You chose two competing minor subjects to highlight - line and curve. They compete because the line is a lighter shade of yellow from the brighter sign. Could be natural - it should have been corrected in PS so the two items complimented each other. Either desaturate the sign a little or increase the line's saturation a bit and it would have helped immensely..... that, and leaving the sky intact would have added balance. However, the road is your main subject in this picture - by highlighting the two minors it's only caused confusion. The road being black is already highlighted by the colors in the original picture - desaturation only made it blend in. This is not a good choice of picture to use in a desaturation challenge.
You have an excellent compositiion and have exposed it very well. It has a nice "country" feel to it. I can't decide if I would like it better with either the sign or the yellow line in color, but not both. A very minor annoyance is the 2 white dots on the left edge (headlights?) Strong submission that should do well.
I really like this shot and a lot of us are making hard choices of what to emphasis (some for the first time). While I like your choices of yellow placement, I wonder what this image would have looked like with the 40MPG and the two other lines emphasised as well. Naturally, I assume you already looked at those ideas and made your decision but if you haven't, it's something to think about.
I really like the way the two yellows tie together, a very effective use is selective desaturation I think.. You could have made the photo a bit larger and sill been in the size limits, larger photos seem to do better on DPC.