I have lines along sidewalks those lines have gaps between them. I want to bridge the gaps with a 5' threshold. Extend doesn't seem to work with lines pointing the same direction, and only perpendicular(mostly) cases. Here's a photo of my situation where the white line is my sidewalk layer, and the black line is my working layer that I want to fill the gaps of: 
Tools like snap, integrate, and ET Geowizard's Clean Polygons don't quite work because some segments are smaller the gaps between them, so the snapping threshold envelops those smaller segments. The only thing that seems to work is using the snap tool in conjunction with the merge and explode edit tools - snapping with 1' threshold, merging all then exploding all, then snapping with a 2' threshold, and so forth till i get to 5'.
Additionally, I've tried making this in Model Builder with Snap and Unsplit Lines tools but can't quite figure out the configuration to iterate thresholds.
