NEW YORK (TheStreet) -- To people outside the Northeast, stories about Amtrak seem quaint.
Stories about people huddled overnight in trains or of entire train systems going down due to extreme cold are oddities to most Americans because passenger train systems themselves are a product of something most of the country doesn't have.
As population density increases, the need for transit grows because trains scale better than cars. Places like Manhattan could not exist if everyone had to drive a car to get anywhere. The roads are jammed as it is.
As population density increases, the cost of road travel increases exponentially. Roads have to be repaired more often and accidents happen. Roads under repair create traffic jams, and frayed nerves create more accidents.
With trains you can add cars and increase trip frequency. Density makes the train experience more convenient and comfortable.
I learned this on a recent trip to New York City. I was able to get from Times Square to downtown at 11:30 p.m. without even thinking about the schedule. During the same hours in Atlanta, which is less dense, trains run 20 minutes apart.
So in our biggest cities, and in traveling between cities close to one another, passenger trains remain essential. For other parts of the country, not so much.
This is reflected in Amtrak's finances, which illustrate the irony involved in the whole "train subsidy" debate.
Amtrak loses $1.5 billion each year, but dropping routes that are more than 400 miles long would let it break even, according to a Brookings Institution report from last March.
In other words, it's in serving the people who oppose train subsidies that the need for subsidies is created.
Since 1997, the Brookings report adds, Amtrak traffic has grown twice as fast as air passenger traffic. As the country becomes more dense, the economics of train travel become more attractive.
Trains are big, so when they have problems they make headlines. It was big news yesterday when service was cut between Philadelphia and Baltimore, and bridges in New England were closed. But freeway travel was little better during those hours, and air travelers were still waiting for weekend flights out as this was written.
Beyond major transit corridors, the economics of trains change. Density doesn't define profitability. Efficiency defines it. Freight can pay its own way because trains are far more energy-efficient than trucks, and the delays in moving cars through intermodal stations matter less when it's not you but your stuff that is sitting on a siding.
So no one thinks of subsidizing such freight companies as CSX (CSX) or Norfolk Southern (NSC). Both companies whose rails pass by my home, are profitable. But my transit system, called MARTA, does require regular subsidies, because Atlanta lacks the density to make it valuable outside the urban core.
The two different economics of train service -- density and efficiency -- define the political debate about trains that has divided the Northeast from the rest of the country for a generation. But they come down to the same economic fact: Trains scale. In all kinds of weather.
At the time of publication the author had no investments in companies mentioned in this article.Follow @danablankenhorn
This article represents the opinion of a contributor and not necessarily that of TheStreet or its editorial staff.