We lived within sight of the M40 for a bit - probably about 500m away too. I didn't mind the noise in the house, and the house was between us and the road, so the back garden was fine, and I did get used to it and not mind. The front garden was very noisy sometimes though - loud white noise.
Another time I lived within 50m of a busy train line, which made the house shake, but there was a heavy wood (think 1 foot thick) sound absorbing fence between so the noise didn't bother me at all.
Yet another time, I was again within 50m of a motorway, and the car noise was annoying in the back garden - noisy enough that we couldn't hear each other very well at a BBQ, and more than once I heard a crash in the middle of the night which can keep you awake thinking about it. The main annoyance was the lights shining in the bedroom window though.
Right now I'm within 1km of a busy main road, no fences, and it's at the bottom of a valley while we're up the hill a bit so all the sound seems to bounce back at us. I don't mind it at all, and in fact quite like just sitting watching the cars go by.
I would say that if it's continuous loud white noise in the back garden, and you're a person that wants to use the garden, that's the only thing that would put me off, although a proper fence might mitigate it if the road is low enough (I imagine they're quite expensive though).
If it's a quieter, background noise, then you won't notice it in the house, and you'll probably stop noticing it in the garden.