A COUPLE OF TIMES a month, usually after church and with dinner in mind, Wilbur Simonson, 88, and his wife Norma, 85, will drive to Mount Vernon on the Mount Vernon Memorial Highway.

On this highway -- the original stretch of the George Washington Parkway, south of Memorial Bridge -- the Simonsons rarely make it all the way up to the 40-mph speed limit. This is partly because they're not in a hurry, partly because Norma Simonson doesn't like her husband to drive too fast, and partly because Wilbur Simonson never tires of enjoying -- or checking up on -- his work. It's just outside the power windows of his 1980 Olds Cutlass.

It is the Mount Vernon Memorial Highway. Simonson helped design it.

That was about 55 years ago. About 20 years ago, the career landscape architect and highway consultant retired, but he and his wife still livheir longtime Bethesda home, and Simonson himself is still proud of the pioneering project. And he still takes great pleasure in personalizing these 15 curving, carefully landscaped waterside miles of highway. But then, personalizing a functional highway was the original point.

"This is the beginning of what has been my life's work, and my dream," he says, driving a visitor on a meticulous, meandering tour one recent morning. "And the thing I'm thankful for is that I've lived long enough to see it appreciated."

The project took three construction seasons and cost $7.2 million -- a then unheard-of $500,000 per mile -- and opened on January 16, 1932, a date Simonson doesn't have to pause to remember. "That's three days before our anniversary," he says, exchanging a smile with Norma (they've been married 67 years). "And it was formally dedicated on November 15, 1932. That's her birthday." He leans forward, grinning. "That's what I call the aesthetic side of engineering, the personal side. The highway was meant to mean something to people, its vistas designed to facilitate something called 'making pictures as you drive.'

"And that's why we've come here, every month or so, all these intervening years," he says.

In 1928, Simonson and others at the Westchester County Parks Commission who had worked on the Bronx River Parkway -- the country's first "scenic" highway -- were recruited by the federal Bureau of Public Roads, then part of the Agriculture Department, to design and build a commemorative highway from the soon-to-be-completed Memorial Bridge down to George Washington's Virginia estate.

The overriding principle, Simonson says, was to devote as much thinking to the road itself -- which incorporated the first federal-highway cloverleaf (at the 14th Street bridge) and divided-lane construction -- as to what people would remember, having driven it.

"You don't remember the road," he says. "You remember the living part, the biological side, the nature and the terrain. I call the principle we worked under 'bio-engineering.'"

Simonson, Park Service engineers and others looked at several routes -- including the one now roughly followed through Alexandria by Shirley Highway -- and decided that the river route, though it would involve many bridges and few straight lines, would best allow them to meet the challenge of "continuing that park-like, beautiful character of Washington, D.C. along the river, all the way to the home of the first president," Simonson says.

"It was curvilinear, the basis of modern highway design, fitting itself to the lay of the terrain," he says, as we enter the long bend just before the highway ends in a wide grassy oval at Mount Vernon. "Used to be that lots of engineers would be proudest of the longest straightaway they could build. Of the 15 miles here, there are about three that are straight. It's graded in such a way that you could drive this curve in the Big Six, which is what we used to call the Pontiac, and let go of the wheel -- and at the 35 mph design speed limit, the car would follow the road right around by itself."

The river route also made for the most appropriate recreational possibilities, Simonson says, as he stops the car among the laurel and dogwood at the end of one of the Mount Vernon estate's two scrupulously hidden public parking lots. There's a sign here marking the start of the Mount Vernon Bike Trail.

"When we designed the road, in the '20s," he says, "we envisioned this as a future bridle trail. George Washington used to take this route from his estate up to Alexandria, to pick up mail and whatever, stop for a glass of beer or wine at the Old Club on the way back. It was about 15 miles either way -- a day's work for a horse. And now it's a biking and jogging trail, thanks to the Park Service, and that's just as appropriate.

"But I just wanted to show you," he says, pulling away slowly, "the kind of thinking that went into this project."