Despite derailments, freight train safety is improving

Oil, chemicals and other goods are shipped across the country on a network of 140,000 miles of track. This year alone, freight railroads are expected to spend a record $29 billion upgrading rails and purchasing new locomotives and cars.

In the first four months of 2015, there have been seven train derailments releasing hazardous materials. It's happened at least 58 times since 2012.

But overall, the Federal Rail Administration says freight derailments are down nearly 47 percent since 2005.

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"The challenge in railroad safety is that there's no one cause that you can attack," says Dr. Allan Zarembski, who teaches train safety at the University of Delaware.

"We tend to look at where are the larger concentrations of derailments and what technology is going to help find the derailment causes before they actually result in a derailment," Zaremski tells CBS News.

There is growing concern about the sometimes mile-long oil trains hauling volatile crude from North Dakota's oil fields.

The amount of crude transported by rail has jumped 4,000 percent since 2008. At least five times this year, oil trains have derailed and caught fire.

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National Transportation Safety Board Chairman Christopher Hart has expressed concerns about the tank cars used to carry crude.

"Unfortunately we're using the same cars to move crude oil that we use to move corn oil," Hart says. "That is simply not acceptable."

The Association of American Railroads president and CEO Edward Hamberger says the industry's safety record is sound.

"The percentage is amazingly low -- 99.995 percent of cars get across our network without an accident," Hamberger says. "We won't be satisfied until we can get it to 100 percent safety, but right now, we're at 99.995."

The Department of Transportation has issued new stronger guidelines for rail tanker cars that haul crude, but it'll be up to five years before all cars are required to meet that standard.

Railroads are also required to install technology aimed at stopping derailments by the end of the year.