According to CNN, Turkey and its proxies having cut off the M4 highway, which runs roughly in the east-west direction along the northern border (but in the Kobane-Aynisa sector it's more like northwest-southeast):
shows that the initial Turkish incursion intends to pressure -- at the least -- Kurdish territory over 10 miles further than the 18-mile-deep corridor suggested they would occupy.
But was the highway itself claimed by Turkey as part of their initial "safe zone" map, before their incursion began? If they didn't claim the M4 highway entirely, how much of the highway did they claim for their "safe zone"?
I'm struggling to find a map of the Turkish zone that has the highway superimposed. Most maps just plot the zone over a geopolitcal map with no roads or other features shown besides official borders. According to a Turkish-released map of the hostilities, on Oct 12 they've cut the highway in the El Halidiye sector east of Aynisa, but this map doesn't show their initially proposed "safe zone".
A day later, the Washington Post reported
Ain Issa, which was the headquarters of the Kurdish-led administration in northeastern Syria, owes its significance to its position beside the M4 highway, which runs from the Iraqi border across northeastern Syria. [...]
Turkish-backed rebels have set up checkpoints on the highway near Ain Issa, cutting off U.S. troops in bases to the west, in Manbij and Kobane. Those troops came under Turkish artillery fire Friday night in what some U.S. soldiers suspect was a deliberate attempt to drive them away from the bulk of the U.S. forces farther east, Kurdish and U.S. officials said.