What does "that" mean in this sentence?

Question

turnpike

noun

a wide road, where traffic can travel fast for long distance and "that" drivers must pay a toll to use

^{(Oxford Advanced Dictionary)}

What does "that" mean? Is it a relative pronoun? Must drivers pay a toll to use a wide road?

Answer 1

Yes, it's a relative pronoun and is pointing back to the subject "turnpike" (or perhaps "a wide road" -- it's not exactly clear since, being a dictionary entry, the whole thing is made up of sentence fragments). You can see its purpose more clearly if you split the definition into its three constituent parts:

1. A turnpike is a road that is wide.
2. A turnpike is a road that is useful for traffic traveling fast and for long distances.
3. A turnpike is a road that drivers must pay a toll to use.

Answer 2

It's a pronoun, acting as the subject of the relative clause "that which drivers must pay a toll to use". Here, you could equally well use "which". It means that the previously mentioned road is the thing drivers must pay a toll to use.

It's much the same as "the book that I read".