All perfect praise be to Allah, The Lord of The Worlds, and may His blessings and peace be upon our Prophet Mohammad and upon all his family and companions.
Sharia doesn`t permit exhuming or removing graves so long as they contain bones because the sanctity of their dwellers is similar to that of the living. In Jordan, it is well known that the bones of the dead need very long time to turn into dust. Prophet Mohammad(PBUH) said about the sanctity of the dead: "Breaking a deceased body’s bones is exactly like breaking them when he is alive.” {Related by Abu Dawud}." He also said: "It is much better for one of you to sit on a live coal, which will burn his clothes and get to his skin than to sit on a grave."{Muslim}.
These narrations highlight the sanctity of the dead and that preserving their graves against harm is obligatory because Allah, The Almighty, said: "We have honoured the sons of Adam"{Al-Isra`/70};
Therefore, not exhuming graves and not violating their sanctity is honouring their dwellers. As regards the above question, being adjacent to the main street isn`t a valid excuse for exhuming that grave since it was dug up with the blessing of the owner of that lot of land, and it is forbidden to widen that street at its expense; rather, its sanctity must be preserved.
In conclusion, it is forbidden to exhume that grave unless the buried person has turned into dust. And Allah knows best.