Jacksonville including all of Duval County has a density of 1,133.9 people per square mile. Atlanta might have a density of 4,019.7 ppsm, but the Atlanta Metro Area, roughly analogous to Duval County (the extent of JTA) is actually 629.4 ppsm.
Truth be told, there really is no formula of density = schedule headways. The fact is the supposed formula is trotted out by the anti-transit crowd to prove that (name any project) won't work. Every single city and every MSA has it's own unique set of population v mobility challenges. Take Orlando for example, because of lakes, 4 onetime military reservations and insanely rapid growth, you have a metro of 2,000,000 plus, with what amounts to a single main highway. It really doesn't matter how dense the population is along the east or west edges of Orlando, if your going north or south, where the main employers are, your going on I-4. Though Orlando's density is 2,134 ppsm, that entire population is forced into very few extremely crowded corridor. Atlanta has the same type situations, nobody is building apartments on top of Stone Mountain, Kennesaw Mountain, Sweetwater Creek State Park or Lake Lanier, thus each corridor around those places is likely to be much denser then the average square mile of ground.
Some cities that are much smaller might have highly successful transit operations, St. Augustine, Gainesville and Stillwater, Oklahoma are just 3 examples. Note that I didn't say 'profitable' or 'cover the cost of operations,' successful equals popular, punctual, clean, efficient, progressive, aggressive, in-demand, welcome and welcoming, mass transit. Gainesville and Stillwater both operate in cities dominated by major university's, St. Augustine has a large centrally located college and just short of 7 million visitors a year, tourism that creates a demand for thousands of service level jobs. Success isn't so much that these cities have been somehow 'blessed' with a successful 'excuse' for being winners, as it is that they recognised these demographics and responded to them.
Jacksonville grew up on the railroad, even as a teen in Jacksonville there were little flag stop stations all over the county... Greenland, Bayard, Sunbeam, South Jacksonville, Yukon, Springfield, Whitehouse, etc.. Further the city has grown up around it's river port and it's military presence creating unique crisscrossing corridors connecting the dots and strung along railroad lines, past (such as Atlantic, Beach, Wonderwood) as well as current. Our US Highways and our Interstates ALL follow historical railroad corridors. Lastly you have to factor in the miles and miles of nothing between Cecil Commerce Center and the county line near Callahan, or the miles of empty marsh between Little Talbot Island and North Main Street. Using our historic corridors as your measure and you come up with a much denser city, denser in fact then many cities with rail based metros.
To over simplify the problem in Jacksonville, JTA simply has failed to respond to the needs and historical travel patterns in Jacksonville. Ultimately JTA fails across the board, it is not popular, punctual, clean, efficient, progressive, aggressive, in-demand, welcome or welcoming.
Is there a demand for a dedicated express bus between the Nuclear Submarine Base at Kings Bay, and Mayport or NAS Jax? Does anybody at JTA even know where Kings Bay is at? How many times have we met with RTS from Gainesville and Greyhound Lines to discuss a real connection between Shand's and UF? Does JTA know that Camp Blanding is no longer a sleepy home for weekend warriors and does in fact train Army, Marine and other units of our military? JTA laid out 90 miles of commuter rail, how many of those miles currently have dedicated express buses? Can I get directly from UNF/Town Center/Baymeadows to Orange Park? Can I get on JTA and get off in downtown St. Augustine? Green Cove Springs? How about Julington Creek Plantation? Nocatee? Fernandina Beach? Middleburg? Are St. Augustine buses welcome into downtown Jacksonville? Locally can I get from NAS to Cecil or Mayport on a single coach? Bus? How about NAS to anywhere on a single bus? How often can I get to Cecil Commerce Center, Aquatics Center, Equestrian Center, or the Zoo? Can I ride directly from the Library to UNF, JU, FSCJ and Edward Waters? Mandarin, Lake Forest or San Jose to the Beaches seamlessly? If not why not?
JTA fails largely because the same clueless managers, directors and planners that brought us the failed and incomplete Skyway, The Southbank Parking Garage, and plans for a Vatican City sized Transportation Center, continue to bumble along with false starts, wasteful practices, and a 'CYA' business plan. With the exception of a few newer faces, the entire organization should shift to highway planning and the city should create a responsive mass transit agency with those few bright stars at it's center.