1.) I didn't really notice the environment changing to show time until I saw the question. It does read as something changing but I wouldn't have guessed it was the sun setting. Maybe add an indicator of a Sun setting to the background?
2.) I like the road width as it is, and found it amusing that you can drive into opposing traffic :P
If you wanted to fill up the screen, you could add trees and other sprites to decorate the empty space a bit?