The interactive map (link above) shows which streets have been overlayed* in the City of Littleton since 1981. The default view is 1981-1982. To view more years at once, slide the rightmost blue marker in the time slider under the map to increase the number of years shown. Click the "Play" button just above the slider to animate the map forward in time.
*Asphalt overlay is a paving method where a new layer of hot asphalt is applied to a prepared street. To prepare for an overlay, the street is usually milled first, which involves grinding off 1 to 3 inches of the existing asphalt, filling potholes and repairing cracks.