GG,
“and the מנחת יצחק about London, to say that the מחבר does not refer too a literal 600k every day, rather, basically, the מחבר means a street which is מיועד for 600 k.”
Please reference the מנחת יצחק, the one I know of, clearly states that the 600k need to pass in the course of ONE day, though not EVERY day, but they do need to be passing at least on some (consistent) basis and then be מיועד for 600k on a daily basis, meaning they need to be close by, which is the case in Jerusalem, but never pass in a single day.
This is not his own shitah, he is basically quoting the Beis Efrayim, (which is quoted by the Marsham as well…) And so is it clearly the understanding of the Meiri in Rashi’s shitah, that 600k needs to be passing ‘occasionally’ in one day and “possible” every day.
The ‘סברה’ seems to be that if it never actuality passes then it it cannot be defined as a Rh”R of 600k, only once it does pass, occasionally (i.e. not as a one time occasion) , thus can ‘מיועד for 600K’ be defined as 600k – even on the days it does not actually pass, but nevertheless, you still need a road/street with 600k traversing within a single day.. which you do not have…