A: Listen – is this right: ‘I live on 99 Bishan Road’?
B: No, that’s wrong! You live in 99 Bishan Road.
C: Both wrong! You live at 99 Bishan Road.
Who is right?
The problem is that there are different ways of looking at the same location. But C is right. At is used when street numbers are mentioned because we think of a particular point along the street, namely No. 99.