SCARBOROUGH — The Planning Board last week unanimously approved a concept for potential phase 2 development of The Downs.

The 150-acre parcel is on the northern portion of the property and has been dubbed the “Innovation District” – designated for a mix of light industrial, manufacturing, research and technology uses, as well as general commercial and retail development.

Infrastructure work for the residential portion of the development, which is phase 1 of the project, is already underway and is expected to be completed next year.

Planning project manager Dan Bacon, of Gorrill Palmer Consulting Engineers, spoke Tuesday night on behalf of Crossroads Holdings LLC, the partnership that includes developers Rocco, William and Marc Risbara of Risbara Bros. Construction Co. and Peter and Richard Michaud, who purchased the 510-ace property in January for $6.7 million. Rocco Risbara was also present at the Dec. 18 meeting to answer questions about the conceptual master plan.

The developers plan to turn the property, which has been the site of the Scarborough Downs harness racing track since 1950, into a mixed-use downtown under a 30-year tax-increment financing package worth up to $81 million.

Under the conceptual master plan, Bacon said the Innovation District will have two distinct areas with different design goals and “characters.”

Three large lots, planned at the corner of Payne and Downs roads with frontage and visibility from both streets, is thought to be best suited for commercial development, with a planned retail component.

The second and primary area, which consists of the remaining 52 lots, is envisioned as a light industrial and manufacturing area.

Because development will be market-driven, Bacon said the district’s lot sizes are deliberately designed to be “flexible and combinable” to accommodate a range of building sizes and uses.

Board member Rachel Hendrickson said it “troubles” her not knowing what could be built in the large front commercial lot.

“I’m concerned about ‘terra incognita,’ ” she said.

Bacon said the area allows for one development of 100,000-175,000 square feet, or any combination of smaller ones. Allowed uses include retail, restaurants or gas stations, all of which would be required to meet design standards.

Whether the property is sold as one or several lots, Bacon said, would be defined in subdivision plans.

“The overall concept of the Innovation District focuses on creating a high-tech and high-quality job center with strong transportation connections and internal network,” Bacon said in a memo to the board. “The area will be walkable and multi-modal with interconnected streets, private shared access ways, and a trail system and greenway to access the nearby Warren Woods’ conservation land as well as future phases of the Downs.”

Further, Bacon said the goal for the area is to be an “employment center,” and it’s expected the Innovation District alone will create around 1,000 jobs – a third of the number forecast for the entire Downs property.

There also will be about 50 acres of open space, 40 of which will be preserved wetlands with 100-foot buffers around the edge of the property, according to Bacon.

He said developers have been coordinating with the Scarborough Land Trust about the preservation of open space, as well as the historic, informal trail at the northeast corner of the property linking to Warren Woods. Bacon said the trail could be expanded to traverse the perimeter of the district and connect to Warren Woods to the east, and include trailheads and parking.

Developers have also met with the town Energy Committee, he said, to discuss potential opportunities for incorporating energy-saving measures and technologies into the district’s development plan in order to reduce costs and energy usage.

Town Planner Jay Chace said the Planning Department will now work with the applicants about standards for commercial retail and light industrial lots, as well as streetscape buffering for parking lots.

Once those details are worked out, plans will go back to the board for preliminary site plan review and final review before work can begin.

“We’re eager to get into the details and get finer grain here,” Bacon said. “We don’t have rules until you agree to them as far as setbacks and lot sizes, so there’s only so far we can go engineering-wise without those rules.”

Board members acknowledged they didn’t have too much jurisdiction over what exactly will go in each lot at this point, but will later in the process as site plans are presented.

“I like what you’re doing,” said board member Richard DuPerre. “I think you’re going in the right direction.”