If you are concerned about the factory edge, that's the first issue. I understand it's a common practice to take your biggest track and cut 1/8" from the full sheet of plywood. This new edge becomes your 'reference' for straight and you can use it to make accurate parallel cuts and 90-degree crosscuts. (This presumes that you have the first long track and a really good 90-degree crosscut tool.)
Once you have a known good edge, Woodpeckers and TSO certainly have beautiful track saw parallel guides that link with any standard track to make these sort of consistent, repeatable cuts possible. They are a little pricey, but if this type of cut is a regular thing then they are fantastic to have. You can get into the whole "Do I even need a table saw??" conversation.
I have made my own parallel guides for repeatable track saw cuts - got the plans from
Warrenton Woodworks. The premise is quite simple - if you can make something that has a hook or stop to connect with the good edge, sits at 90-degrees to the good edge and references with a clean connection to the track saw guide, and has a consistent length (you can match a pair of parallel guides together, as
Warrenton does here), then voila - you have a parallel guide.
The TSO Parallel guides are very sexy, and when they are calibrated correctly, it's delightful to set the measurements, walk over to your plywood, and then slap it down and make the cut. But it's also possible (as
Packard suggests, above) to use a basic measuring stick similar to the Warrenton solution. This would be kind of a 'story stick' for the track saw - just with two of them.
- Create your clean reference edge on the plywood.
- Mark your measurement of 16 inches - and then set the track on that measurement.
- Poke one of your measuring sticks against your track to set the first part of a 'parallel' set.
- Set your second measuring stick against your first measuring stick, to exactly match lengths.
- Use the pair of measuring sticks to lay your track down, parallel to the clean reference edge.
- Cut your piece. Repeat for additional pieces of the same width.