That was my first thought, that the radio buttons had to have the same name.
I've just tried your edits, and that resulted in the results displaying both cars and vans, no matter what was selected.
But strangely, I made copies of the relevant pages, and I was sure it worked with the new pages.
Then I resaved them back with the original file names, and they stopped working.
So at the moment, I have a new index page with your edits, showing it just selecting cars and vans :
And its all very odd anyway as I'm sure it did work originally.