The Pennsylvania Turnpike Commission says Thanksgiving is most likely going to be the busiest travel holiday of the year. Officials said yesterday that three-and-a-half million cars are expected on the Turnpike between Tuesday and Sunday next week. There is no scheduled maintenance or construction and all lanes will be open. The busiest travel times are expected to be Tuesday from 3:00 until 8:00 p.m., Wednesday from 7:00 a.m. to 8:00 p.m. and Sunday from noon until 8:00 p.m.