Not a huge difference. I would say it’s the main route (or routes) or primary route between two points. So, for example, a road that simply goes around the neighborhood I would not consider a thoroughfare, except to my neighbor’s house (but you wouldn’t use that really in this context except maybe in a joking manner). Whereas a more traveled road or highway to my friend’s place across town could be considered a thoroughfare… Or the main highway between two cities.
Here’s the dictionary definition:
1: a way or place for passage: such asa: a street open at both endsb: a main road
2a: PASSAGE, TRANSITb: the conditions necessary for passing through
Other comments are a good explanation. I add that the word “thoroughfare” is more focussed in the fact that this road is “a way through an area or areas” on the way from A to B. In contrast, some streets just end and you have to turn around. I word “thoroughfare” basically indicates you can go “through”
I’d say no. It is mostly used when you want to emphasize the particular quality of a road/street/highway being a thoroughfare.
“Take a right when you get to Elm Street. You can’t miss it, it’s the main thoroughfare.”
In face, most of the examples I can think of use “main thoroughfare”, just like your example.