ARLINGTON, Va. -- Meandering through wooded hills, the George Washington Memorial Parkway offers stunning views of the Potomac River and the capital's monuments beyond. It also offers one of the most direct commutes to downtown Washington for suburban residents -- and that has brought traffic it was never intended to handle.

Unlike an ordinary highway, the GW, as it's commonly known, can't just be widened, flattened and straightened to make room for more vehicles at higher speeds. The road is the property of the National Park Service, and its central mission is to showcase the area's historic sights and natural beauty.

Around the country, old parkways designed with aesthetics in mind are bumping up against modern realities, turning scenic roads into hotbeds of commuter frustration.

Classic parkways are ill-suited for heavy traffic because they often contain sharp curves and steep hills and lack features like merge lanes. The challenge for the agencies overseeing them is to balance historic and scenic value with the need for safe and free-flowing arteries.

"It's a real balancing act. It always has been, and it becomes more so as traffic increases," said Jon G. James, acting superintendent of the GW.

The road runs 25 miles in northern Virginia from the Capital Beltway to George Washington's Mount Vernon estate, with two lanes in each direction. The smaller Clara Barton Parkway in Maryland across the Potomac is also part of the GW.

Park officials estimate that 75,000 to 80,000 vehicles drive on the parkway every day -- far more than intended.

The GW is not alone in its beauty or its challenges.

On the West Coast, the Arroyo Seco Parkway follows a dry riverbed from Los Angeles to Pasadena. With large bands of parkland running parallel to it and several historic monuments located off it, the parkway is considered California's first freeway.

But critics say it has been poorly adapted to handle today's traffic, contributing to frequent accidents.

Despite their practical flaws, parkways are important to preserve and can even provide a model for future construction, advocates say.

"The experience of driving doesn't have to be terrible. There's still room for beauty and enjoyment," said Kevin Fry, president of Scenic America, a not-for-profit dedicated to preserving the nation's "visual character." Fry's group advocates flexibility in road construction and upgrades. Such compromises can be used to improve safety features of parkways while still maintaining their aesthetics.

On the GW parkway, guard rails, which were not part of the original design, have been added. But rather than using metal fixtures, the park service used steel-backed timber to give them "a more rustic, historic appeal," James said.