Jogger2
In my opinion, that's correct. There are several "Frontage Roads." A frontage road is a road alongside a highway that allows access to properties bordering the highway. 

Suppose there were two north/south highways, each with frontage roads. Then, an address such as "12345 West Frontage Road" would be ambiguous. It would be necessary to say something like "12345 Frontage Road Highway 987". So, AFAIK, it preferable to not say "Frontage Road" in the address, but to specify the highway.