move headlines; the year-to-date numbers are the ones that describe the market a drayage provider or intermodal marketing company is actually operating in.

What moved, and what it means

The commodity breakdown is where this week's report earns its keep. Motor vehicles and parts fell 18.8% for the week — the steepest single-commodity decline in the report — though the year-to-date figure for autos is a much milder -0.9%, meaning this week's drop is a dip against a base that had otherwise held roughly flat. For rail-served auto plants and the drayage and intermodal capacity that serves them, a week like this is a signal to check whether it's a single OEM's scheduled downtime or a broader production pullback before adjusting equipment commitments.

Chemicals fell 9.2% for the week but remain up 2.1% year-to-date — the same pattern as autos, a weekly air pocket inside a positive trend rather than a reversal of it. Petroleum and products, by contrast, gained 6.5% for the week and are up 7.5% year-to-date, a steadier climb that tracks with elevated refined-product movement amid this month's fuel-price spike (see Seven Stars' companion diesel coverage). Grain led the report at +17.3% for the week and +12.6% year-to-date, consistent with the seasonal harvest ramp — shippers needing hopper-car capacity into October should expect competition for equipment to build from here, not ease.

Coal continues its slow bleed, down 3.7% for the week and 1.8% year-to-date, the only major commodity category negative on both timeframes.

The forwarder read

Two things worth acting on rather than just noting:

First, don't extrapolate from a single week in either direction. The move from +18% to -4.1% intermodal in seven days is a reminder that late-August and early-September weekly comparisons are distorted by where Labor Day falls relative to the reporting week — AAR itself flags that its figures are provisional and subject to revision for up to a year. Anyone building a Q4 capacity plan off one week's print, positive or negative, is building it on noise.

Second, the diverging weekly-versus-YTD pattern in autos and chemicals is worth a second look before it's dismissed as noise, too. If next week's report shows autos still negative on a week-over-week basis, that's the point at which a one-week dip starts to look like the beginning of a trend, and drayage capacity planners serving automotive corridors should treat it as an early signal rather than wait for the year-to-date number to catch up.