It isn’t obvious Donclark, but a lesser speed would mean a greater njumber of cars. Why, because of the terrific reduction in STOPPING DISTANCE! “Bumber to bumper traffic” usually means 15 miles ano hour with cars about 12 feet apart. At 22 miles per hour cars space themselves about 1.5 car lengths apart. At 30 miles an hour, and in agreement with your calculations, about four car lengths apart, at 60 miles an hour about 12 car lengths apart. So 22 mph is the optimum speed if all you want is to get the maximum number of private cars passed a given point safely.