The oil train that crashed and burned after colliding with a derailed train near Casselton, N.D., on Dec. 30 spilled 400,000 gallons of crude, U.S. investigators said Monday in a preliminary report on the accident.

The two BNSF Railway Co. trains were traveling well under the permitted speed on parallel tracks outside Casselton, said the report from the National Transportation Safety Board (NTSB).

NTSB investigators offered no conclusion about why the westbound grain-bearing train derailed. Final reports on the agency's investigations typically take months.

U.S. Sen. Amy Klobuchar, D-Minn., on Monday called for a separate inquiry by the Senate Transportation Committee focused on tank car standards. She said the committee should review recent oil train explosions, including the North Dakota crash and an accident last July in Lac Mégantic, Quebec, that killed 47 people and incinerated part of the town. She also wants to look into the Dec. 5 derailment of a Canadian National iron ore train in Two Harbors, Minn., in which two workers were injured.

In a letter to committee Chairman John Rockefeller, D-W.Va., Klobuchar said the recent crashes "have raised concerns even among those very Americans who depend on rail for jobs, commerce and transport." Klobuchar serves on the committee.

North Dakota, now the No. 2 oil-producing state behind Texas, lacks sufficient pipelines to carry away its growing Bakken region output. More than two-thirds of the state's crude oil is shipped by rail, and many of the 100-tanker oil trains past through the Twin Cities on BNSF and Canadian Pacific tracks.

North Dakota Gov. Jack ­Dalrymple on Monday expressed support for more-stringent standards for tank cars. Last week, the state's three-member congressional delegation also urged federal regulators to move quickly to address safety issues.

"It's very clear that we need tank cars with improved safety features for the transportation of Bakken crude oil," Dalrymple said in a statement after speaking to BNSF CEO Matt Rose about rail safety.

Safety appeal ignored

After a deadly 2009 ethanol train crash and fire in Illinois, the NTSB recommended upgrading rail tank cars to make them more resistant to punctures and to improve other safety features. But the U.S. Pipeline and Hazardous Materials Safety Administration has not yet proposed regulations to address those concerns.

In the preliminary report on the North Dakota accident, the NTSB said the eastbound train with 106 oil tankers collided with a derailed car from the grain train that had landed on the eastbound track.

The oil train had been traveling at 43 miles per hour and struck the derailed car at 42 mph, the report said. The speed limit for freight trains in that area is 60 mph.

The grain train was traveling at 28 mph when its emergency brakes were engaged, but the report did not say whether that happened before or during its derailment.

The collision sent the oil train's two locomotives and 21 other cars, including 20 tankers, off the tracks.

Eighteen of the tankers were punctured and some exploded in fireballs that were visible for miles. Authorities evacuated 1,400 residents of Casselton as a precaution. No one was injured, including crew members from both trains who sprinted away before the explosions.

The NTSB estimated damage from the accident at $6.1 million. The trains were cleared and traffic resumed on the tracks near Casselton, 20 miles west of Fargo, on Jan. 2.

The NTSB said it had taken a broken axle and two wheels from the accident to Washington for deeper analysis, but it didn't specify from which train the parts came. • 612-673-7090 • 612-673-4241