U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
Diagram of an east/west roadway with a curve that causes it to be come a north-northwest/south-southeast roadway.
The roadway shows two images of a vehicle in the right lane traveling north/northwest. A grey arrow that curves with the roadway indicates the trajectory of the vehicle's path. The arrow initially is centered within the travel lane, but as the vehicle begins to turn left to navigate the curve, the center line of the vehicle shifts to the left side of the lane at the sharpest point in the curve before returning to its centered position within the travel lane. The point where the grey arrow line is closest to the edge of the lane is labeled as the Curve Radius, R. The point where the grey line completes the curve and returns to a centered position within the lane is labeled Path Radius, Rp.
Along the outer edge of the curve (to the right of the roadway in the diagram) a straight, diagonal line extends upward and slightly to the left. this line begins at the point where the road begins to curve, indicating the path the roadway would take if it did not curve, but rather went straight. A second line extends horizontally from left to right, back from the point at which the road straigthens out, to intersect the diagonal line. The angle at which the two meet is labeled the Deflection Angle, lc.