US intermodal rail traffic jumped 10.4% year-over-year in week 40, and domestic carload volume rose 3.4%, combining for a 7.2% increase in total US rail traffic, according to Association of American Railroads data cited by rail reporter Bill Stephens. The figures mark the latest proof that American rail freight is running a broad-based boom rather than a handful of bright spots.

North America as a whole followed suit: carload volume climbed 2.6% and intermodal 9.1%, for a combined gain of 5.9% against the same week a year earlier.

For carriers and shippers, the reading matters because it reinforces a durable industrial expansion. The AAR's September and third-quarter Rail Industry Overview, released the day before the weekly data, found that 17 of 20 carload categories posted year-over-year gains in September.

Where is the growth coming from?

Western railroads led the intermodal surge. BNSF moved up 12.5% for the week, while Union Pacific jumped 19.4% — a performance Stephens attributed to record container volumes moving through the ports of Los Angeles and Long Beach and now pumping through the broader economy.

Eastern carriers also posted solid numbers: CSX gained 8.9% and Norfolk Southern rose 5.4%.

Commodity detail points the same direction. Motor vehicles and parts, a category that has lagged through 2025, rebounded sharply at 9.4% in week 40. Metallic ores and metals continued double-digit year-over-year growth, consistent with what the AAR described as manufacturing expansion that "took off at the start of the year" and "appears to be increasingly durable."

Excluding coal and grain, carload volume was up 5.6% for the week. Coal slipped 2%, while grain edged up just 0.5%.

One commodity stands above the rest. Chemicals traffic — the second-largest carload commodity — set a September record and is on pace for a new annual record, according to the AAR.

Why is intermodal winning share?

The economics explain the momentum. Diesel prices are elevated, trucking capacity is tight, and rail service is holding up despite the volume surge.

"It's nothing but tailwinds for intermodal due to the cost savings, partly related to the surge in diesel price, the tight trucking capacity. And the third ingredient there is that rail service seems to be holding up for the most part despite this volume surge," Stephens said.

For shippers, that combination means intermodal continues to offer a price hedge against truckload markets. For carriers, it means volume growth without — so far — the service breakdowns that have historically undermined rail's pitch to freight buyers.

What could slow the boom?

The AAR flagged one risk: if diesel prices remain elevated long enough, consumer spending could soften. For now, the consumer side holds up — consumer goods spending rose 2.7% in August, according to the AAR.

Stephens noted that inflation data is beginning to broaden beyond gasoline into food prices, a trend worth watching for consumer-dependent freight segments.

What about the UP–NS merger review?

On the regulatory front, parties are filing their intent to participate with the Surface Transportation Board in the Union Pacific–Norfolk Southern merger review.

STB board member Richard Kloster drew attention when the board accepted the merger application, calling for stronger data and better arguments — comments Stephens characterized as likely reflecting broader board sentiment rather than a political maneuver.

Further detail is expected when both railroads hold earnings calls. Questions are anticipated on the conditions being sought by other railroads and on Kloster's remarks.

The near-term trajectory, on the AAR's own numbers, points to continued strength: record chemicals volumes, durable manufacturing growth, and West Coast port containers still feeding the network — with fuel prices the variable most likely to decide how long the tailwinds last.

By Elena Vasquez, Waybill Wire