I-81 remains very similar to when it was completed in 1966. Exit numbers were first marked in 1974; these exit numbers have not changed. The Maugansville Road interchange was originally a full interchange, but it was reduced to a partial interchange in 1968. The interchange with MD 68 and MD 63 south of Williamsport originally only had a northbound exit ramp and a southbound entrance ramp; ramps to and from the direction of Hagerstown were added between 1981 and 1989. The junction with Halfway Boulevard was a diamond interchange until it was rebuilt as a partial cloverleaf interchange in 2001.