We have three on one road literally within one and a quarter mile.
They've been here for fifteen years and they all do a good business. When the Speedways close the one left (currently the middle one) will be inundated. There are many other areas with stores close together as well.
Here's a quote from Cape Cod Times reference DD in Hess stations (July 17, 2015):
"Marathon is still expected to provide gasoline to all the Cape Speedway and Hess locations, and the Dunkin’ Donuts kiosks that operate inside many of the stations are expected to continue providing coffee and food service to customers – at least for the time being.
"We are still in the process of evaluating the viability of these quick-service restaurants," Griffith said."
Speedway, Marathon, has decided not to continue with DD in its convenience stores. That's all. Some DD stores though are so close to one another that the remaining store(s) may not be able to handle all the business.