I find it interesting that this truck bypass is one way—northbound only. So apparently, trucks would be a hazard descending the steep grade into the town streets of Ridgeway, but they're OK to climb that hill. I see there is a truck climbing lane headed southbound out of Ridgway. And even with a more gentle alignment, the truck route still has two runaway truck ramps!
This may be something of an anomaly—I don't think I've ever seen a one-way rural road that was anywhere near as long or close to this level of development. The alignment, grading, and bridges all look like elements from a typical PA freeway from the '60s-'70s era—albeit with one lane.
As to the "NO CARS" bit—I doubt it's enforced strictly. On street view, notice that there's a marked STOP close to the bottom of the hill with a line marked on the pavement, yet the sign still specifies "TRUCKS", even though by this point, trucks should be the only vehicles on the road, and the stop line is in a separate lane on the right—as if to allow cars to drive by without stopping. I'd certainly risk driving on the truck route just for the experience. If you lived in the area, it looks like it would be a very useful bypass route from US 219 North to PA 120 East.
By the way, based on the height of the GSV cam, it looks like their vehicle was violating the "no cars" rule.