- Its not that I question the conclusions reached concerning the Michelson–Morley experiment, however I would like to know how the following issue was addressed please?

If I could pass bob through a beam spliter, and have each copy of him pace out each leg of the interferometer at say $2km/hr$. However if along one of the legs, there was an escalator aiding his initial progress at $1km/hr$. 

Ok, so they each leave the beam splitter at the same time, however aided by the escalator one of them moves at $3km/hr$, and reaches the mirror at the end of his leg earlier than the other. But on the return journey he is inhibited by progression of the escalator, and moves at $1km/hr$. So the other bob who traveled at $2km/hr$ the whole time, makes up ground on the other bob on the return journey, and they arrive home at the same time as each other.

- With so many clever people working on this experiment over the years, I know there must be a contingency for this issue. If somebody can inform me please? 

It will be immensely helpful for me