In the northern valley, the thoroughfares vary. Heading northeast from Harrisburg, I-81 traces the valley to Swatara Gap, then swings north across Blue Mountain and leaves the valley en route to Scranton. I-78 then continues the route through the valley parallel to the southern slopes of Blue Mountain, connecting Harrisburg with Lebanon, Kutztown, and Allentown. At Allentown, I-78 then swings away south into the hills of the Reading Prong en route to New York City. From Allentown into New Jersey and southern New York, the valley is not traced by an interstate highway, though it is traversed at length (and at oblique angles) by both I-80 and I-84, as well as by the Delaware River between Easton, Pennsylvania, and the Delaware Water Gap.