detect ramp center-line from image

Hi, i have an aerial image captured for some road ramp,I want to automatically detect the ramp center-line which assumed to be located in the middle of the road lane,considering the widening factors that exists in some places, after determining the center-line, I want to divide it every 1 meter and extract the curvature at each point.. please find the attached example of the aerial image.. if you could do it please contact me..i will send you the original image