What is this "Frontage Rd" I see on I-10?

Question

I live in San Antonio, and I am a dude with highways.

I will describe these locations. First, from Huebner bound to 410:

If you enter from Huebner or DeZavala, you will see an exit sign that says, "Frontage Rd." This is seen from I-10 East.

From I-10 West, bound to 1604:

After UTSA, around the transfer to 1604, there will be a sign saying, "Frontage Rd Park & Ride." This is from I-10 West.

Now, I see no street sign or anything, so what is this so-called Frontage Road?

Answer 1

Frontage roads run alongside most freeways:
http://en.wikipedia.org/wiki/Frontage_road

"Frontage roads provide access to homes and businesses which would be cut off by a limited access road and connect these locations with roads which have direct access to the main highway."

Answer 2

Its the road that runs alonside the freeway, not just on the I-10, but anywhere.