In the above examples, driving yourself came in cheapest for the Los Angeles to Las Vegas experiment. The bus was best for the Boston to New York and Indianapolis to Chicago trips. Additionally, note that if more people are joining you, a self-drive trip might work out to be more economical than the other options, as you'll have several people to split the cost of fuel. But with each of these, you'll be spending significantly more time in transit.
Beyond the test data, here are other items to consider:
For air travel, factor in fees for baggage and other services, time spent at the airport, possible weather delays, and the cost of transportation to and from the airport.
For road trips with your own car, you'll want to consider traffic, toll costs, and general wear-and-tear on your vehicle.
In every case, you'll want to take your personal comfort into account. Are you a traveler who hates coach-class seating? If so, you'll probably prefer train travel or taking your own car. Can you not stand sitting in traffic? Skip buses and driving and instead hop on a plane or train.
Then there are more minor, but still important, factors.
Driving your own car allows you to blast your music, make fuel and food stops at your own discretion, and change plans en route in response to traffic, weather conditions, or other factors.
Taking a bus, train, or plane gives you less freedom, but more down time during the actual traveling -- no stressful behind-the-wheel situations here. For the most part, you can pop on your MP3 player, grab a snack, and (hopefully) enjoy the trip.
For these differing types of travel (and their related costs), choosing your method of transport is truly a value judgment.
As noted earlier, how you interpret the data is going to be different for every traveler.
Let's use me as an example. Years ago, as a college student, I would have gone with the bus for most short-haul travel -- it's cheap, safe, and the travel time isn't too restrictive for a weekend getaway. Nowadays, while I still take the bus from time to time, I might spring for the train or a plane if I want a little more comfort while traveling, or more time at my destination.
Conversely, a family of five might find a road trip much more affordable (and manageable) than corralling kids on a plane. And a business traveler, who's just spending a few hours in her destination, may exclusively fly to make the most of her time.
If you're planning a short-haul trip this summer and have several transportation options to choose from, conduct your own experiments to see which provides the best value to you.
Sarah Pascarella is a Senior Editor for Smarter Travel and writes the Sarah's Travel Tips column. She shares the best advice for travelers on issues including booking, planning, comfort, safety, and convenience. SmarterTravel provides expert, unbiased information on timely travel deals, the best value destinations, and money-saving travel tips.