Looking at this image, you can see it technically isn’t curved. It is segmented with straight parts that are rotated to achieve what looks like a curve. If you want to be able to manipulate curves in this fashion, then I’d recommend stitching together straight parts to form what looks like a curve. similar as to how an octagon looks more like a circle than a square.
Alternatively you could try to use cylinders if you really want a smoother curve. But that would mean you have to not only measure out how big or small the curve would be, but also negate and union more pieces to suit your looks.
TL;DR Use small segments and turn them slightly as you move along to achieve what looks like a curve.
 Manually make a road segment and make the road segment and adjust the size so it is a bit thin, probably thin as 4 studs. Next, duplicate it and rotate it 3 degrees a few times and you should be able to get a perfect road