Positioning an object on a curve with out using X, Y

Hi! All
I have a route (curve on the stage) and a point (round shape which acts as a vechile). I pass the x,y axis values for distance to the point so that the point lies exactly on the line. Starting point of curve is 0 miles and the end is 100 miles. so if i want to place the point (vechile) at 10 miles then i have to maually find x,y axis values and the pass them on to the point using xml file. but instead of passing X, y values i want to covet it to numbers so the each number is equalant to mile. if i pass 1, then the point should appear on the curve at 1 mile distance.

Please hlep me on this.

Thank you
krishnam