Matthew Bates was active on Lugnet in the late 90's and early 2000's when Lugnet was the one place for Lego discussion. It was probably my most visited website during that time. Version 2.0 of Track designer was released in 1998, so its almost 30yrs old!
In late 2004 someone posted asking for the source code. Then in 2008 Matt found it and was discussing the idea of releasing the source code, you can still read it here (but the webpage is now, almost cancerous with its advertising popups) LEGO SYSTEM Trains : 22776 (lugnet.com)
At some point after that, the ownership of the program was handed over to the North Georgia Lego train club, which you've linked to already. I suspect it's never been developed any further, and there are now other options available that are probably more suited to modern operating systems.