Strange sight in Arizona: Why are almost 300 Union Pacific trains lined up for 3 miles?

It's a fascinating sight: about three miles long, snaking through the Arizona desert. If you've ever driven on Interstate 10, southeast of Tucson near Benson, you can't miss it. More than 300 Union Pacific locomotives lined up on a siding, just waiting for a train to pull.

Union Pacific Railroad is in the freight hauling business. You can see their trains all over Arizona, mostly pulling freight from the west coast back into the interior of the country. In fact, these yellow engines are a common sight if you are driving anywhere along I-10.

"For the last 155 years, we've been carrying freight across the western half of the United States to the borders north and south," said Jeff DeGraff, Director of Media Relations for Union Pacific.

Union Pacific operates about 8,500 locomotives, over 31,000 miles of track in 23 states, but why aren't these engines pulling anything?

"It is a strategic reserve of locomotives for Union Pacific," said DeGraff.

We talked to DeGraff by Skype in Texas about this strange sight in southern Arizona. Union Pacific diesel locomotives, lined up end to end for about three miles.

"Right now, we have just under 300 locomotives we have stored out there," he said.

We took a look with our SkyFOX drone and sure enough, there are at least 300 engines parked on this siding. Some are in better shape than others. We're not sure where one got all the graffiti, but like airlines who store extra planes in Arizona, Union Pacific knows our climate is ideal.

"Finding a good, open space with arid, dry climate there that's good for the machines, we don't have to worry about too much rust and rain and things like that, so it's a good spot for us. We were fortunate to use that piece of track that we could use," explained DeGraff.

Thanks in part to a downturn in manufacturing, not all of the locomotives used by Union Pacific are needed all the time.

"Over the last several years, you've seen some downturn in manufacturing and other aspects of the economy. Union Pacific has felt that as well," said DeGraff.

So the railroad has several spots for storing these locomotives. This area near Benson, Arizona has the most.

These engines are checked and maintained on a regular schedule. After all, at $1 million to $3 million a piece, they are something Union Pacific keeps an eye on.

"We make sure that when we do need to pull them back into service, that they are ready to go," said DeGraff. And while they are an interesting sight for drivers using I-10, "..we ask drivers to keep their eyes on the road."

These trains are not a tourist attraction.

"We encourage the public to appreciate the beauty of them, but do it from a safe distance," DeGraff added.

Union Pacific moves its stored locomotives in and out of its facility near Benson all the time, so again, please don't ever get too close to the tracks.