North American truckload volumes on the noncontract, or "spot" market, rose 34 percent last month compared to February volumes, a surge typical for the early spring, which is one of the year's peak periods, according to a monthly index issued today by DAT Solutions, a research consultancy.

By comparison, March volumes declined 28 percent from March 2014 levels, DAT said. Last year's severe weather in the first quarter resulted in unprecedented volume surges later in the quarter as tonnage snapped back violently after being restrained due a dramatic reduction in rig supplies. The busy spring freight season usually begins in late March.

By equipment type, freight volume increased sequentially—by 34 percent for dry vans, 41 percent for flatbeds, and 20 percent for refrigerated, or "reefer," trailers, DAT said. Rates last month rose sequentially for all equipment types, with van rates up 2.5 percent, flatbeds up 2.8 percent, and reefer equipment up 1.7 percent, DAT said.

Compared to the extraordinary market conditions of March 2014, year-over-year freight volume by equipment type declined 19 percent for vans, 42 percent for flatbeds, and 1.3 percent for reefers. Rates increased, however, with van rates up 2.5 percent, flatbed rates up 6.9 percent, and reefer rates 6.4 percent. Monthly average rates have increased year-over-year for more than 20 consecutive months, according to DAT figures.

Though estimates vary, it is believed that spot market volumes account for between 15 and 20 percent of all truckload freight moving in the U.S. Spot pricing trends are important in that they often influence the outcome of the much larger market for truckload shipments moving under contract. In 2014, intermediaries and carriers across North America listed more than 120 million loads and trucks on DAT's load board network.

Mark Montague, an industry pricing analyst for DAT, said in an e-mail that spot market volumes are generally solid, while rates are mostly stable for van freight and increasing at a normal pace for flatbed and refrigerated freight. Montague said, however, that there is more capacity in the market than he expected, adding that most regions are able to procure trucks. Northern Alabama currently has the highest demand for van equipment, while demand in Chicago is unusually weak, Montague said. Flatbed capacity, driven by increased warm-weather demand for construction materials and equipment, is showing the most tightness, he said.

Reefer demand has been hit by a downturn in produce production in California and Florida, Montague said. Reefer equipment is in greater demand to haul meat and processed foods than to transport produce, he said.

Tucson is the country's top current produce market, Montague said. Demand there is being influenced by activity at the border crossing city of Nogales, Ariz., where a great deal of produce grown on Mexico's Pacific coast enters the U.S., he said.