can not upgrade the road

@jasonkokoko  I think you may have a “fun” challenge on your hands. It appears that you may have one or more buildings that are oversized for the area they are in and will not allow the road to expand (an example would be city storage). The challenge is you have a long section of road to work with and I suggest you break your road into incremental sections such as 4 or 5 buildings in length - to do this you will need to remove and save a park or building and place a temporary small side road (one section only) which creates two sections of the existing road and allows you to expand a smaller section. Once the side road is in place try expanding the newly created smaller section of road - if it expands correctly delete the side road and replace the park or building you previously saved.

Continue this process until you reach a section you can’t expand - if the road won’t expand and there is still additional road left above the side road try expanding that section and more likely than not it should expand properly (if not continue putting in temporary side roads). Assuming the above section expanded correctly you have effectively narrowed down your problem to 4 or 5 buildings...take a very close look at this section and see if one of the buildings has a little larger base than the others. If so, create a space in your city and relocate the building and then try expanding the road section and if it works that’s the problem.

Often the building you had to move is more desirable where you had it located but unfortunately the footprint didn’t match once you had to expand the road. I suggest you make sure to expand the section of road in front of the new location of the building to its maximum potential (place temporary side roads either side if an existing road is in place) so you will know what you have to work with space wise in that section of your city.

Sorry for the length, hope it helps. Good luck.