Fast is relative. Sometimes I take either the Amtrak regional train or a bus from New York City to Philadelphia. When I do, I whine nonstop about how long it takes -- generally an hour and a half on the train, two hours by bus. If I were in France, I always say to myself, I could be there in 45 minutes on a high-speed TGV train.

But if I were living in 1800, it would have taken me two days traveling by stagecoach. I learned this recently in reading an abridged edition of Henry Adams’ History of the United States of America During the Administrations of Thomas Jefferson and James Madison, first published in 1889. It set me off thinking about the nature of fast and slow.

Adams was making the point that life changed dramatically in this country in those 17 short years between the start of Jefferson’s presidency and the end of Madison’s. In 1800, “even the lightly equipped traveler found a short journey no slight effort,” Adams wrote. “In the Northern states, four miles an hour was the average speed for any coach between Baltimore and Bangor.” That meant Boston was a four-day journey from New York. A trip to Nashville took three weeks.

By 1817, it took only a tad more than a day to travel from the Big Apple to the City of Brotherly Love. In those days, that qualified as superfast. Just as now, cities, states and nations were constantly trying to enable people and products to get to places faster, and each jump was revolutionary at the time.

Adams, who lived from 1838 to 1918, was an eyewitness to the most dramatic changes. As an adult he experienced both the Civil War and World War I, and saw America go from a society of wagons and horses to one of planes, trains and automobiles.

I’m usually a big fan of progress. But reading Adams, I was prompted to think about how relative it all is. Today’s fast is tomorrow’s slow. Which to me, when I’m in a reflective mood, makes transportation improvements seem pointless. Why labor so hard to build a TGV-style line along the Northeast Corridor if it will seem as slow as molasses in a generation? And speaking of high-speed trains, shouldn’t a more accurate title be chosen? TGV stands for train à grande vitesse -- “train of great speed.” But great speed today is not great speed tomorrow.

This principle is on display in Japan and other points to the east. The Central Japan Railway Company is actively at work on a line between Tokyo and Nagoya that will go more than 300 mph. The existing Shinkansen “bullet train” travels at between 150 and nearly 200 mph, but is old now -- it opened in 1964. Railway officials think there’s a market for a train that travels the 220 miles to Nagoya in 40 minutes.

The Japanese are doing this in part to keep up with the Chinese. In addition to constructing the world’s largest network of high-speed trains, the Chinese are also reportedly researching a super maglev train that would travel inside a vacuum tube at something like 1,850 mph. So my journey to Philly might one day take … four minutes?

Now let’s look at the United States. Amtrak’s fastest trains aren’t much faster on average than the best trains of the 1920s. And with the loss of the supersonic Concorde, the top end of passenger air travel is slower than it used to be as well.

Then there’s outer space. Virgin Galactic, Sir Richard Branson’s commercial space company, says it’s studying passenger service that would carry travelers from London to Australia in two and a half hours. The prison transport ships that made the same voyage in the 18th and 19th centuries took nine months.

In the Star Trek TV shows and movies, the characters use the ship’s teleporter to instantly beam to the surface of a planet and back again. If such a thing existed in real life, the idea of place as we know it might disappear. That’s not a rosy scenario: If anyone could go anywhere at once, then wouldn’t the distinct agglomerations of places like New York City gradually dissolve?

That’s already happened in communications. Because of the Internet and the cellphone, we can now access both one another and almost any piece of information instantly, often at no appreciable cost. That’s cool, but something is disappearing.

So when is fast fast enough? When we enjoy the ride, I would say. As Confucius put it, “Roads were made for journeys, not destinations.”

Tell that to a transportation planner. But seriously, what helps us enjoy a ride is not only a clean train compartment and good conversation. It is the experience of traveling from one place to another. This is something that we should consider when we make transportation improvements.

Consider the interstate highways. If steps had been taken to limit the number of off-ramps, they would have become what they were originally envisioned as -- high-speed travel corridors between distant cities. But with ramps every few miles, the interstates, like I-35 that stretches from Laredo, Texas, up to Minneapolis, have become long, linear cities with a near-constant movie screen of roadside homes and businesses.

I’d like to say more, but I’m hungry. I’m going to take a walk to a lunch spot I like. It will only take me about 10 minutes, or, say, the travel time in a hundred years from New York to Philly.