Traffic impacts were a chief concern as informal public discussion around expansion plans for the Vineyard Haven Stop & Shop began before the town selectmen Tuesday night.

The project, which would double the size of the existing grocery store on Water street, will be formally reviewed by the Martha’s Vineyard Commission as a development of regional impact beginning next month. Stop & Shop spokesmen have been meeting with the commission land use planning subcommittee for a number of weeks. The first public hearing before the commission will be held June 6.

Under the proposed plan, a two-story building would be constructed, with the main store on the second level and a 43-space garage beneath. The garage is also a solution to flooding concerns, lifting the store space out of the low-lying flood plain.

In addition to creating new parking spaces, Stop & Shop hopes to work with the town to reorganize the municipal parking lot adjacent to the store.

Traffic in the Water street and Five Corners area was a central topic for discussion.

“I am somewhat concerned with the number of parking spaces,” selectman Tristan Israel said. “On the one hand, more parking is great [but] we’re bringing more cars to the heart of town when it’s really busy. It’s a two-edged sword.” Mr. Israel suggested that Stop & Shop could help alleviate high traffic by working with Tisbury on the Park and Ride system, and designate employee-only spaces within the garage to free up space in the municipal lo t.

Stop & Shop has already eliminated a proposed garage exit onto Water street from the plans after the Tisbury planning board expressed concern about traffic backups at Five Corners.

A traffic study conducted by Vanasse Hangen Brustlin of Boston was found to be incomplete, commission executive director Mark London said, due to the modeling system used to predict future traffic flow being incompatible with the unconventional layout of Five Corners. The commission recommended gathering new count data during Memorial Day weekend to better predict peak traffic.

Tony Peaks, chairman of the planning board, said he had also spoken with the commission about possibly reversing the direction of Union street, which is currently one way and exits onto Water street.

“The first step is to run the traffic model and get some sense . . . of the impact on Five Corners,” Mr. London said. “I think people in their gut feel . . . how big a deal [traffic] is going to be.”

Mr. Peaks said he hoped to see a rendering of the building in the context of the Water street area, as current renderings show the store in isolation. This step is a requirement of the commission process, and will be completed within two weeks, said Geoghan Coogan, an attorney who represents Stop & Shop.

Another change from the original proposal concerned a 19th-century home at 15 Cromwell Lane. The house was purchased by Stop & Shop last year as part of the expansion plan. Initially, the house was to be demolished, but a historical analysis showed that it was one of a handful of Tisbury buildings predating an 1883 fire that destroyed much of Main street. Last week, the Massachusetts Historical Commission determined the home was eligible for listing in the National Register of Historic Places.

“When we first made the application, we had no idea the house was as old as it was,” Mr. Coogan said. “Our intention [now] is not to demolish it; we’d like to move it.”

In addition to moving the house, Mr. Coogan said plans are in the works to preserve the large mural on the side of the current building.

“That mural is going to stay on the building somewhere,” he said.

Ned Orleans, a former longtime member of the planning board and the town’s appointed member of the commission, said it is important to view the proposal as more than just a Stop & Shop plan. The project will affect the entire downtown area, he said.

“This is not a small deal,” Mr. Orleans said. “It’s not just a matter of almost double the size and square footage and then walking away from it . . . we’ve had the same problems for a long time in the existing conditions, and all we’re going to do is make them worse unless we find some other way [to help].”

Mr. Orleans and Mr. Coogan encouraged people to attend the public hearing on June 6.

“Take advantage of the available information and prepare statements, and you will be able to participate in all of these meetings . . . it’s an open process,” Mr. Orleans said.