The actual use of toll roads is not typically seen as price gouging. In general, tolls are not so high as to qualify for this (unscientific) term. One could argue that the new trend towards "congestion pricing" where drivers must pay higher tolls to drive at peak hours or on popular roads is a form of price gouging. Since there is no technical definition of the term "price gouging," anyone can argue that any price that they think is too high constitutes "gouging."
One thing that is sometimes seen as price gouging is the prices that are charged by restaurants and gas stations at rest areas on toll roads. At times, gas stations or restaurants in these areas have charged prices that some see as excessive because drivers have little choice about where to stop. Since they are on a toll road, they can either stop at these rest areas or have to get off the toll road and later get back on, paying the toll again. These rest area prices are typically higher than those in areas not on the toll road. Many people see this as price gouging.