Domestic container volume gained a "remarkable" 14.9% in the first quarter compared to a year ago, according to the Intermodal Association of North America's Intermodal Market Trends & Statistics report.

Although a rebounding economy helped boost volume, much of Q1's domestic intermodal gains can be attributed to market share growth, as trucking capacity was tight during the quarter and diesel prices resumed their rise after softening in Q4 2011. Domestic container gains were biggest in the East, where intermodal faces more competition from trucking.

International volume increased 2.9%, a gain that on the surface pales in comparison to the strength of domestic containers. Yet a closer look at the numbers suggests that international intermodal's Q1 performance was actually much stronger than the year-over year growth rate would suggest, according to IAA analysts. International intermodal shipments advanced 9.6% in Q1 2011. This strong performance was driven by the need for retailers to replenish inventories after a better-than-expected holiday sales season. The booming growth in the first quarter of 2011 has made comparisons more challenging for Q1 2012.

Trailer-on-flatcar shipments fell 6.9% year-over-year in the quarter, and again, part of the decline is due to stronger comparisons - in Q1 2011, trailers gained a robust 7.4%. However, with containers close to 90% of the market, overall intermodal volume gained an impressive 5.8% during this quarter. Domestic container gains may slow in coming months as comparisons to the previous year become more competitive, but international growth will likely accelerate. Overall, container shipments should maintain their strong growth rate through the year.