In Connecticut, highways are an endangered species.

At least one highway is, anyway: the Merritt Parkway, a 38-mile-long stretch of winding roads and scenic views from Greenwich to Stratford.

The highway made the international nonprofit World Monuments Fund’s list of “irreplaceable” and endangered global treasures last week — in the company of the Biblical city of Lod in Israel and the Machu Picchu ruins of Peru. Supporters of the parkway feared that ongoing restorations by the state Department of Transportation intended to make the highway safe are destroying the highway’s unique charm.

Although the Connecticut Department of Transportation says it tries to preserve the Merritt’s rich landscape, ConnDOT officials and highway supporters have disagreed in recent years on how to improve the road and the surrounding forestry.

Built in the 1930s, the Parkway was intended for cars going a leisurely 35 mph, not today’s high speeds. More than simply a road to get drivers from one place to another, it provides a uniquely relaxing experience, said Jill Smyth, executive director of the Merritt Parkway Conservancy, the nonprofit that nominated the road for a slot on the World Monuments Fund list. She touted its gently rolling topography, quintessentially New England landscape and historic stone bridges.

To Herbert Newman, a critic at Yale School of Architecture, the Parkway is a national treasure — “the single most beautiful [man-made construction] in Connecticut, and maybe in the United States,” he said.

“It is to Connecticut what Yellowstone is to Wyoming and the Grand Canyon is to Colorado and Arizona,” said Newman, who has advised ConnDOT on the preservation of the Merritt since the early 1990s.

Though Merritt fans consider it living history, it was once a symbol of modernity. One of the first parkways ever built, it marked an important development in the evolution of the American landscape, said Erica Avrami, World Monuments Fund’s director of research and education.

“It’s emblematic of the role of the automobile,” she said. “The idea of ribbons of highway going through green fields connecting cities and suburbs is a truly American concept.”

The bridges across the Merritt — which were built in different architectural styles that include Art Deco, Neoclassical, and French Renaissance — earned the Merritt its place on the World Monuments Fund list, Avrami said. In many cases, it would be less expensive to build new bridges than to renovate the old ones, she said, but doing so would drastically change the appearance of the scenic parkway.

Most drivers on the Merritt aren’t aware that they are enjoying a priceless American treasure, but the list is intended to change that, Avrami said.

She said the World Monuments Fund created the list to attract attention to cultural landmarks and to bring to the fore discussions about conservation and the preservation of heritage.

ConnDOT spokesman Kevin Nursick said the department is committed to preserving the heritage of the Parkway, and knows it is more than just any old road. He said a committee comprised of highway stakeholders, architectural and landscaping experts and the Merritt Parkway Conservancy advise the department before it begins any work on the Parkway.

Even so, disagreements sometimes arise. In 2006, the Merritt Parkway Conservancy sued ConnDOT over a plan that would have drastically altered the highway’s aesthetic at its intersection with Route 7 in Norwalk, Conn.

Newman said he and other Merritt fans are currently at “loggerheads” with ConnDOT over a plan that is underway near Trumbull, Conn., which will restore 12 bridges, but also involves the removal of many trees.

Nursick said removing the trees makes the highway safer because some are placed where they could fall onto the road, or where drivers who swerved off the road might hit them. He said ConnDOT also wants to remove invasive plant species, which do not belong in the historic landscape. Nursick said the department wants to keep the highway beautiful — when construction is finished, workers will install roughly $2 million in new trees and plants in the now-barren Trumbull area.

“When it’s done, it’s going to look pristine, and it’s going to be historically accurate,” he said. “The Merritt is the queen of [Connecticut’s] highways, and we intend to keep it that way.”

Overall, ConnDOT has been willing to compromise with the highway’s devoted stewards, Newman said.

“This can be a win-win situation, not an adversarial issue,” he said. “But it takes constant vigilance and cheerleading. It’s not by major things that [the highway] could die, but little things, being chipped away.”