Grade (slope)
Grade measures steepness as angle, percentage, or ratio.
Grade (also called slope, incline, mainfall, pitch, or rise) is a measure of the steepness of a physical feature, landform, or constructed line. It is expressed as the elevation angle to the horizontal or its tangent, with zero indicating horizontality and larger numbers indicating steeper tilt. Grade is commonly used for human-made surfaces such as roads, railroads, roof pitches, and pedestrian routes, while the term slope is often applied to natural features like hillsides and river banks.
- field
- Engineering, Geography, Transportation
- known_for
- Measuring steepness of roads, railways, and landforms
- common_expressions
- Percentage, per-mille, ratio (1 in n), angle in degrees
- steepest_recorded_street
- Baldwin Street, Dunedin, New Zealand (34.8% grade, 1 in 2.87)
- maximum_us_federal_highway_grade
- Up to 6% generally, with exceptions up to 7% on mountainous roads below 60 mph
Lore & Background
As the slope approaches vertical, the percentage approaches infinity.
Reader's Guide
Grade is a critical concept in transportation and civil engineering, determining the maximum steepness that vehicles, trains, and pedestrians can safely navigate. The steepest roads in the world, such as Baldwin Street in New Zealand (34.8% grade), highlight the extremes of grade design. In the United States, federally funded highways generally allow up to 6% grade in mountainous areas, with exceptions up to 7% on roads with speed limits below 60 mph. Gradeability—the highest grade a vehicle can ascend while maintaining speed—is a key performance metric for automobiles and trains. The notation system varies by region: percentage is common in the U.S. and Europe, per-mille for European railways, and ratios for roads in Australia, the UK, and Hong Kong. Understanding grade is essential for safe and efficient infrastructure design, from urban streets to mountain railways.
Did You Know?
- The steepest street in the world per Guinness World Records is Baldwin Street in Dunedin, New Zealand, with a 34.8% grade (1 in 2.87).
- In the U.S., federally funded highways generally allow up to 6% grade in mountainous areas, with exceptions up to 7% on roads with speed limits below 60 mph.
Frequently Asked Questions
What exactly is 'grade' in physical geography?
Grade is a way of quantifying how steep a surface or landform is, essentially measuring the angle it makes relative to a flat, horizontal plane. A value of zero means perfectly level, while higher values indicate a more dramatic tilt. The concept applies to everything from mountain ridges to paved roadways.
What is the steepest recorded street in the world?
Baldwin Street in Dunedin, New Zealand holds that title, with a maximum grade of 34.8%, which translates to a ratio of roughly 1 in 2.87. It is a short residential lane that has become a well-known tourist curiosity.
How steep can US federal highways get?
The general cap sits at 6% for most federal highway segments, though mountainous routes with speed limits below 60 mph are permitted to reach up to 7%. These exceptions exist to accommodate the rugged terrain of regions like the Rockies or Appalachians.
What's the difference between 'grade' and 'slope'?
In practice, 'grade' is the term engineers and transportation planners prefer for built infrastructure like roads, rail lines, and rooftops, while 'slope' is the word more commonly attached to natural features such as hillsides and riverbanks. Both describe the same underlying concept of steepness, just applied to different contexts.
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