A 20% incline is considered extremely steep and is significantly steeper than almost any standard public road. In engineering terms, a 20% grade means that for every 100 feet of horizontal distance, the elevation rises by 20 feet. To put this in perspective, most interstate highways in the United States are limited to a maximum grade of 6% or 7%. A 20% incline is roughly equal to an angle of 11.3 degrees. For a pedestrian, walking up a 20% slope feels like a strenuous hike and will quickly increase your heart rate; for a cyclist, it is a "category-killing" climb that requires significant power and low gearing. Most standard front-wheel-drive cars may struggle with traction on a 20% incline if the road is wet or icy. In the world of treadmills, a 20% setting is usually the maximum limit for high-end "incline trainers" and is used for intense calorie burning. If you encounter a 20% grade on a residential street—which is rare but does happen in cities like San Francisco or Pittsburgh—it is often steep enough that the sidewalk may be replaced with stairs to assist pedestrians in navigating the vertical rise safely.