Total intermodal shipments in the U.S. and Canada rose 2% over last year’s first quarter volumes despite port congestion issues that impacted international container traffic, according to new figures from the Intermodal Association of North America.

Domestic intermodal loads grew 4.5%, buoyed by domestic containers, which rose 6.5%.

“Monthly first quarter results were uneven due to the issues on the West Coast,” said Joni Casey, president and CEO of IANA. “Despite February’s challenges, however, we still saw some overall quarterly growth, led by big boxes in regions less affected by port congestion.”

According to IANA, domestic intermodal results were particularly impressive in view of the challenges facing the import sector. A significant share of the freight carried by domestic intermodal is trans-loaded from 40-foot containers that come through a port. First quarter volumes exceeded the 5.1% gain recorded in the fourth quarter of 2014.

Regional traffic growth remained tied to port issues, notwithstanding the relative strength of domestic intermodal. Volumes were down in the Southwest, which saw a 5.7% decline over the first quarter 2014. The Southeast surged 9.9% due to increases in both domestic and international containers. Western Canada posted the strongest growth rate of any region, jumping an exceptional 10.6% in the first quarter.

The seven largest volume corridors also varied according to their exposure to port disruptions. While lanes that included the Southwest were down, the intra-Southeast continued to be an intermodal powerhouse. Intermodal shipments in that lane jumped 16.5% from the fourth quarter of 2014. Overall, high-density lanes, which accounted for 64.5% of total volumes, saw a minimal decline of 0.9% in the most recent quarter

Intermodal marketing companies reported 3% growth in the first quarter, laying the groundwork for an even stronger performance in the coming months, according to IANA. Intermodal and highway loads jumped 3.2% and 2.6%, respectively. IMC highway gains were significant enough to push revenues up 1%, compared to first quarter of 2014.