In transportation, as in everything else, knowledge is power.

Centuries ago, greedy European kings jealously guarded the maps to distant lands that were developed by their explorers. Today, many commuters shroud their work routes in secrecy for fear of encountering more competition for lane space.

But there’s a portion who are willing to be generous with their travel tips.

This letter came in response to a January column in which Kate French of Vienna sought guidance on commuting from there to Crystal City. French wrote that Interstate 495 is “almost always great. It’s the rest of the drive that is torture. Metro takes way too long and is expensive.”

A 30-second exposure of traffic (at right, southbound cars’ white headlights) flowing across the 14th Street bridge into and out of the District, as seen from Crystal City. (2000 photo by Frank Johnston/THE WASHINGTON POST)

Dear Dr. Gridlock:

I made this run, between Vienna and the northernmost section of Crystal City, for several years. The most reliable route in terms of average speed, bailout options and general stress was as follows:

→Gallows Road to Lee Highway (Route 29).

→Exit Lee Highway to Hillwood Avenue in Falls Church.

→Hillwood to Arlington Boulevard (Route 50) via the Seven Corners intersection. That intersection is challenging, and the traffic signal cycles are long, but it was predictable.

→Exit Route 50 onto South Washington Boulevard, go past Fort Myer and under Interstate 395.

→Connect to Army-Navy Drive in Crystal City.

One variant on the return to Vienna: The Seven Corners exit to Hillwood Avenue entails an egregiously long traffic signal, so I would exit Route 50 a little farther west and snake through a neighborhood to get to Hillwood. (Remaining on Route 50 westbound beyond this point would be a crawl, because it narrows to two lanes at Seven Corners.)

Earl Boyanton, Vienna

DG: The next letter-writer, a professional engineer, is a frequent correspondent. He also saw French’s comments and made some points about the costs of driving vs. transit.

Dear Dr. Gridlock:

You quoted Kate French of Vienna about her slow and costly Metrorail ride to Crystal City as compared with her pleasant trips on I-495. She might honestly feel that way, but it is illogical.

There are 13 miles between Vienna and Crystal City, for a peak round-trip Metro fare of $10.50, which is about 40 cents per passenger-mile. AAA figures it costs $8,500 per year to own and operate a mid-size car, which is typically 63 cents per passenger-mile for a single occupant. Because French might own the car for trips other than commuting, she can deduct 16.5 cents per mile for ownership costs that she cannot save by riding Metrorail.

On the other hand, the insurance cost goes up for auto commuters over a 26-mile weekday round trip. Considering that, it is safe to say Metrorail at peak fare is 6.5 cents per mile less than the incremental auto cost. Metrorail will save her $424 per year compared with driving on I-495.

In part, I fault Metro for not advertising its low-cost travel. True, fares are higher here than most places, but that is because our local governments will not pay a fair share, as those in most other metropolitan areas do. Many have a sales tax just for transit. Portland, Ore., has a tax on employees, because most of them commute somehow.

When I was transit commissioner for Youngstown, Ohio, long ago, I had to make the schedules and fares, which by law had to provide a 6 percent return on the transit investment. If not, by law, I had to raise the fare. The bus system lost riders every year, so I had to raise fares to cover the loss of revenue.

At one point, the transit system ran newspaper ads promoting the big annual savings of commuting by transit. Bus riding increased while these ads ran, the only time ridership quit falling.

Ed Tennyson, Vienna

DG: I’m familiar with both sides of the cost argument, because I hear about it from readers whenever we test a driving commute vs. a Metrorail commute. They will want to add in layers of cost, such as the driver’s cost to park in the middle of the District and the Metro rider’s cost to park at an outer station. Others will note that both roads and rails are subsidized by taxpayers, adding another layer of cost.

The economics are complicated enough, but they don’t account for other factors, such as stress, that commuters also learn to take into account.