Trying to quantify difference between two overlapping lines.

[MitchellCarey]

I'm trying to find a way to quantify the difference between two lines. Here's the situation; We have a GPS Track of a proposed road and Design line for that road from the contractor, and we want to find how far, on average, the GPS Track is from the design line. I've attached a picture here. The yellow line is the design line and the black one is the GPS track. The red buffer is a line buffer at 1-foot increments, and it's part of a method I used to find this answer but I'm just wondering if there's a more statistically sound way to answer this question. 

[EdwardGause]

You could write a routine that grab the vertices from one line, found the closest vertices in the other line, get the distance between those 2 vertices. Now you just need to sum all of the distances you grab from doing that operation above for each vertices, and divide by the number of vertices to get average distance between the lines.  I would suggest doing this in python with the ESRI API's for python, but I believe it would also be possible in Model Builder.