Question:
May one drive from one township to another on a date if he must drive through a highway to get there?
Answer:
If there are cars constantly on the road there is no problem of Yichud.
Sources:
Teshuvos MInchas Shlomo 1:91-21, Igros Moshe E:H 4:65-3, Tzitz Eliezer 6:40 Chap.15