If you've ever seen a mile-long freight train and wondered how safe those tank cars were, know this: they are about to get a lot safer.

After recent accidents caused oil tank cars to explode, officials realized it was time to update railroad regulations and give these old tanks an upgrade.

The U.S. and Canada have devised new standards, requiring tougher railroad cars for carrying flammable liquids, and a retrofit plan for the older ones.

Since 2008, the number of crude oil shipments by rail in North America has increased by 4,000 percent, but safety regulations were unchanged.

U.S. Transportation Secretary Anthony Foxx says even a 99.9% safety record isn't good enough. He said the U.S. and Canada "have to strive for perfection" in preventing all tank car crashes and fires.

(WATCH the video below and READ more at NBC News) Photo by Sam Beebe, Ecotrust – Story tip by Carilyn

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