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 detailed turn-by-turn directions that put Google to shame, pointing out landmarks like cemeteries, factories, and places where the road crossed trolley tracks.

The Blue Book guides and others like them were the predecessors to road maps and atlases, says John Bauer, a geographer at the University of Nebraska at Kearney, who published what may be the only academic study of the series. Bauer suspects the guides may have even influenced some of the routes chosen for the state and federal highway networks built in the subsequent decades.

View Images The leather cover and gilt lettering were designed to give the Blue Book guides an authoritative look. Prelinger Library / Photo by Greg Miller

I recently spent some time flipping through a 1916 volume at the Prelinger Library in San Francisco. It covered a huge swath of the country, from the Mississippi River to the Pacific Coast. With a leather cover and gilt lettering, the guide had the look and heft of a Bible. It included 1,286 individual routes—actually more, because some routes had lettered side routes. Route 528, for example, takes you from Fort Morgan, Colorado to Denver, via Greely, while route 528A takes you from Greely up to Estes Park.

What struck me, in addition to the sheer number of routes and their complexity (the 115-mile route from Fort Morgan to Denver had 40 steps), was the volume’s boosterish tone. The ads, with photos of well-dressed, apparently well-heeled people, make driving look très sophisticated. If cars had cupholders back then, these folks would be rolling with crystal goblets, not Big Gulps.

A section on Transcontinental Touring extolls the “wonders of the western country,” and urges readers not to be daunted by the journey, reminding them that at least 5,000 cars had made the trip from the Mississippi to the Pacific in the last two years. Five whole thousand! “True, the unexpected happens in those less developed and more sparsely settled sections of the country—but those unforeseen occurrences, seldom dangerous or serious, are the very thing that give romance and variety to a Western trip.”

View Images Ads like this one in the 1916 Blue Book reflected the aspirations of the middle class, for whom automobile ownership had only recently come within reach. Prelinger Library / Photo by Greg Miller

The Blue Book guides (which aren’t related to the Kelly Blue Book guides to car values still published today) were intended to look authoritative and to drum up enthusiasm for automobile touring, Bauer writes in his paper, published in Cartographic Perspectives in 2009. The guides also met a pressing need for navigational aids at the time. “They were uniquely suited for navigating the primitive network of local roads that existed prior to the 1920s,” he writes.

In the early 20th century, a trip from, say, Chicago to Denver, would involve hundreds of turns on small local roads that wound their way through the countryside and zig-zagged through towns. Road signs were virtually nonexistent, Bauer says, because until cars came along there was no need for them. Long trips were made by train, and virtually all short trips were made by local people who already had a mental map of the roads in their area.

Cars changed everything. By 1916, they were well on their way to becoming more than just a toy for the wealthy (all the same, those fancy people in the Blue Book ads reflected the aspirations of the newly automobiled middle class). The number of cars registered in the U.S. had doubled in the last two years, reaching 3.4 million (compared to 188 million in 2014). Lots more people were driving. And lots of them were getting lost.

The instructions for using the Blue Book guides (see below) seem complicated now, but they made sense in the context of the times. “You don’t drive but one or two or three miles before you have to turn,” Bauer told me. “It’s impossible to show all those turns at the scale of a typical map.”

View Images This diagram explains how to use the reference maps to look up detailed driving directions between two places. Prelinger Library / Photo by Greg Miller

The guides do contain maps, but most of them aren’t meant to be used directly in navigation. Rather, they serve as a visual index to the written turn-by-turn directions. Like railroad maps, these index maps depict straight-line connections between towns, even when the actual routes were far more convoluted.

And convoluted they were. Here are two steps in the directions from Fort Morgan to Denver:

3.4 1.7 End of road, turn right; curving left just beyond. Pass school on left 4.4. Turn right with road 5.0. Cross concrete bridge 5.2. 8.8 5.4 End of road; turn right with travel. Cross bridge over Platte River and RR. 9.2

The numbers refer to mileage. The first number for each step is the total distance traveled so far, the second is the intermediate distance you’d see on your odometer if you re-zeroed it at the beginning of each step. For example, at the start of the second step above, you’d be 8.8 miles into the entire trip, and you’d have just finished the 5.4 mile segment described in the previous step (you’d have passed the school at 4.4 miles, the concrete bridge at 5.2, and hit 5.4 at the end of the road, right where the second step begins). Easy, right?

Well, following all these twists and turns would have been easier back when cars rarely broke 30 miles per hour, Bauer says, and there was time for a driver (or better whoever was riding shotgun) to look back and forth between the book and the road ahead.

View Images This section of the 1916 guide shows driving directions between Greely and Estes Park, Colorado. Prelinger Library / Photo by Greg Miller

Even so, following these directions would require two things: a good odometer and a degree of diligence. If you got off track all your numbers would be off. You’d have to find your way back to the nearest point of reference.

The Blue Book guides weren’t purely for navigation. They also include introductions to towns and cities and flag points of historical or modern interest. The Fort Morgan-Denver route description, for example, includes this gem: “The intrepid Hollen Godfrey maintained a stage station at a point located near Merino. He was often attacked by Indians, but was never caught napping…”

Not much is known about how the Blue Book guides were made, Bauer says, but the publisher apparently paid professional “pathfinders” to drive the main roads each summer so the guides could be updated to reflect the quickly-changing road conditions. Amateur pathfinders, often members of local automotive clubs, also contributed.

View Images This index map shows the main roads leading in and out of Chicago. Prelinger Library / Photo by Greg Miller

In a way, the success of the guides may have contributed to their demise. As more people felt emboldened to hit the road, pressure mounted on the government to build better roads. The Federal Aid Road Act of 1916 provided the first federal funding for building and improving roads. In 1926, the first network of numbered interstate highways was established. As signs went up along these routes, it became far easier to navigate without turn-by-turn directions.

Two years earlier, in 1924, Rand McNally had published its “Auto Chum,” the first edition of what would become its bestselling road atlas. Other companies soon jumped on the road-atlas band wagon. After 1927, the Blue Book guides with turn-by-turn directions were no longer published.

It’s ironic that nearly a century later, after decades of relying on road maps and atlases, so many drivers have gone back to turn-by-turn directions as their preferred navigational aid. If only Siri could flag the landmarks and throw out some trivia along the way.