The project's opponents, however, have not given up.
Even as construction crews begin work on the roundabout this week, residents opposed to it are planning to file an appeal in court.
Jacki Miller, a Swarthmore resident leading the effort, said she worried that the roundabout would cause "inevitable queuing during rush hour."
The intersection at Chester Road near the borough's SEPTA station is already busy, and drivers use Route 320 as an alternate route when I-476 is congested.
The Pennsylvania Department of Transportation, which owns the right-of-way along Route 320, approved the roundabout plans. Swarthmore College will pay for construction.
The borough council also voted to approve the development plans earlier this year.
Borough Council President Ralph Jacobs said the roundabout would improve the safety of a dangerous intersection.
"My view is that there is overwhelming support for the roundabout in the community," Jacobs said. "I think the number of people who are opposed to the roundabout is really a very, very small number of people."
Miller said she fears that the roundabout will slow traffic too much, forcing cars to wait along Chester Road for their turn to enter it, or increasing congestion on other roads in Swarthmore.
"For those of us that have lived with the stoppages on 320 and what happens to the traffic when it sheds through the borough itself, it's not good enough," Miller said.
Stuart Bowie, a lawyer who lives in nearby Wallingford and is involved in opposition to the roundabout, said the appeal he plans to file in Commonwealth Court in Harrisburg would request a formal public hearing on the roundabout. Even though construction has begun, the group says it will move forward with its fight.
Construction on the roundabout will last about six months, said Jan Semler, Swarthmore College's director of capital planning and construction.
The new inn, which also sparked some opposition because it will have a liquor license, is expected to open in 2016.
Swarthmore Borough is dry, but the inn will include a restaurant with a liquor license. A voter referendum in 2001 allowed for a liquor license, but only in a hotel in a restaurant on the college campus. The possibility of a bar in Swarthmore also led to a lawsuit from concerned residents, though a Delaware County judge this year upheld the exception to the borough's dry status.
Jacobs, the borough council president, said there had been opportunities for residents to support and oppose the project at a number of meetings over the last several years.
"I don't think that the inn and restaurant and college store are going to dramatically change the character of the town," he said. "I guess in one sense I think there will be significant improvements, but in another sense I don't think they will really change the positive character of the town at all."