at front /on front

[Unregistered]

people are entering a bus that has front doors and back doors
which one is correct

let me in on the front and not the back
let me in at the front and not the back

[MikeNewYork]

people are entering a bus that has front doors and back doors
which one is correct

let me in on the front and not the back
let me in at the front and not the back

I would use the second.

You could say, "let me on in the front."