Not enough information in the OP to really respond to. Where are these roads? There's a fair few places where there isn't a parallel route that's not far displaced from the original route, or even more impractical to cycle (unless you're looking for "I climbed XXX road!" bragging rights, or the river's low so you can wade across, etc.). And no shoulders and high speeds doesn't tell you anything without traffic levels. Anyone remember the Adventure Cyclist article a few years back when a group of TransAm riders decided to see if they could ride naked for one mile without anyone seeing them? Boring, flat, straight in that instance meant drivers could see the cyclists for a couple miles (and in that instance, they did!).