One of the truisms of U.S. transportation planning has long been that each year, there will be more cars on the road.

This has been the case for decades. But not the past decade. Even before the economic recession put millions of people out of work or the recent spike in gasoline prices, the growth in the amount of driving per capita (also known as vehicle miles traveled) had peaked and is now in decline.

And it’s a trend that is being led almost entirely by young people. As a newly released report documents, the average 16-to-34-year-old American is driving 23 percent fewer miles than the average young person drove in 2001. Yet, over that same period, the number of miles traveled on public transit by people of the same age range has increased 40 percent.

Today’s young people are far more inclined to walk and travel by bike as well, up 16 and 24 percent, respectively, according to the report. They even are deciding not to get a driver’s license (26 percent of 16-to-34-year-olds don’t have one compared to 21 percent a decade ago).

There are any number of reasons for this. Obviously, a desire to economize is one. But the trend clearly transcends mere cost. According to a National Association of Realtors study, the younger generation prefers to live closer to shopping, schools, public transit and other conveniences than their older peers. They also want to have less adverse impact on the environment.

Yet this big shift in attitudes seems to be getting lost on many in Congress and on their counterparts in state capitals where the preference for spending tax dollars on highway construction rather than sidewalks, bike lanes and public transit remains high.

House Republicans have frequently targeted funding for Amtrak and President Barack Obama’s high-speed rail program for elimination as well. They’ve also expressed interest in wiping out all mass transit funding from the federal Highway Trust Fund.

Democrats have generally rallied in defense of public transit spending in Congress.

The danger is that transportation policy will continue to be shaped by elected officials who only look backward and repeat the mistakes of the past. As gasoline prices continue to rise — and most analysts believe they will — it will no longer be just young people who demand transportation alternatives, but older Americans as well.