# Curves

### From LdsigWiki

## North America

Prototype railroads in North America measure curves by degree of curvature, not radius. The degree of curvature is measured by in the field by the offset of a 100 foot chord.

**For a prototype curve:**

R=Radius of the curve

D=Degree of curvature

R=50/sin(D/2)

So for a 4 degree 30 minute curve:

R= 50/sin(4 deg 30 min/2)

R= 50/sin(2 deg 15 min)

R= 50/.0392

R= 1275 feet

**To convert to HO radius in inches:**

Rho= (R/87)x12

Rho= (1275/87)x12

Rho= (14.655)x12

Rho= 175 inches

Typical mainline curves are in the 2-6 degree range. Sharp curves are those above 10 degrees.

## United Kingdom

In the United Kingdom and most countries that belonged to the former British Empire, prototype curves are commonly measured by radius. In pre-metric times, the radius was often measured in chains.

1 chain = 22 yards = 66 feet.