What are the major differences in S1 and S3 asphalt and what would typical applications be

These are not designations I have seen with highway paving. Possibly an architect or engineer made their own reference on plans or specs. Or it may be something new although I couldn't find it in any search.
Asphalt is used in many applications such as paving, roofing, sealing, plus many people refer to asphalt when describing hot mix asphalt (with stone for driveways and pavements), while others are just referring to the basic liquid before any mixing with aggregates. One possibility is sealing material as described below:
Asphalt Paving Sealer: Saving the Driveway Track from Cracking (http://www.buzzle.com/articles/asphalt-paving-sealer-saving-the-driveway-track-from-cracking.html)