By Ezra Kaplan

A 21 percent jump in the number of tank cars of crude oil traveling by U.S. rail in 2014 over 2013 represents a new record total of nearly half of a million cars of crude, according to the Association of American Railroads.

A total of 493,126 crude oil tank cars moved through the country last year. The new numbers reflect the ongoing domestic oil boom as well as a slowing of growth. The growth was significantly less than in the previous four years. Tank car numbers skyrocketed 255 percent in 2012 compared to 2011.

“The reduced price of oil slowed down the movement of oil because there was less incentive,” said Phil Flynn, an analyst with PRICE Futures Group. But even though Flynn says that producers are drilling less, he doesn’t think there will be any decrease in oil production this year.

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Yet the United States is still in the middle of an oil boom, even with the slowdown. Production in 2014 increased 16 percent, the largest increase by volume in U.S. history, according to the Energy Information Administration. As of February, domestic oil is being produced at a rate of over 9.2 million barrels per day, the highest ever, said the agency.

Much of that oil is being extracted via hydraulic fracking in the Bakken region of North Dakota, Montana and Manitoba, Canada. Since the first successful major fracking operation by Brigham Oil & Gas in 2009, production has expanded 10-fold.

From the Bakken region, the crude oil is either pumped through pipelines or, more and more often, loaded into tank cars and shipped via rail to either the Gulf Coast, the East Coast or the West Coast.

While the barrels of crude oil traversing the tracks of the nation has climbed steadily, the destination of the trains has shifted.

For four years, from 2010 to 2013 the overwhelming majority of the crude moved south, to the Gulf. Then a drastic shift in 2014 more than doubled the amount of oil moving to the East Coast.

Rail transports more than half of all the oil supplied to refineries on the East Coast for the first time in February of 2015 according to the U.S. Energy Information Administration. This represents an ongoing trend of the east coast favoring domestic oil over foreign imports.

“New York used to import their oil,” said Flynn. “Now they get their oil from the Bakken region,” one of the nation’s richest fracking fields centered in the Dakotas.

Flynn said that this flow of oil by rail from the middle of the country to the east coast is likely to remain steady for the next several years. He added that if the Keystone XL Pipeline is ever approved, it would result in another increase in the number of oil filled tank cars rambling across the country.

With six derailments of crude oil tank cars already this year, including one in Galena, Ill., an increase in traffic could have dramatic consequences.