The highway then became signed as State Route 48 until the 1964 renumbering.

Since December 2009, the highway has been signed in the field.

It is unclear whether or not this highway will ever be signed.

The highway was signed in 1927 from Pittsburgh to Kittanning.

The highway was first signed in 1923 on much the same alignment as today.

However some highways are shorter but are not signed at all.

The highway was originally signed as Pennsylvania Route 45 from 1927 to 1966.

The highway has never been publicly signed as 400A.

The highway is signed and mapped as State Route 21.

The highway was first signed in 1923 and was much longer than it is today, going to the Michigan state line.