One of the reasons the train vacation works is the availability in these cities of mass transit.

Most major attractions in Boston, New York and Washington are served by subway systems or other forms of public transportation.

Finding discount tickets is not difficult in any of these cities.

In Boston, we purchased four passes good for three days of riding MBTA for $18 USD/each, a total of $72 for transportation limited only by hours of operation and our desire to cover the city.

A single-day pass is $7.50.

In New York, the MetroCard One Day Fun Pass is $7 (no three-day option here, but the seven-day pass is $24). Once again, our total is $72 for three days and four people. On the fourth day, we purchased traditional one-way tickets from hotel to Penn Station at $2 per person. Total for New York: $80.

In Washington, the One Day Pass is $7.80 per person and allows unlimited Metrorail travel. Beware: On non-holiday weekdays, it isn't valid until after 9:30 a.m. Those wanting an early start on the lines will have to buy a single trip ticket starting at $1.35.

Four days with the One Day Pass for four people came to $104.

Total costs for riding the three systems: $256. All of these charges were paid by credit card in vending machines.

So riding mass transit trains and Amtrak for 10 days in a very expensive part of the United States came to just more than $600 for four people.

That's about $15 a day per person for getting around three great cities without buying a drop of gas or paying a single parking fee.

More information: Money saving transportation tips.