My initial image of camels and date palms was way off kilter.
Also, the infrastructure necessary to allow occasional service vehicles to traverse both sides is considerably lighter than a full-blown interchange - but if it was opened to the public, they would try to use it as an interchange.
On toll roads, rest areas usually have a gas station and a restaurant or two (the NYS Thruways stops have multiple restaurants). Parking areas also exist, but have no services at all. The idea was that it was more convenient for travelers to stay on the road instead of exited. Most rest areas on the NYS Thruway and Mass Pike are designed so the drivers exit on the right, not on the left; most areas (except New Baltimore and Ramapo-Sloatsburg) only service traffic from one direction.
Now that is an interesting arrangement, one where the turnpike authorities did have to go out of their way to keep people from being able to reverse direction quite easily. Never seen one like that before.
It’s easy to get confused as to which way to go after stopping for a while. Most people are in foreign territory. There are times when I exited a freeway to a town or shopping center, then was unsure which way to go to return. If you don’t have the choice, you can’t make the wrong one.
I too had no idea what the OP was referring to, but I found this:
Googling does not term up much use of the term anywhere else, so it seems to have a meaning specific to Illinois.
A Rest Stop is certainly a generic name for a place where a driver can pull off the road for a while, but some are no more than rest rooms, parking areas and racks of maps or tourist guides. They can serve to bridge the gap between towns in the sparsely populated Western and Mid-Western US.
The ones on the Illinois Tollway (which connects 3 states) are more elaborate, and include gas stations, restaurants, gift shops, and other motorist services. AFAIK, they are all designed with most services on a bridge across the highway so they can serve both sides, but only pedestrian traffic can cross from one side to the other.
I think the idea was to provide necessary services without having to exit the tollway, which makes a captive audience and avoids the need for toll collection on and/or off the system. It’s nice to be able to travel a long distance and not worry about being unable to get gas or what exit to take for food and be able to return. Believe me, if you exit on a random ramp in Chicagoland, getting back on can be nearly impossible without a GPS or a lot of guesswork and patience.
The Oases were a great idea when they were first built in the 1960’s. I remember the original Fred Harvey sit-down coffee shops and restaurants, now replaced with MacDonald’s, Burger King and Starbucks.
You wonder why? That is your Wonderwall. 
This is all I could think of while reading this thread:
Sorry to be of no help whatsoever.
It turns out that the official name for the large areas with multiple fast food restaurants, stores, restrooms, and a gas station on the New York State Thruway is travel plaza.
Turnoffs with parking and emergency call services and probably a vending machine or two but no gas or restrooms are parking/rest areas.
I’ve never heard “travel plaza” used in casual conversation. It would be “rest stop,” “rest area,” or “service area” or something even more informal, like “pit stop” or “rest place” or “the restaurants.” Wikipedia’s main entry is for rest area. It starts “A rest area, travel plaza, rest stop, or service area…” Resto, and lay-by also redirect there. “Lay-by” is from the UK. “Resto” is mysterious. Oasis is nowhere to be found, even on the disambiguation page.
The logic for them seems to be pretty universal. The New York Thruway had “travel plazas” from the beginning, I think, and that would be the early 50s. Toll roads have captive customers and they are often strangers entering territories they couldn’t be expected to know anything about. In the days where a AAA trip-tik was a big deal, having to exit a freeway was an adventure into the unknown. People wanted to stay on the big, proper, numbered route and not have to deal with inconveniences. That included having to pay tolls out of pocket for each exit in the days before EZ pass. Of course, you paid for the convenience: everybody still complains of the higher prices and lower selection inside a “travel plaza.” Their usefulness meant that they were copied when the non-toll roads were built outside of the pioneering routes in the northeast.
I’m about 99% sure that the reason you can’t turn around even in a non-toll oasis is to keep drivers from going out the wrong exit accidentally. As somebody said, you’d get at least an order of magnitude more people doing this than doing so deliberately.
I never heard of an oasis except for a desert waterhole that guys with camels visit.
What a strange term for a highway. What does a highway oasis look like?
links have been provided in this thread.
A lot like this:
http://www.highwayexplorer.com/Photos/Intchg/I294--HinsdaleOasis-V7.jpg
http://harvey-house.info/yahoo_site_admin/assets/images/Oasis-5b.143105452_large.jpg
http://www.loopnet.com/Attachments/E/0/4/xy_E041DBD5-8E3D-4EFA-80E4-4FFCF839CC33__.jpg
As a counterexample, I believe you can turn around at the large rest areas along I-95 in Maryland. This one, for example. I’ve stopped at these areas the past several years while taking my son back and forth from college. I have not, however, actually turned around at any of them.
This is pretty much what I was going to say. Overpasses tend to occur where the traffic demands them, either at a town or city or where another highway or street needs to cross the freeway (using US terminology). As a result of the increased traffic, that’s where you’ll also find commercial uses of property, e.g. restaurants, gas stations, quickie marts.. By building rest areas in the middle of nowhere, the government can make use of otherwise unused land, i.e. inexpensive.
I love rest areas. They’re convenient as you get directly off the interstate, park for a while and get directly back on. With trees and grass they’re more pleasant than the Denny’s parking lot. I always thought someone should write a guide to Interstate rest areas and of course someone already has.
The only thing more efficient for a quick bathroom break is an empty Gatorade bottle.
In my experience, a wide spot on the road with a gas station, a couple of fast-food joints, a souvenir shop, and restrooms is a “service plaza”, and a place with just restrooms and maybe vending machines and a big map on the wall is a “rest stop” (though the term “rest stop” can apply to either, in the right context). I’ve never heard of one that just has a parking lot with no restrooms at all, though sometimes the facilities are just outhouses.
Some of the Rest stops along my state’s Interstate have been a source of crime. Drug use and gay hookups. They closed the restrooms at one on I-40 for awhile because it was used so much as a gay hookup. i think its open again now. The state police are patrolling the rest stops more often.
I can’t recall any rest stops here that had any stores or gas stations. We have lots of exits off the Interstate with stores, but they usually have a bridge to cross over the Interstate and reverse direction.
There have been times I’ve had to drive ten miles before I could double back after missing an exit. I hate that. So frustrating, especially on trips on unfamiliar roads.
If I could only teach the dog how to do that I would only have to stop for gas.