AAR Week 39, the latest in the Association of American Railroads' weekly traffic series covering a seven-day period ending in late September, shows US rail traffic volume still climbing on an overall basis, according to the headline summary published by Railway Age.

The Association of American Railroads, the Washington-based trade body representing North American freight railroads, publishes weekly carload and intermodal traffic data every Thursday. The release aggregates submissions from the Class I freight railroads that operate across the United States.

The reporting group includes BNSF Railway, Union Pacific, CSX Transportation, Norfolk Southern, Canadian National, and Canadian Pacific Kansas City — the merged entity formed when Canadian Pacific completed its acquisition of Kansas City Southern in April 2023. Short-line and regional carriers contribute through AAR's secondary reporting channels, though their volumes are presented separately and excluded from the headline Class I total.

What the weekly release measures

AAR's weekly bulletin breaks total volume into roughly 20 commodity categories. Grain, coal, chemicals, motor vehicles and parts, metallic ores, forest products, and intermodal containers and trailers typically account for the majority of carloadings.

The intermodal segment is reported as a unit count rather than a tonnage figure, since containers carry varied cargo and weights fluctuate widely. AAR publishes the underlying year-on-year percentage changes for each commodity group and for the total, allowing analysts to decompose the headline number into its component parts.

The Week 39 headline characterizes the trend as "still climbing, overall." That wording points to combined carload and intermodal volumes tracking higher than the same week a year earlier. The "still" qualifier signals a continuation of an earlier trend rather than a fresh acceleration.

Why the rolling average matters more than any single week

AAR's release also includes a four-week rolling average, designed to smooth the volatility that comes from Labor Day timing, weather disruptions, and the September 30 fiscal year-end effect for Canadian carriers.

Analysts and rail industry economists typically cite the rolling average when characterizing the trend, because a single week can move sharply in either direction depending on the calendar. The "still climbing" framing suggests the moving average continued to point upward through Week 39, reinforcing the view that the underlying demand environment remains positive.

What the trend signals for operators and shippers

A consistent week-over-week rise in the AAR total supports the case that rail demand is holding up against a mixed industrial backdrop. Manufacturing output, port throughput, and agricultural shipments all feed into the rail volume figure, making it a useful proxy for the broader goods economy.

For Class I carriers, rising volumes feed directly into operating leverage. Much of the cost base — crews, locomotives, fuel, and track capacity — is fixed in the short term, so additional volume flows through the network with relatively low marginal cost. That dynamic supports the operating ratio improvements that Class I management teams typically target.

Shippers watch the AAR release as a proxy for capacity tightness. Sustained growth tends to pull forward contract negotiations and can tighten equipment availability in the intermodal segment, particularly through the West Coast gateways at Los Angeles and Long Beach, which handle a disproportionate share of US containerized imports.

Looking ahead

The next AAR weekly release, covering Week 40, will capture the first full week of October. It will provide the next data point in the Q4 sequence and the first reading after the federal fiscal year-end on September 30.

Carriers, shippers, and analysts will be watching whether the "still climbing" pattern continues, plateaus, or reverses as the peak shipping season enters its final weeks and the autumn grain harvest builds across the Midwest and Plains.