A controversial Massachusetts Avenue apartment and retail project appears poised to proceed thanks to the addition of an underground garage meant to allay neighbors’ concerns about parking.

The developers of Trail Side on Mass Ave, a $10 million project at 875 Massachusetts Ave., had expected to win approval for the project at a meeting of the Indianapolis Historic Preservation Commission April 7. Instead, the commission sent the developers back to the drawing board come up with a new parking plan.

Newly revised plans for the project will be heard by IHPC on May 5. Approval would allow Riley Area Development Corp. and its partner in the project, Monument Realty, to proceed with the four-story building, which would replace a vacant, one-story structure owned by the Center Township Trustee.

Trail Side is to include 69 one-bedroom apartments and 10,900 square feet of first floor retail space. The developer had proposed 23,000 square feet of retail space, but the amount was reduced to accommodate office space and community meeting space that was to have been provided in the building’s basement. The basement of the building will instead house a 69-space parking garage, satisfying the demands of a property owner and retailers across the street who wanted the project to include more parking. A surface lot behind the building will accommodate 25 more spaces.

Tom Battista, whose commercial building across the street houses the popular R Bistro restaurant and other retailers, had led opposition to the Trail Side project. He cited inadequate parking as a threat to the economic interests of his tenants.

The change in the Trail Side plan “diminishes our concerns a lot,” said Battista, who hadn’t yet heard complete details of the revised plan but was aware of the parking change. Battista praised the addition of parking and the retention of retail space on the first floor. “They are going to do the right thing now.”

Bill Gray, Riley Area’s executive director, said it’s likely his group will move its offices to Trail Side from the Davlan, a building in the 400 block of Massachusetts Avenue. Riley Area and Monument Realty previously redeveloped that building with a mix of apartments and retail space.

Gray said Riley Area has agreed to a long-term land lease with the Center Township Trustee’s office, which owns the project site. He said final details of that lease are being negotiated but aren’t expected to delay the project.

IHPC already has approved the demolition of the building that must be removed to make way for Trail Side. If IHPC approves the project design on May 5, Riley Area will likely close in July on the sale of the tax credits being used to finance the project.

Demolition of the existing building would take place in September or October with construction following shortly thereafter, Gray said. He anticipates being able to lease apartments and retail space beginning in fall of 2011.

Trail Side apartments are to rent for between $325 and $700 a month to tenants with incomes between 30 percent and 60 percent of the median income.

Trail Side is so named because of the Indianapolis Cultural Trail, the northeast segment of which will run along the front of the building. Construction of that leg of the trail is in progress.

The Trail Side architect, the local firm A2SO4, is working with R.W. Armstrong, the engineering firm in charge of the Cultural Trail, to coordinate construction schedules so that neither project causes delays for the other.