Hi Deb,
We're a rural shelter located about 30 minutes outside of our major metro areas so our issue isn't quite as severe as a 90 minute drive, but some of the things that have been helpful for us:
We have a satellite adoption location at a PetSmart in one of our metro areas. It would probably be tough to do something similar with a 180 minute roundtrip for you, but if you can participate in monthly or quarterly adoption events that PetSmart, PetCo, and other pet stores host, that might get you some more exposure. Typically those events allow you to bring more animals and don't happen as often as refilling a permanent adoption center, so it'd be more time effective.
We were also able to get on the rotation with one of the local news stations for their Pet of the Week. If any of your station affiliates (ABC, NBC, CBS, FOX) do that sort of thing it might be worth a call to see if you can get in there. If not, sometimes the local radio stations do the same thing.
You're probably already doing this, but definitely expanding your network on social media to include adopters. As you build up the network, posting potential animals there will give you a wider net for anyone connected with your followers.
If you're not already looking at open adoptions, that could make a big difference as well. People are much more likely to drive out further if they are more certain they're actually able to get an animal, or if they know they won't need to drive back 1 or 2 more times after they first meet the animal. The same goes for the number of people who are going to be willing to fill out a 1 page application in the first place vs. a multi-page application that asks personal questions.
Also getting your animals on PetFinder and any other pet listing website helps get you exposure when people are doing general searches in the area.
Beyond that, you can try looking at more innovative things like having webcameras on your animals, or going over the top in terms of presentation for bios, descriptions, photos, videos, anything to make your animals more accessible without actually being there.
------------------------------
Jeff Okazaki
Humane Society of Jefferson County
------------------------------