Intermodal rail traffic in the U.S. during September hit the second-highest weekly average of any month on record, according to new figures from the Association of American Railroads.

The weekly average of 256,881 intermodal units also occurred as September saw the three highest-volume intermodal weeks in history for U.S. railroads last month. Only the Labor Day holiday prevented it from being the highest-volume intermodal month in history.

Intermodal traffic in September totaled 1,027,522 containers and trailers, up 4.4% compared with September 2012.

For the first 39 weeks of 2013, U.S. railroads reported cumulative volume of 10,940,538 carloads, down 0.9% from the same point last year, and 9,547,764 intermodal units, up 3.7% from last year.

Total U.S. traffic for the first 39 weeks of 2013 was 20,488,302 carloads and intermodal units, up 1.2% from last year.