St. Louis ? A St. Louis-based group says turning Interstate 70 near the Gateway Arch into a tree-lined boulevard could generate the potential for more than $1 billion in development near the iconic landmark.

The St. Louis Post-Dispatch reported Monday that the group “City to River” believes removing the interstate from downtown would make room for new buildings, create an area more attractive to the travel industry, and give new life to stalled developments like the Bottle District.

Big changes could be in store for the area around the Arch. An international competition is under way to redesign the 91-acre Arch grounds by its 50th anniversary in 2015. Also, a new Mississippi River bridge is scheduled to open by 2014.

City to River includes a volunteer group of architects and urbanists. The $1.1 billion estimated development potential is over a 20-year period. It helps give some idea of the possibilities for St. Louis if I-70 is removed from downtown, said Alex Ihnen, one of City to River’s organizers.

For years, civic leaders, including former Republican Sen. John Danforth, have sought to find a way to connect downtown with the Arch grounds and the river. Right now, the interstate makes it difficult to move freely from downtown. Bridges cross above the interstate, but traffic is heavy and walking can be dangerous.

The National Park Service, which operates the Arch and its grounds, launched the international competition to redesign the grounds.

The City to River’s project would stretch 1.4 miles and replace the interstate with a tree-lined boulevard that would feed into I-70 by the new bridge.

The project would essentially shift Memorial Drive to the east, creating an additional 3.2 acres of prime downtown real estate, with more land to the north.

It was 45 years ago that the interstate cut downtown off from the river.

“A disastrous decision,” said Jeff Rainford, chief of staff to Mayor Francis Slay. “What do you do about it?” he asked. “That’s another question.”

Ultimately, the Missouri Department of Transportation would have to approve any decision to dig up I-70 through downtown. MoDOT spokesman Drew Gates said the agency is open to the City to River idea.

But the stretch of roadway carries heavy volume — 50,000 vehicles per day. MoDOT officials aren’t sure if replacing it with a narrower boulevard, with stoplights and pedestrians, is workable.