Truckload linehaul contract rates in December rose 7.4 percent from the same period a year ago, according to data released today by two firms that publish a monthly rate-tracking index. Gains of this magnitude, the firms said, will extend at least through the first quarter.

At the same time, an index of rail intermodal per-mile costs—which reflect rates paid by intermodal users—rose in December by only 1.5 percent year-over-year, one of the weakest months for intermodal pricing in an otherwise decent year. The firms, freight audit and payment company Cass Information Systems and investment firm Avondale Partners, forecast that intermodal rates will decline in 2015 as the recent dramatic drop in diesel fuel prices leads intermodal shippers to convert their loads back to truckload.

Avondale said in a statement that it predicts a 4- to 9-percent average increase in truckload contract rates in 2015. The actual increase for each carrier will depend on the extent of the increases it obtained last year and when the increases took effect, it said. Contract pricing, which applies to more than 95 percent of the freight hauled by publicly traded carriers, has been rising since the conclusion of a "drawn-out" bidding season, Avondale said. The strong truckload pricing environment is being driven by an "extraordinarily tight" market for rig capacity—largely due to a shortage of qualified truck drivers—and by increasing freight demand, the firm said. Although not mentioned in the Cass-Avondale statement, other sources have noted that driver wage increases are also being passed through to users in the form of higher rates.

By contrast, intermodal contract rates have begun to slow from the 3-percent year-over-year pace of increases achieved through much of last year's second half, Avondale said. The firm acknowledged that the extent of the conversion from domestic intermodal to over-the-road services would depend on the availability of truckload capacity. Still, a drop of more than 15 cents per mile in truckload fuel surcharges since oil and fuel prices began to fall last summer will challenge demand and pricing power for domestic intermodal services, Avondale said.

The projected declines in intermodal pricing come as the four main U.S.-based east-west railroads—CSX Corp., Norfolk Southern Corp., Union Pacific Corp., and BNSF Railway—invest billions of dollars to build out intermodal networks. Intermodal service reliability has suffered for the past year due to terrible weather in 2014's first quarter that paralyzed the nation's main rail hub in Chicago, strong demand from producers of other commodities, and a general shortage of crews, trains, and infrastructure.

One of rail intermodal's chief selling points is its fuel efficiency relative to over-the-road trucking. However, with the spot price of a barrel of West Texas Intermediate (WTI) crude oil at $44.45, its lowest price in six years, and with the average nationwide on-highway price of a gallon of diesel fuel at its lowest point since March 2010, the rails' message has, for the near future at least, been diluted.