Are you open to a segmented curve?
The chart view above illustrates how spacing and radius plays into how well a segmented curve does or doesn’t work. The first two segments are near curve but straight angled lines. The third is more obvious because it has a tighter radius. The other way to control the 3rd segment would be to use narrower spacing.
FYI, the majority of bridge beams are segmented on “curved” bridges. Depending on the exact radii, sometimes the beams will be segmented and the deck is formed and poured on a radius creating variable width overhangs but many times the deck is also segmented. Most people don’t notice because of the spacing and radii used.
You could control some of these factors. For instance your existing pic looks like 12 tiles wide. I assume those are 12” wide tiles. I definitely would NOT use the wider 18” tiles for your new Racedek as it would work against you. And I might consider a free flow tile as it has the optical illusion of being 6” wide. Also if you kept the radius but made it more flat then the segment would also look smaller.
I would use a free/trial CAD software to lay things out with your specifics to see what works or doesn’t.
Also I know you like your setup but having an open mind might yield a design you like better. Below is one example where it would be easy to visibly separate an area (also shows the effect of the free flow tiles I mentioned earlier).
If you end up with a hard transition I would consider a brushed aluminum plate or possibly a black diamond plate transition cover. It would add some interest and look cool IMO. Black diamond plate with stainless torx head recessed screws may have a particularly nice effect.
