Danbury is considering zoning changes that could speed approval for fast-food restaurants along Mill Plain, Federal and Newtown roads. Under the proposal, chains in those commercial areas could receive administrative approval without a public hearing. Restaurants expected to generate at least 500 car trips a day would still face additional review. The changes would also ease some rules for existing restaurants, including limits tied to the number of tables. The Zoning Commission could vote as early as late October.