Washington ? America is getting cleaner, litter experts say.

They estimate that deliberate trash-tossing has fallen about 2 percent a year since the mid-’70s in communities where it’s been measured.

On U.S. beaches, cigarette butts, beverage cans and Styrofoam peanuts for packaging are down, cleaners say. In most communities, pooper-scooper laws now make carefree strolls possible. Even along roadsides, more of what’s visible today is grass.

Remarkably, the improvements come despite an increase of 90 million in the U.S. population since widespread trash surveying began in 1974.

If you haven’t picked up on litter’s decline, don’t be surprised. People raise their standards as places get cleaner, so they’re never impressed, according to John Doherty, New York City’s sanitation commissioner. “The more you improve the cleanliness level, the higher people’s expectations are.”

Doherty, 69, who started out as a city street-sweeper in 1960, has lived the progress.

Thirty years ago, independent assessors rated nearly half of New York’s streets and sidewalks as filthy. “A sweeper’d go out and there’d be mounds of steaming dog waste,” Doherty said. “That was tolerated then.”

Twenty years ago, New York was still so dirty that humorist Dave Barry accused the mayor of having appointed a Commissioner for Making Sure the Sidewalks Are Always Blocked by Steaming Fetid Mounds of Garbage the Size of Appalachian Foothills.

Today, the same independent assessment system used 30 years ago rates 95 percent of New York’s streets and sidewalks as clean. Once-rare litter penalties now are the second biggest source of the city’s revenue from fines, after parking violations.

As New York goes, so goes the nation, albeit by fits and starts, since litter curbs are almost entirely a local or state matter. For example, in Washington state, a multimedia “Litter and it will hurt” campaign warns motorists of the state’s serious litter fines: $1,025 for tossing a lighted cigarette, for example. The effort has cut litter by 20 percent on state-overseen highways and roads since it began in 2002, according to Megan Warfield, the state’s coordinator of litter programs.

Beyond enforcement, many factors aligned against litter. Recycling, for example, has made people more conscious of solid waste of all kinds. Tourist destinations discovered that it paid to be litter free. The same schoolchildren who pulled cigarettes out of their parents’ mouths got on them when they littered.

It isn’t that U.S. attitudes toward litter changed, said P. Wesley Schultz, a social psychologist at California State University at San Marcos.

“People now feel littering is inappropriate and that others will disapprove of them if they litter. The norm about what’s right and wrong changed.”