Location? Dempsey's Straight Line

In the new Morning Sun book on the Lehigh Valley (Allentown - Bethlehem Region), on page 29, they refer to symbol NJ-6 at "Dempsey's Straight Line". It appears to be a nice tangent. But where? Maybe even in NJ?

Thanks.

That is bewteen Redington and Steel City on the old LV, east of Bethlehem.

Thanks.