A cross-country road trip is a quintessentially American experience. From Jack Kerouac to the Griswold family, millions have loaded up the car and hit the open road. It’s always an adventure, but in modern times it’s a relatively tame one: The roads are paved, signs point the way, and Siri always has your back.

But a hundred years ago, traveling cross-country by automobile was intimidating, if not a little bit dangerous. Cars were unreliable. Roads were rough, and with the Interstate Highway System still decades away, a bewildering array of potential routes connected any pair of distant points.

A crucial aid in those days was a series of guides called the Official Automobile Blue Book. Each thick volume covered hundreds of routes, giving