Finding out how much it will cost to take the train between any two locations is simple. Just go to the Amtrak Web site and ask. On their trip planner, plug in the station you plan to leave from, the station you want to arrive at and the date when you want to travel. Click "Go!" and you'll be shown the range of fares for your trip. At this writing, fare for one adult from Union Station in Washington, DC, to Penn Station in New York, NY, on Sept. 17, 2011, is $49 for one adult on the regular train, $139 on the Acela express.
Of course, the fare won't be the only expense associated with your train trip. Since you aren't taking your car, you may need transportation once you arrive at your destination, so you might have to factor in the cost of a rental car or using public transportation Check with the rental car agency of your choice to find out the cost of a car rental for your entire stay.
Calculating how much it will cost you to make the trip by car is a bit more complicated. Some recent model automobiles can calculate your mileage for you and even predict how far you'll be able to drive on your current tank of gas. If you don't have a car that's quite so intelligent, you'll need to calculate the mileage yourself. You probably know the drill: Wait until your tank is close to empty, fill it up, note the number of gallons you bought and see how many miles you add to your odometer by the time your tank is almost empty again. Finally, divide the number of miles you've added to your odometer by the number of gallons you bought and you'll have a rough estimate of your miles per gallon (mpg).
Now go to Google Maps or a similar service and find the miles that you'd have to drive to get to your destination. For a trip from Washington, DC, to New York, NY, this is roughly 240 miles (386.2 kilometers). Divide this by the mpg you calculated above and multiply it by the current cost of a gallon of gas. That's the gas cost for your trip. To keep things simple, we'll assume that your car gets an average of 30 miles to the gallon (12.75 kilometers per liter), and that the gas you use currently costs $4 a gallon. Divide 240 by 30 and you get 8. Multiply 8 by $4 and you get $32 for the total gas cost. Even for one adult, that's cheaper than the train fare between those two cities, so it looks like the car wins out on gas price, at least in that example. Your results may vary. But bear in mind that, depending on your destination, you may have to pay for a place to park your car once you're there. (This is especially true in large cities like New York.) By the time you've made the round trip, you'll probably be ready for an oil change and there may be additional wear and tear expenses on the car. And for longer car trips you'll need to pay to spend the night in a motel along the way. This can actually make the car trip more expensive than the train trip.
Of course, we've been assuming that this is a trip for one. The moment you start adding additional passengers, the train trip becomes substantially more expensive but the car trip doesn't. If price is the deciding factor, the car trip will usually be the cheaper one for anything more than a single passenger or a single passenger with infant child in tow. (Kids under two generally ride the train free.) In the end, though, your choice of train or car may come down less to price than to whether you're in the mood to drive or would rather kick back for a few hours and read a good book.