This cut-off route, called the P&T for short, was built in 1906 by the Pennsylvania Railroad and parallels the PRR main line between Frazer and Thorndale, in PA. Running almost 13 miles, and double-tracked, it served local customers along the right-of-way, thereby freeing up the mainline for through traffic. Never straying too far from the mainline, it actually crossed over it via a huge trestle in Exton, PA, in order to serve customers on the other side.
It was abandoned and removed by Conrail in 1989. The mainline to which it connected is still in use by Norfolk Southern.
Thanks to Joe Sharretts for contributing information about this route.