This is a good start.
You might want to make your chapters a little longer.
You should have also made Severus a little more reluntant in going to get Harry.
You need to explain why Severus took the Knight Bus instead of apparating to the nearest apparation point.
There was not enough anger displayed when Severus confronted the Dursleys.
More dialogue is needed.
Why is it that when Albus suggess that Harry needed to be taken from Number 4 that it is Severus (mostly) or Hagrid (or even Dumbledore sometimes) are the ones that pick him up?
There are other teachers at Hogwarts and ex or current order members that could pick him up and take him away.
Good start. Update soon.
Author's response
why thank u and i will improve the story