Just go out and push the pedals 
because the next drop ride nobody is going to be waiting. I ride enough in the mountains to know it isn’t possible for everyone, like some friends that have 10% grades out the front door. Personally I find 2 hours on the trainer to border on the impossible, and freely admit that is a mental barrier and will do whats necessary to get faster. Just 6 weeks ago I did 3 hours on the trainer because of bad air quality - longest trainer ride ever with 15 minutes of ‘coasting’ in order to survive!
Whats an American Highway? I leave town and see/smell a lot of cows and hawks and vineyards and distant views of HC climbs.