This Is (Probably) The Steepest Stretch Of Highway In The US

Say what you will about its politics, but the United States of America has one of the most interesting topographical profiles on the planet. Pair that with our borderline addiction to automobiles, and you get some seriously steep roadways, having to navigate some genuinely gnarly peaks and valleys.

There isn't a Guinness World Records entry for "America's steepest stretch of highway," nor has the official Road Steepness Rankings Society (a totally real organization I didn't just make up) issued a press release declaring any winners. However, most sources say Sonora Pass, a.k.a. Highway 108 in California's Sierra Nevada Range, has some of the steepest, if not the steepest, stretches of highway in the country.

Located about 90 minutes from Sacramento, stretching 80 miles long and reaching 9,624 feet above sea level at its summit, making it apparently the second-highest paved pass in the state. The steepest sections of Sonora Pass apparently hit a maximum grade of 26%, said to occur as you approach the summit.

For reference, grade is measured as the rise divided by the run, meaning a theoretical 100% grade is equivalent to 45 degrees. Therefore, 26% here is equal to a road with an incline of about 14.6 degrees. For comparison, the steepest streets in the famously hilly city of San Francisco exceed 30%, and one even logs 41%, but those are city streets, not highways. Los Angeles, meanwhile, has streets that are steep enough to launch Teslas into the air, with Eldred St peaking at 33.3%. 

Still, a 26% grade is absolutely nothing to sneeze at, and among motorcyclists, Sonora is a particular challenge not recommended for novices or first-time riders. Not only is it steep, but the switchbacks are tight, corners are blind, there aren't that many guardrails, and the air is thin from sheer altitude. Caltrans, in fact, closes it from about November to April when there's snow, and there are apparently very few fuel stops along the way. Perhaps not treacherous enough to rank on a list of most dangerous roads in the world, but still not one to take lightly if the goal is to ride a motorcycle or drive a performance car through there quickly. 

At any rate, here's a video of a guy who took his Ford Model A up Sonora Pass. You can watch as it struggles to get up the 25% grade at around 5 minutes in.