One thing I find helps is a good map with a good legend. I rarely worry about a US highway. Many state highways are good, some not. In some states, like Indiana, many county highways are also good, but not all. The key, for me, to figuring out which are "likely" to be good and which are less so, is the legend on that map.
In the legend, note that the better roads seem to have wider and/or bolder lines to depict the highway. While this approach is not an end-all solution, it sure helps me in choosing which highways to take, especially since we prefer the non-interstates as far more interesting travel.
We've only very rarely had to change a route because of low clearance. For determining where those are, I use the Motor Carriers Atlas that Robbie spoke of, available at many fine bookstores and truckstops. In the front it lists all the low clearance locations as provided by the state governments. I believe it is for federal and state highways and may or may not include county roads, depending on the state.
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