With the advent of controlled-access and limited-access highways, the rest stop was created as a conveniently accessed facility for drivers to rest along long trips. Most rest stops seem like a regular exit from the highway, but have no access to other roads -- simply ample parking for trucks, buses, and cars along with a variety of things travelers may need.
While most rest stops are glorified parking lots (often adding only a public restroom and potentially some vending machines), some localities spruce up their rest stops with park-like open areas for recreation, picnic tables, and charcoal grills. These amenities are for truckers and traveling families alike. Often charter buses will pause to take advantage of these resources to break the monotony of a long trip and allow the passengers to interact with someone other than their seatmate.
On rare occasions, rest stops are enhanced even further. Along New Jersey's Garden State Parkway, "rest stops" are massive islands between the two travel directions where visitors can find gas stations, restaurants, convenience stores, and sometimes entertainment (in the form of video arcade games and the like) -- all with the convenience of easy-on, easy-off highway access. This formula has been emulated on many other highways with great success.
With Americans' addictions for driving, some transportation departments have utilized rest stops to help lower risks associated with continuous driving for long periods of time. In Ohio (the first place I have witnessed such an offering, but undoubtedly it is elsewhere), community service groups man booths where free coffee is available to drivers through the night. These booths sometimes also offer snacks and other travel supplies in exchange for a modest donation.
In North Carolina, the Department of Transportation has advanced rest stops into an art form. Most are tastefully wooded, placed in convenient locations where regular services are not available, and offer clean well-lit facilities. Upon parking, one can walk into a temperature-controlled building with automatic sliding doors, utilize the restroom with entirely automatic plumbing, and examine a variety of maps and travelers' information in a well-maintained and well-patrolled environment.
On your next big road trip, don't forget to take those few minutes to visit a rest stop you may not have visited before. You might be surprised by the innovations it offers in convenience! And you never know, you might learn something.
This writeup is dedicated to Leon Marconi, and I hope it alleviates some of his confusion.