I made a slight change to my daily commute between Baltimore and Flint, Michigan yesterday in order to bike the Heritage Rail Trail County Park, which runs from York, Pennsylvania to the Maryland border in New Freedom. There, it connects to the Torrey C. Brown Rail Trail (formally known as the North Central Rail-Trail), and continues into Maryland.
Truckers, there is a nice small truck stop at the Shrewsbury-New Freedom exit on I-83 where you can park. From there is it just over a two mile scenic and hilly hike or bike to the Heritage Trail. The portion of this route closest to the interstate is congested, but the traffic lightens up quickly as you move towards downtown Shrewsbury and towards the trail.