Don't forget it's straight line distance too....even if you would have to run a triathlon to get there that way....
Yes it's nonsense, but easier for the folk at the LA.
The alternative being the 'safe walking route' or whatever it's called, which is what our catchment comprehensive uses - or at least did at least as recently as DD's year. It could have changed but it was irrelevant for DS2, fortunately. When I saw in the following year's Admissions booklet that the last child admitted other than on appeal was a non-sibling living 2xxx metres from the school, I couldn't understand why DD hadn't been offered a place, but then I realised that it used a different measure of distance from all the other schools in the Borough.
Possibly a better measure where there are natural features to circumnavigate, though - like the Thames. In a very low birthrate year, I suppose one of our DC might qualify on straight line distance for a school in Medway, say, when the actual daily commute would be an 80-mile round trip by road or 2 and a half hours each way by train
Since joining the Forum, though, I have learned that not everyone would necessarily allow their DC to be put off by this...