First, no one calls it "the Mon-Fayette Expressway." It's just "the toll road."
Second, the toll road is the fastest way between my apartment and my parents' place, as well as one of the fastest (though least interesting) routes between my parents' and work. But I almost never take it. From my apartment, at least, taking the toll road means paying twice--I believe about $1.90 in the Nam and $0.99 in near Washington. I need quarters to do my laundry and don't typically carry much cash, so I pretty much only take the toll road if I have some dollar bills or am traveling with someone who does.
It's a nice road to travel, though. You can go fast, and almost no one is ever on it--probably because of the tolls. Obviously, more people would drive it if they were lower, and then whoever gets all that money would be making bank.
The other problem? It seems like nearly all Fayette County exits are labeled "Brownsville." Do you know what a pain this is when I can't really tell where in the Nam I am from the toll road and want to go to Uniontown and not Brownsville? The last time I drove the toll road to the Nam, I was trying to find the exit that would get me closest to New Century Buffet, but they were all labeled Brownsville. I didn't really want to get off the toll road to drive another 15-20 minutes into town from Brownsville if I knew staying on the toll road would get me there faster...but I didn't know which exit would take me to Uniontown and didn't want to stay on too long for fear they all just say Brownsville or I'd somehow end up past Uniontown or even have to pay a third toll.
Turns out I had to pay a third toll anyway and probably would've gotten to the buffet faster if I'd held out for one or two more exits that may or may not have said they go to Brownsville.