In the 1910s and 1920s, before the creation of the US highway system, an unofficial network of roads called Auto Trails crisscrossed the nation. The Lincoln Highway is perhaps the best known of them. Other well-known trails include the Dixie Highway, the Yellowstone Trail, the National Old Trails Road, the Jefferson Highway, and the Old Spanish Trail. These were major trails that spanned coasts or connected the far north to the deep south. Many smaller trails, some entirely within certain states, also existed.
Auto trails were mostly cobbled together out of existing roads, except out West, where roads sometimes had to be built for these trails. Each trail was managed by an Association, such as the Lincoln Highway Association, which determined it route and promoted it. Each Auto Trail had its mission, such as the Lincoln Highway’s to provide a well-marked transcontinental route. But how any city or town made it onto an auto trail was often a matter of politics and favors. Cities and towns very much wanted to be on these auto trails for the traffic, and therefore commerce, they would bring.
One lesser known — I’d argue little known — transcontinental auto trail was the Pikes Peak Ocean-to-Ocean Highway (PP-OO). It was formed in 1914 to connect New York City to San Francisco through Pennsylvania, the District of Columbia, Maryland, West Virginia, Ohio, Indiana, Illinois, Missouri, Kansas, Colorado, Utah, Nevada, and California.
For reasons lost to time, the road frequently avoided major cities, which hurt its commercial viability and may be why it’s not better known today. Also, I know of no other Auto Trail that changed its route as often as the PP-OO. For a time, it even had two western ends: San Francisco and Los Angeles!
In Indiana, it appears that at first the PP-OO followed the National Road to Indianapolis and then the Rockville State Road to Rockville in western Indiana, and thence to Illinois. This road would become US 36 in 1926.
But in the years that followed, this Auto Trail was heavily realigned. In the end, the PP-OO entered Indiana at Union City and then followed roughly what is now State Road 32 through Winchester, Muncie, and Anderson. Then it connected to what is now US 136 and ran through Crawfordsville and Covington on its way to Danville, Illinois. This new leg in western Indiana was also the Dixie Highway. I explored this section of US 136 in 2012; see those posts here.
Anyone trying to follow the PP-OO at any time really needed an up-to-date trail map!
In 2007 I grew curious about US 36 in western Indiana. It was one of the original US highways in 1926, and in those days its eastern end was in Indianapolis. Tracing US 36 on the map I found a number of possible old alignments, and I wanted to explore them all. This is also when I learned about the PP-OO and its original western-Indiana alignment along the US 36 corridor. I explored US 36 and the PP-OO on two separate trips, May 28 and August 17, 2007. I wrote about it then on my old Roads site, which I’m deprecating. In the weeks to come, I’ll share those stories and photographs here.

Further reading about the PP-OO:
- This site all about the PP-OO
- This page at the Federal Highway Administration
- This set of 1915-16 maps at the Federal Highway Administration
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