A quick look at the maps Yani provided leaves you with several possible routes through the Awakened woods and post-glacial hills that managed to force TriCity to grow north, south and east, and abandon it's western areas...
You'd have to reach the remains of the old highway circling TriCity, and go on foot from there. Through the woods, avoiding hilltops and keeping as low as possible to avoid any nasty critters. There are more than a few streams available this time of the year, and you can use them to your advantage. Your only problem would be Barghests and Stone Toads, and only the former would be any problem. It's unlikely that you would encounter them closer to the city, and they're mostly solitary except for the mating season. Which is in early autumn, so you don't think there would be any problems.