A: Route 66 had many alignments since it was commissioned in 1926. As time passed, its roadbed was improved and by 1938 the full length of the highway had been paved.
However, later, as the Interstate system replaced sections of the original Route 66, some of these segments were not maintained and fell in disrepair.
Although most of the road is paved, there are some segments that are unpaved: Glenrio to San Jon in New Mexico is a gravel surfaced road. The Jericho Gap in TX is still a dirt road. These can be bypassed along I-40.
Other sections of the road were integrated as the frontage roads of the Interstate highways, so they are well up kept. Other sections may be temporarily closed due to damage (as was the case in California after severe flood damage in the Mojave in late 2014 which are still closed!).
And other parts of US 66 are now overlaid by the freeway, buried beneath the newer alignment.
>> Learn more about Road Conditions along U.S. 66.