Do you have an example?

I poked around the map of southern PA with RideWithGPS, and couldn't find a road steeper than 10%, although I'm not convinced of the RWGPS accuracy.

I hit about 17% every day with wicked high gearing. Stand up and pull hard. But it is only for a short stretch, and total length of the hill is only about 1/8 mile. The really steep spot is only 50 feet or so. The biggest problem is traction when wet.

I do find that I am highly susceptible to weight. So pull a 50 pound trailer and I'm dropping gears quickly. Pull a few hundred pound trailer, and I can neither pull it up the hill with the bike nor walking (trying to fix that).

I suppose I should hunt for a bit longer 20 to 25% hill