Banradien

Banradien, or the track radius, is the radius of curvature of a horizontal alignment in railway and road design. It is defined as the radius of the circular arc that approximates a curved section of a track or roadway. In practice, alignments often combine straight segments with curved ones; the core curved segment uses a constant radius, though transition curves may be used to provide a gradual change in curvature.

The banradien is a key parameter for vehicle dynamics, safety, and comfort. A smaller radius creates a sharper bend, increasing lateral acceleration and the potential for wheel-rail or tire wear and loss of stability. A larger radius produces a gentler curve suitable for higher speeds and smoother travel. The radius interacts with cant (superelevation) to balance centrifugal forces, particularly on rails, where proper cant helps maintain wheel-rail contact and stability through curves.

In railway engineering, the banradien is chosen to satisfy speed targets, axle loads, track durability, and clearance constraints. In road design, it depends on design speed, expected vehicle types, driver comfort, and surrounding constraints. Standards and guidelines prescribe minimum or recommended radii for different classes of roads and lines; high-speed lines and major roads typically employ larger radii, while urban or industrial routes may use smaller radii with appropriate transition curves and cant.

Related concepts include radius of curvature, cant, and horizontal alignment design. Transition curves, such as clothoids, are often used to connect straight sections to circular arcs to ensure a smooth change in curvature.