@Neville ChaimBerlin
“Gaon: There’s a shittah that the 600K only applies to cities and intra-city roads require fewer than 600K. I don’t know if this has anything to do with Rt. 9. I have absolutely no idea what the “Route 9” situation is that people are talking about, so I’m just guessing. ”
This is argued by the Ramban (Eruvin 59a, and maybe the Tosfos Rid), however we do not paskin like this shita.
However, this can’t be the argument about Rav Aharon and RT 9. Rav Ahron followed the Mishkinos Yaakov who does not accept shishim ribo as a criterion of a reshus harabbim at all.