A preliminary report released Thursday by federal investigators blames Union Pacific Railroad for the oil train derailment earlier this month in the Columbia River Gorge.

"Union Pacific's failure to maintain its track and track equipment resulted in the derailment," read the findings from Federal Railroad Administration.

The findings confirm what the railroad company has previously acknowledged: Broken bolts led to the train cars being pushed off the tracks.

Four oil-tank cars burned for 14 hours after after 16 tanks cars derailed near the town of Mosier. The train was traveling at 25 miles per hour, 5 miles per hour less than the speed limit in the area.

Federal investigators also found that a more modern braking system would have led to a less severe derailment.

"We're talking about upgrading a brake system that is from the Civil War era," Federal Railroad Administrator Sarah Feinberg told the AP. "It's not too much to ask these companies to improve their braking systems in the event of an accident so fewer cars are derailing."

The company has said they will begin running oil trains through the Gorge later this week—over the objections of county, city and state officials that have raised alarms.

Federal officials are still weighing a punishment for the railroad.

UPDATE, 1:01 pm: Union Pacific spokesman Justin Jacobs defended the company's safety record and disputed that the conclusion that the company was using an inadequate braking system.

"Union Pacific's rail fastening system, which includes lag bolts, has an outstanding history of safety and reliability," Jacobs says. "Since the June 3 derailment in Mosier, we are enhancing our regular inspection process. As part of our ongoing track renewal program, lag bolts with this fastener system are being replaced with rail spikes, which provide higher levels of fault detectability in standard inspection processes."

Jacobs also argues that a new brake system would not have reduced the scale of the crash.

"Electronically controlled pneumatic (ECP) braking technology has yet to meet service reliability standards," he says. "The train involved in the Mosier accident was equipped with distributed power, which has a braking capacity nearly identical to ECP. We do not believe ECP brakes would have resulted in fewer rail cars derailing."