Though what I am about to write seems rather obvious, I am pretty sure there are people out there who've made this mistake. If any of you do choose to upgrade your roads, please upgrade outwards and not inwards! What I mean by upgrading outwards or inwards is to take your city hall and make it your HQ, the very centre piece deciding your upgrades. The very simple reasoning for this is the fact that the roads have to be connected to your city hall in order for it to be valid for your upgrade!
So let's say you want to upgrade a building and you hover your mouse over to the "Upgrade" icon. You will notice that it says "blablabla. . .you need a Q(x) road between this building and the hall.", where (x) can be any number depending on the level required. What this means is that you need every road stretching from the city hall to that particular building to be upgraded to a specific level before you can initiate that upgrade!
So don't make the mistake of upgrading inwards to your city hall as the roads will be deemed useless until it is connected to your city hall!